Topics

Type 503 Oscilloscope Issues

Evan
 

I am hoping some members may be able to help with my current problem.



I have been having issues with a Type 503 that I recently acquired from an old electronics/mechanical engineering lab at school (has not been used since the 1970s). The scope had been working for the past week, but then started losing quality in XY mode, with the (-) Input horizontal channel becoming weaker. Yesterday I had run the scope for about 2 hours, and then all signals cut out, with a smell of something burning. The beam is no longer able to center itself, being blurred and flickering sporadically. The scope also makes a loud buzzing sound, which seems to be coming from one of the voltage regulator tubes (based on flickering and visibly seeing the blue electron beam on the 6DQ6A tube wall). However, I am not sure if this is due to a bad tube itself, or a bad capacitor (as I have read that these are prone to failure).


From old Tektronix manuals and support articles on the 503 model, I have confirmed that the model I have has the re-grounding fix for the defect that earlier models were shipped with, and that none of the capacitors have paper caps (all plastic).


Below are links to videos I took of the oscilloscope while running to help visualize the issue.


1. https://www.youtube.com/watch?v=E0-eOiXtlLg
2. https://www.youtube.com/watch?v=bMev4rrkUdw
3. https://youtu.be/A0uav9mEhEI
4. https://youtu.be/C2TuEq5nd40


Any help with this is much appreciated, since I am not familiar with analog tube scopes, and the electronics inside it are beyond anything my electrical engineering friends can figure out.




- Evan

Dave Casey
 

Step 1: Get better friends.
Step 2: Read the manual. There's a whole section on troubleshooting the
scope, including the power supply which is where your problems appear to
be.

You should be able to narrow things down by taking a few DC voltage
measurements. BE CERTAIN to use a quality meter and leads for those
measurements, as the voltages present in old tube gear are not to be
handled casually. For example, in the power supply troubleshoot section it
tells you to look for a voltage of around 500V at one location, and 600 or
more at another. These voltages are derived from AC, so they're going to
have ripple on them, especially if the equipment is malfunctioning. Don't
use a meter that isn't rated to at least 600 VAC or you're taking some
risks. If it all possible, clip the probes on before plugging in and
powering on the scope; touch nothing while you record your measurement, and
then turn it off and unplug it before moving on to the next measurement.
That said, the light show going on in the power supply is not normal. V659
(the regulator tube making the fuss in your video) is the vacuum tube
analog of a zener diode with a Vz of 85V. The current through this tube is
limited by R659. You should have a good look at R659 and measure it with
the scope off and unplugged (and give the caps some time to discharge). You
shouldn't notice a difference in measurement whether or not V659 is
installed. It's very possible that your only problem is V659 and, as a
result, a burned R659. Tubes don't make burning smells, so use a bright
light to look for any obvious damage on the Rs, Ls, and Cs (scope doesn't
need to be on for this). You can also measure the DC voltage at pins 1 and
5 of V659 and see if it's regulating properly (should be about 85V, but
could be upwards of 250V if V659 is failing). The blue glow in the 6DQ6
(V620) is extra electrons hitting the glass; this may or may not be
indicative of a problem, but I'd pay closer attention to V659 first; V659
has some feedback to V620 through V634. I would also verify that D652 is
still a diode.

Good luck! Let us know what you find, but be safe!

Dave Casey

On Sat, Apr 1, 2017 at 7:34 PM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



I am hoping some members may be able to help with my current problem.



I have been having issues with a Type 503 that I recently acquired from an
old electronics/mechanical engineering lab at school (has not been used
since the 1970s). The scope had been working for the past week, but then
started losing quality in XY mode, with the (-) Input horizontal channel
becoming weaker. Yesterday I had run the scope for about 2 hours, and then
all signals cut out, with a smell of something burning. The beam is no
longer able to center itself, being blurred and flickering sporadically.
The scope also makes a loud buzzing sound, which seems to be coming from
one of the voltage regulator tubes (based on flickering and visibly seeing
the blue electron beam on the 6DQ6A tube wall). However, I am not sure if
this is due to a bad tube itself, or a bad capacitor (as I have read that
these are prone to failure).


From old Tektronix manuals and support articles on the 503 model, I have
confirmed that the model I have has the re-grounding fix for the defect
that earlier models were shipped with, and that none of the capacitors have
paper caps (all plastic).


Below are links to videos I took of the oscilloscope while running to help
visualize the issue.


1. https://www.youtube.com/watch?v=E0-eOiXtlLg
2. https://www.youtube.com/watch?v=bMev4rrkUdw
3. https://youtu.be/A0uav9mEhEI
4. https://youtu.be/C2TuEq5nd40


Any help with this is much appreciated, since I am not familiar with
analog tube scopes, and the electronics inside it are beyond anything my
electrical engineering friends can figure out.




- Evan



[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]

 

Evan:

In addition to the advice offered by Dave Casey, let me add the following:

I looked at the youtube videos that you posted. Perhaps others will be able to draw conclusions from the videos, but I wasn't able to do so. I also tried to listen to the background sound(s), but I couldn't hear anything that gave any clues. The buzzing sound that you mention in your original post might be coming from one of the power transformers (T601, or T620), rather than a tube per se. I do suspect that the buzzing sound is indicative/symptomatic of a genuine problem.

Do you have the tools to measure the DC bus voltages within the 503? If you have a suitable voltmeter(s), and if you are confident that you can make these measurements _safely_, then this is the first step. Personally, I prefer analog voltmeter(s) for this type of measurement, if available. Hopefully all of the DC bus voltages (+500, +250, +85, +100, -100, +12.6, -3000) are within spec limits and are rock-steady. If the DC voltages check out, an AC voltmeter can be used to verify that the ripple is also within spec (except for the -3000V bus). The spec limits for the DC voltages, and the allowable ripple on each DC bus, are indicated in the 503 manual (available from the BAMA boat anchor site; probably also at WWW.W140.com). The manual also shows locations for accessing the different bus points for measurement.

Be careful when making these measurements, as these older vacuum tube scopes have voltages and energy levels that can kill. If you aren't comfortable or confident working with these voltages, find someone to help you out.

I suspect that your scope has (at least) some issues with the power supplies. I have a RM504 scope (similar power supply to the 503 series) and I had to repair some power supply problems associated with power transformer T601. When I did the repair (several years ago) I researched the Tekscopes user group archives and found that the 503/504 series of scopes had problems with (a) T601 short-to-ground of the CRT filament winding, (b) T620 short(s)-to-ground or turn-to-turn shorts, usually of the 3000V winding, (c) silicon rectifier diode failures, and (d) electrolytic capacitor failures. Item (a) was the issue with my RM504. Unfortunately, the listserver is a lot more "clunky" to do searches on these days, since Yahoo groups made "improvements." However, there are many Tek owners on this listserver with 503 or similar-generation scopes who can offer advice.

Good luck and keep us informed. The 503 is a nice scope- wish I had one!

Mike Dinolfo N4MWP

Leon Robinson
 

I have a 502 that had the same CRT filament winding short that Mike described.
I had to add a 6.3 volt filament transformer with high voltage insulation in
place of the shorted winding in the big power transformer.
There was enough room under the main chassis and I oriented the transformer to
minimize the magnetic field effects on the CRT.
Good luck. Leon Robinson    K5JLR

Political Correctness is a Political Disease.

From: "Mike @mdinolfo [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Saturday, April 1, 2017 8:50 PM
Subject: Re: [TekScopes] Type 503 Oscilloscope Issues

Evan:

In addition to the advice offered by Dave Casey, let me add the following:

I looked at the youtube videos that you posted.  Perhaps others will be
able to draw conclusions from the videos, but I wasn't able to do so.  I
also tried to listen to the background sound(s), but I couldn't hear
anything that gave any clues.  The buzzing sound that you mention in
your original post might be coming from one of the power transformers
(T601, or T620), rather than a tube per se.  I do suspect that the
buzzing sound is indicative/symptomatic of a genuine problem.

Do you have the tools to measure the DC bus voltages within the 503?  If
you have a suitable voltmeter(s), and if you are confident that you can
make these measurements _safely_, then this is the first step.
Personally, I prefer analog voltmeter(s) for this type of measurement,
if available.  Hopefully all of the DC bus voltages (+500, +250, +85,
+100, -100, +12.6, -3000) are within spec limits and are rock-steady.
If the DC voltages check out, an AC voltmeter can be used to verify that
the ripple is also within spec (except for the -3000V bus).  The spec
limits for the DC voltages, and the allowable ripple on each DC bus, are
indicated in the 503 manual (available from the BAMA boat anchor site;
probably also at WWW.W140.com).  The manual also shows locations for
accessing the different bus points for measurement.

Be careful when making these measurements, as these older vacuum tube
scopes have voltages and energy levels that can kill.  If you aren't
comfortable or confident working with these voltages, find someone to
help you out.

I suspect that your scope has (at least) some issues with the power
supplies.  I have a RM504 scope (similar power supply to the 503 series)
and I had to repair some power supply problems associated with power
transformer T601.  When I did the repair (several years ago) I
researched the Tekscopes user group archives and found that the 503/504
series of scopes had problems with (a) T601 short-to-ground of the CRT
filament winding, (b) T620 short(s)-to-ground or turn-to-turn shorts,
usually of the 3000V winding, (c) silicon rectifier diode failures, and
(d) electrolytic capacitor failures.  Item (a) was the issue with my
RM504.  Unfortunately, the listserver is a lot more "clunky" to do
searches on these days, since Yahoo groups made "improvements."
However, there are many Tek owners on this listserver with 503 or
similar-generation scopes who can offer advice.

Good luck and keep us informed.  The 503 is a nice scope- wish I had one!

Mike Dinolfo N4MWP




------------------------------------

------------------------------------


------------------------------------

Yahoo Groups Links







[Non-text portions of this message have been removed]

Daniel Koller
 

HI Evan,
  Good luck.  Yes, there are a number of us here with working RM503s/504s.    Mike D summed up the common problems of this scope pretty well.   I might add that failure of T620 is more or less fatal (to the scope) as T620 is "unobtanium" and so the only way to get another one is to take apart another working scope.   
  However, you say you have a beam so that seems unlikely.   Failure in T601 is more likely, and as has been mentioned, it's repairable.  You might explore very carefully with your nose (and the scope off!) and try to narrow down the source of the smell.  Or look for smoke trails.  Then also very carefully listen for the arcing you describe.   Literally find the smoking gun....
   If you can't find it that way, you'll have to track down voltages and resistances to try to deduce the problem, but it's really helpful if you can catch the failure as it's happening.
  Dan

On Saturday, April 1, 2017, 4:02:36 PM EDT, Leon Robinson leon-robinson@... [TekScopes] <TekScopes@...> wrote: 
I have a 502 that had the same CRT filament winding short that Mike described.
I had to add a 6.3 volt filament transformer with high voltage insulation in
place of the shorted winding in the big power transformer.
There was enough room under the main chassis and I oriented the transformer to
minimize the magnetic field effects on the CRT.
Good luck. Leon Robinson    K5JLR

Political Correctness is a Political Disease.

From: "Mike @mdinolfo [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Saturday, April 1, 2017 8:50 PM
Subject: Re: [TekScopes] Type 503 Oscilloscope Issues

Evan:

In addition to the advice offered by Dave Casey, let me add the following:

I looked at the youtube videos that you posted.  Perhaps others will be
able to draw conclusions from the videos, but I wasn't able to do so.  I
also tried to listen to the background sound(s), but I couldn't hear
anything that gave any clues.  The buzzing sound that you mention in
your original post might be coming from one of the power transformers
(T601, or T620), rather than a tube per se.  I do suspect that the
buzzing sound is indicative/symptomatic of a genuine problem.

Do you have the tools to measure the DC bus voltages within the 503?  If
you have a suitable voltmeter(s), and if you are confident that you can
make these measurements _safely_, then this is the first step.
Personally, I prefer analog voltmeter(s) for this type of measurement,
if available.  Hopefully all of the DC bus voltages (+500, +250, +85,
+100, -100, +12.6, -3000) are within spec limits and are rock-steady.
If the DC voltages check out, an AC voltmeter can be used to verify that
the ripple is also within spec (except for the -3000V bus).  The spec
limits for the DC voltages, and the allowable ripple on each DC bus, are
indicated in the 503 manual (available from the BAMA boat anchor site;
probably also at WWW.W140.com).  The manual also shows locations for
accessing the different bus points for measurement.

Be careful when making these measurements, as these older vacuum tube
scopes have voltages and energy levels that can kill.  If you aren't
comfortable or confident working with these voltages, find someone to
help you out.

I suspect that your scope has (at least) some issues with the power
supplies.  I have a RM504 scope (similar power supply to the 503 series)
and I had to repair some power supply problems associated with power
transformer T601.  When I did the repair (several years ago) I
researched the Tekscopes user group archives and found that the 503/504
series of scopes had problems with (a) T601 short-to-ground of the CRT
filament winding, (b) T620 short(s)-to-ground or turn-to-turn shorts,
usually of the 3000V winding, (c) silicon rectifier diode failures, and
(d) electrolytic capacitor failures.  Item (a) was the issue with my
RM504.  Unfortunately, the listserver is a lot more "clunky" to do
searches on these days, since Yahoo groups made "improvements."
However, there are many Tek owners on this listserver with 503 or
similar-generation scopes who can offer advice.

Good luck and keep us informed.  The 503 is a nice scope- wish I had one!

Mike Dinolfo N4MWP

------------------------------------

------------------------------------

------------------------------------

Yahoo Groups Links




#yiv1508870725 #yiv1508870725 -- #yiv1508870725ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv1508870725 #yiv1508870725ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv1508870725 #yiv1508870725ygrp-mkp #yiv1508870725hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv1508870725 #yiv1508870725ygrp-mkp #yiv1508870725ads {margin-bottom:10px;}#yiv1508870725 #yiv1508870725ygrp-mkp .yiv1508870725ad {padding:0 0;}#yiv1508870725 #yiv1508870725ygrp-mkp .yiv1508870725ad p {margin:0;}#yiv1508870725 #yiv1508870725ygrp-mkp .yiv1508870725ad a {color:#0000ff;text-decoration:none;}#yiv1508870725 #yiv1508870725ygrp-sponsor #yiv1508870725ygrp-lc {font-family:Arial;}#yiv1508870725 #yiv1508870725ygrp-sponsor #yiv1508870725ygrp-lc #yiv1508870725hd {margin:10px 0px;font-weight:700;font-size:78%;line-height:122%;}#yiv1508870725 #yiv1508870725ygrp-sponsor #yiv1508870725ygrp-lc .yiv1508870725ad {margin-bottom:10px;padding:0 0;}#yiv1508870725 #yiv1508870725actions {font-family:Verdana;font-size:11px;padding:10px 0;}#yiv1508870725 #yiv1508870725activity {background-color:#e0ecee;float:left;font-family:Verdana;font-size:10px;padding:10px;}#yiv1508870725 #yiv1508870725activity span {font-weight:700;}#yiv1508870725 #yiv1508870725activity span:first-child {text-transform:uppercase;}#yiv1508870725 #yiv1508870725activity span a {color:#5085b6;text-decoration:none;}#yiv1508870725 #yiv1508870725activity span span {color:#ff7900;}#yiv1508870725 #yiv1508870725activity span .yiv1508870725underline {text-decoration:underline;}#yiv1508870725 .yiv1508870725attach {clear:both;display:table;font-family:Arial;font-size:12px;padding:10px 0;width:400px;}#yiv1508870725 .yiv1508870725attach div a {text-decoration:none;}#yiv1508870725 .yiv1508870725attach img {border:none;padding-right:5px;}#yiv1508870725 .yiv1508870725attach label {display:block;margin-bottom:5px;}#yiv1508870725 .yiv1508870725attach label a {text-decoration:none;}#yiv1508870725 blockquote {margin:0 0 0 4px;}#yiv1508870725 .yiv1508870725bold {font-family:Arial;font-size:13px;font-weight:700;}#yiv1508870725 .yiv1508870725bold a {text-decoration:none;}#yiv1508870725 dd.yiv1508870725last p a {font-family:Verdana;font-weight:700;}#yiv1508870725 dd.yiv1508870725last p span {margin-right:10px;font-family:Verdana;font-weight:700;}#yiv1508870725 dd.yiv1508870725last p span.yiv1508870725yshortcuts {margin-right:0;}#yiv1508870725 div.yiv1508870725attach-table div div a {text-decoration:none;}#yiv1508870725 div.yiv1508870725attach-table {width:400px;}#yiv1508870725 div.yiv1508870725file-title a, #yiv1508870725 div.yiv1508870725file-title a:active, #yiv1508870725 div.yiv1508870725file-title a:hover, #yiv1508870725 div.yiv1508870725file-title a:visited {text-decoration:none;}#yiv1508870725 div.yiv1508870725photo-title a, #yiv1508870725 div.yiv1508870725photo-title a:active, #yiv1508870725 div.yiv1508870725photo-title a:hover, #yiv1508870725 div.yiv1508870725photo-title a:visited {text-decoration:none;}#yiv1508870725 div#yiv1508870725ygrp-mlmsg #yiv1508870725ygrp-msg p a span.yiv1508870725yshortcuts {font-family:Verdana;font-size:10px;font-weight:normal;}#yiv1508870725 .yiv1508870725green {color:#628c2a;}#yiv1508870725 .yiv1508870725MsoNormal {margin:0 0 0 0;}#yiv1508870725 o {font-size:0;}#yiv1508870725 #yiv1508870725photos div {float:left;width:72px;}#yiv1508870725 #yiv1508870725photos div div {border:1px solid #666666;height:62px;overflow:hidden;width:62px;}#yiv1508870725 #yiv1508870725photos div label {color:#666666;font-size:10px;overflow:hidden;text-align:center;white-space:nowrap;width:64px;}#yiv1508870725 #yiv1508870725reco-category {font-size:77%;}#yiv1508870725 #yiv1508870725reco-desc {font-size:77%;}#yiv1508870725 .yiv1508870725replbq {margin:4px;}#yiv1508870725 #yiv1508870725ygrp-actbar div a:first-child {margin-right:2px;padding-right:5px;}#yiv1508870725 #yiv1508870725ygrp-mlmsg {font-size:13px;font-family:Arial, helvetica, clean, sans-serif;}#yiv1508870725 #yiv1508870725ygrp-mlmsg table {font-size:inherit;font:100%;}#yiv1508870725 #yiv1508870725ygrp-mlmsg select, #yiv1508870725 input, #yiv1508870725 textarea {font:99% Arial, Helvetica, clean, sans-serif;}#yiv1508870725 #yiv1508870725ygrp-mlmsg pre, #yiv1508870725 code {font:115% monospace;}#yiv1508870725 #yiv1508870725ygrp-mlmsg * {line-height:1.22em;}#yiv1508870725 #yiv1508870725ygrp-mlmsg #yiv1508870725logo {padding-bottom:10px;}#yiv1508870725 #yiv1508870725ygrp-msg p a {font-family:Verdana;}#yiv1508870725 #yiv1508870725ygrp-msg p#yiv1508870725attach-count span {color:#1E66AE;font-weight:700;}#yiv1508870725 #yiv1508870725ygrp-reco #yiv1508870725reco-head {color:#ff7900;font-weight:700;}#yiv1508870725 #yiv1508870725ygrp-reco {margin-bottom:20px;padding:0px;}#yiv1508870725 #yiv1508870725ygrp-sponsor #yiv1508870725ov li a {font-size:130%;text-decoration:none;}#yiv1508870725 #yiv1508870725ygrp-sponsor #yiv1508870725ov li {font-size:77%;list-style-type:square;padding:6px 0;}#yiv1508870725 #yiv1508870725ygrp-sponsor #yiv1508870725ov ul {margin:0;padding:0 0 0 8px;}#yiv1508870725 #yiv1508870725ygrp-text {font-family:Georgia;}#yiv1508870725 #yiv1508870725ygrp-text p {margin:0 0 1em 0;}#yiv1508870725 #yiv1508870725ygrp-text tt {font-size:120%;}#yiv1508870725 #yiv1508870725ygrp-vital ul li:last-child {border-right:none !important;}#yiv1508870725

[Non-text portions of this message have been removed]

Dave Casey
 

After further review and firing up my own 503 for comparison, here are some
observations:
1. V659 should be emitting a steady glow while it's regulating. Yours is
flickering, but that doesn't necessarily mean the tube is faulty - it could
mean that V659 is not seeing a steady positive DC voltage and is thus going
in and out of regulation cyclically.
2. V692, the leaded (not socketed) tube soldered in at the bottom of the
ceramic strips near where the mains cord comes in, should just have a quiet
orange glow. Yours is going to town and appears to be arcing over within
the tube. This tube is a rectifier tube responsible for generating the -3kV
acceleration voltage for the CRT. That same -3kV is a bias voltage on the
heater of the CRT, and at least one other person on this list has already
commented that the CRT heater winding on T601 was shorted on their scope. I
think it is very likely that you have the same problem.
3. Your V620 (6DQ6) sure looks like it's running hot. I think I can see a
cherry red glow in there aside from the orange glow of the heater just
under the cap. Red is bad. I wouldn't at all be surprised if it was due to
the -3kV leaking back onto the 190Vrms winding at T601.

Once you get this figured out, you should take a close look at all the
silicon diodes to make sure they haven't been overstressed. I feel like
D652 (feeding V659) may already be shorted.

Dave Casey

Evan
 

Thank you everyone for the quick responses and advice.

I had looked over the manual for potential sources early on. The V659 and V692 did stand out to me, as they flickered sporadically when the scope was on (and forgot to mention it in my original posting). My personal RadioShack multimeter only does DC up to 1000 V (and AC at 750 V), but I can get access to others for higher voltages to check the -3000 (and may even have an analog one lying around). I have worked with CRTs in computers before, so I am familiar with procedures for high-voltages and safety.

As for parts, I do have other scopes that things could be taken from, namely a Type 545B, Type 543A, and a Type 564 Storage, but some of these are still used, so it could not be anything permanent, and I am not sure how many of the tubes are compatible. (I am only familiar with the 503 since it was the lightest / most portable one to use.)


For now, I'll let the scope discharge and collect what I can to measure the various components to trace/confirm the issue.


- Evan

Dave Casey
 

Your Radio Shanty meter should be adequate for measuring everything besides
the -3kV, and you can probably learn enough about the cause without
measuring that voltage. Keep in mind that if there is a short in the
transformer, other leads that normally have much smaller potentials on them
may be at -3kV with respect to the scope chassis (and earth ground). It is
always important to consider all the effects of a failure. I would advise
you to not handle your meter while you're taking voltage measurements and
to do your best to isolate the meter from earth ground; use alligator clip
leads to attach the meter to the measurement points while the scope is
unplugged and place the meter on a non-conductive surface. Remember that
you have exposed mains voltage inside the scope case very near where you
intend to measure even when the scope is off. Use a GFCI protected outlet
if at all possible as well.

Obviously, for resistance measurements with the scope unplugged and
discharged, you can just use point probes and go to town.

You can also use your meter to check for hard defects in the tubes of
concern; while much higher voltages are usually used to check tubes for
shorts, you can see a major fault with your DMM. For example, you should
(and likely will, based on your videos) see an open between pins 1 and 2 of
V659.

You will have to unsolder V692 to check it, but you should see only about 6
ohms across the filament (or heater) leads (the two on the same end of the
tube). You should see an open between either of those leads and the plate
lead at the other end of the tube. Here's the datasheet for a little more
detail:
https://frank.pocnet.net/sheets/049/5/5642.pdf
I would not at all be surprised if V692 is now trashed based on that light
show in your video. If you remove yours and compare it to photos of new
tubes online, such as at http://www.radiomuseum.org/tubes/tube_5642.html
you may notice that things have melted. But did T601 cause that, or did
V692 cause it?
If a shorted/arcing T601 is the only thing currently wrong with your scope
(i.e. no collateral damage), then the removal of V692 should restore the
rest of the supplies to their normal voltages. IF YOU DO unsolder anything
from the ceramic strips, it is generally advisable to NOT wick/vacuum all
the old solder out and replace with new. The design of the strips is such
that they work best with silver bearing (~2%) solder, which you typically
won't have on your bench. You may, however, have some in one of your scopes
as Tek often provided small amounts inside the instruments for convenience.
If you get rid of too much of the silver you may lose adhesion to the
ceramic, which is bad for long term reliability of the connection.

You're probably feeling a bit inundated with information and possibilities,
etc. Feel free to report back to the group at each stage of your findings,
and we'll help you narrow things down. It's also very probable that someone
on the list local to you will offer to help you in person if you advertise
your location and ask nicely. I think I can safely say that we are always
happy to see more people learn how to troubleshoot and maintain these
instruments instead of scrapping them for parts.

Dave Casey

On Sun, Apr 2, 2017 at 1:05 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



Thank you everyone for the quick responses and advice.

I had looked over the manual for potential sources early on. The V659 and
V692 did stand out to me, as they flickered sporadically when the scope was
on (and forgot to mention it in my original posting). My personal
RadioShack multimeter only does DC up to 1000 V (and AC at 750 V), but I
can get access to others for higher voltages to check the -3000 (and may
even have an analog one lying around). I have worked with CRTs in computers
before, so I am familiar with procedures for high-voltages and safety.

As for parts, I do have other scopes that things could be taken from,
namely a Type 545B, Type 543A, and a Type 564 Storage, but some of these
are still used, so it could not be anything permanent, and I am not sure
how many of the tubes are compatible. (I am only familiar with the 503
since it was the lightest / most portable one to use.)


For now, I'll let the scope discharge and collect what I can to measure
the various components to trace/confirm the issue.


- Evan






[Non-text portions of this message have been removed]

 

Evan:

Dave Casey has offered some excellent advice. I suggest that you follow Dave's advice and measure the bus voltages (other than the -3000 volt bus), assuming that you feel that you can do so safely.

Once you have measured these voltages and let us know the results, I might be able to suggest an alternate diagnosis approach from what Dave has suggested that would not involve any de-soldering of the ceramic strip connections.

And don't panic (yet) regarding the health of V692; it might survive this whole exercise just fine.

Mike Dinolfo N4MWP

On 04/02/2017 04:38 AM, Dave Casey polara413@... [TekScopes] wrote:


Your Radio Shanty meter should be adequate for measuring everything besides
the -3kV, and you can probably learn enough about the cause without
measuring that voltage. Keep in mind that if there is a short in the
transformer, other leads that normally have much smaller potentials on them
may be at -3kV with respect to the scope chassis (and earth ground). It is
always important to consider all the effects of a failure. I would advise
you to not handle your meter while you're taking voltage measurements and
to do your best to isolate the meter from earth ground; use alligator clip
leads to attach the meter to the measurement points while the scope is
unplugged and place the meter on a non-conductive surface. Remember that
you have exposed mains voltage inside the scope case very near where you
intend to measure even when the scope is off. Use a GFCI protected outlet
if at all possible as well.

Obviously, for resistance measurements with the scope unplugged and
discharged, you can just use point probes and go to town.

You can also use your meter to check for hard defects in the tubes of
concern; while much higher voltages are usually used to check tubes for
shorts, you can see a major fault with your DMM. For example, you should
(and likely will, based on your videos) see an open between pins 1 and 2 of
V659.

You will have to unsolder V692 to check it, but you should see only about 6
ohms across the filament (or heater) leads (the two on the same end of the
tube). You should see an open between either of those leads and the plate
lead at the other end of the tube. Here's the datasheet for a little more
detail:
https://frank.pocnet.net/sheets/049/5/5642.pdf
I would not at all be surprised if V692 is now trashed based on that light
show in your video. If you remove yours and compare it to photos of new
tubes online, such as at http://www.radiomuseum.org/tubes/tube_5642.html
you may notice that things have melted. But did T601 cause that, or did
V692 cause it?
If a shorted/arcing T601 is the only thing currently wrong with your scope
(i.e. no collateral damage), then the removal of V692 should restore the
rest of the supplies to their normal voltages. IF YOU DO unsolder anything
from the ceramic strips, it is generally advisable to NOT wick/vacuum all
the old solder out and replace with new. The design of the strips is such
that they work best with silver bearing (~2%) solder, which you typically
won't have on your bench. You may, however, have some in one of your scopes
as Tek often provided small amounts inside the instruments for convenience.
If you get rid of too much of the silver you may lose adhesion to the
ceramic, which is bad for long term reliability of the connection.

You're probably feeling a bit inundated with information and possibilities,
etc. Feel free to report back to the group at each stage of your findings,
and we'll help you narrow things down. It's also very probable that someone
on the list local to you will offer to help you in person if you advertise
your location and ask nicely. I think I can safely say that we are always
happy to see more people learn how to troubleshoot and maintain these
instruments instead of scrapping them for parts.

Dave Casey

On Sun, Apr 2, 2017 at 1:05 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



Thank you everyone for the quick responses and advice.

I had looked over the manual for potential sources early on. The V659 and
V692 did stand out to me, as they flickered sporadically when the
scope was
on (and forgot to mention it in my original posting). My personal
RadioShack multimeter only does DC up to 1000 V (and AC at 750 V), but I
can get access to others for higher voltages to check the -3000 (and may
even have an analog one lying around). I have worked with CRTs in
computers
before, so I am familiar with procedures for high-voltages and safety.

As for parts, I do have other scopes that things could be taken from,
namely a Type 545B, Type 543A, and a Type 564 Storage, but some of these
are still used, so it could not be anything permanent, and I am not sure
how many of the tubes are compatible. (I am only familiar with the 503
since it was the lightest / most portable one to use.)


For now, I'll let the scope discharge and collect what I can to measure
the various components to trace/confirm the issue.


- Evan





Evan
 

Hello all,

I feel bad that it has been several days since my last posting. Unfortunately, my work is at a standstill right now. Over the past weekend I had focused most of my work on restoring a vintage volt meter (Triplett 630-A), which is now working (and supports up to 6000 V, although I lack the HV leads, so no -3000 V testing yet). As such, I only now have gotten time to focus on the scope.

However, when I connected the leads to the ground (chassis) and -100 V test point, plugged in the scope, and after the brief burning smell, nothing happened (no lights for the scope, no CRT turning on, no tubes activating). I discovered that the fuse had blown during my attempt to get the voltages, but after no luck in going through my fuse stock, I ended up having to order a set of new ones to come in, so that won't be until next week earliest.

For the scope, I was still able to check the non-voltage components on the power circuit. The diodes still check out, with D652 (and others) giving readings of ~0.65-0.65 on my multimeter. However, only diode D672 gave a reading of 0.041 on two different multimeters, so I suspect this one is bad. This one is connected to the +12.6 V circuit.

As for resistors, some also seem to have issues, with R692 (going to V692) being at 1.4-1.5 ohm, but it is supposed to be 4.3 ohm. I admit I am having a bit of difficulty in locating R659, so I was unable to confirm if that one is okay.

Once the fuses come in, I'll let you know how the voltages read out. However, as for the burning, think it may be coming from the wires leading to the T601 (see the photo: https://goo.gl/photos/SvfUM7r7w2VY3zsN8 https://goo.gl/photos/SvfUM7r7w2VY3zsN8)


- Evan

Dave Casey
 

Evan -

1. When you test a diode, you're trying to verify that it only passes
current in one direction, which means you have to test each diode twice.
Diodes can fail open, where they pass no current, or shorted, where they
pass current in both directions. This is often difficult to discern while
the diodes are in circuit, as there are other paths for the test current to
travel. The measurements you have taken don't tell you much since you've
made them in circuit. It is no surprise that the 12.6V diode, D672 measures
differently as there is a very direct loop through the filaments of V334
and V434 to ground and back through T620. Your readings are also ambiguous
without units attached. Are you just putting the meter in diode test mode
and telling us the number it shows? Is that kOhms? We don't know.

2. R692 is going to measure much lower than 4.3 ohms in circuit because
there is a parallel path for the current through T620 and V692 (that
horizontal line on the schematic right below R692).

3. R659 can be located by tracing back from V659 and forward from L654. It
gets trickier thanks to the wiring harness; I'll admit I haven't found mine
yet.

4. The burned wires in your picture are the primary (mains) side of T601.
The more burned of the two is the Line/Hot from the fuse to an extra tab on
T601 where the wiring changes to the shielded wire running to the power
switch. You might check to verify that C614 (the ceramic disc capacitor
hanging off the bottom of T601) has not shorted. You should see a
resistance of about 3 ohms across C614 while in circuit (scope unplugged,
power switch off, fuse or no fuse). If C614 has failed, it is best replaced
with a modern "X" rated, UL listed capacitor of the same value. If it
hasn't, you have other problems either in or beyond T601. (Has anyone here
who's familiar with the elevated filament short seen it cross to the
primary winding?)

You should repair the burnt wiring before attempting to power the scope
again. The wiring to the power switch (the red wire connected to the burned
wire) and the wiring back from the power switch (the smaller white wire
that runs through the harness with the red wire and is connected to T601
3/4) should be checked for damage also. If the fuse keeps blowing, you
should NOT use a higher rated fuse in an attempt to get more time to test
things - you will only cause more damage. The power switch wiring might be
best tested by using a megger since it is shielded along its path through
the scope.

Have any of your attempts to power the scope been through a AFCI or GFCI
outlet? Did the protection ever trip?

Please be careful and talk through your next steps with us before you do
any more powered testing (you can safely measure the resistance across C614
anytime you like as long as the scope is unplugged). You might also tell us
what resistance you measure between the -3000V supply and the chassis (T601
terminal 5 is a good spot), which should be safe to measure so long as the
scope has been off for awhile (it *should* be safe within a second or two);
resistance should be a few megohms, possibly above the range of your meter
in which case the exact value is not critical. The value is determined by
the resistors along the left hand side of the CRT schematic (R840, 841,
842, 844, 845, 847, 849, 851, 852). If the measurement is lower than a few
megohms, then that filament winding in T601 that we've been worrying about
might be to blame. This is another place where a megger might tell you
something useful.

Don't be too proud to ask questions about anything I've said that you don't
understand; if I'm wrong about anything, the other list members will be
quick to call me on it. We don't want you to learn any of this the hard
way, because you may not survive the lesson.

Dave Casey

On Thu, Apr 6, 2017 at 12:02 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



Hello all,

I feel bad that it has been several days since my last posting.
Unfortunately, my work is at a standstill right now. Over the past weekend
I had focused most of my work on restoring a vintage volt meter (Triplett
630-A), which is now working (and supports up to 6000 V, although I lack
the HV leads, so no -3000 V testing yet). As such, I only now have gotten
time to focus on the scope.

However, when I connected the leads to the ground (chassis) and -100 V
test point, plugged in the scope, and after the brief burning smell,
nothing happened (no lights for the scope, no CRT turning on, no tubes
activating). I discovered that the fuse had blown during my attempt to get
the voltages, but after no luck in going through my fuse stock, I ended up
having to order a set of new ones to come in, so that won't be until next
week earliest.

For the scope, I was still able to check the non-voltage components on the
power circuit. The diodes still check out, with D652 (and others) giving
readings of ~0.65-0.65 on my multimeter. However, only diode D672 gave a
reading of 0.041 on two different multimeters, so I suspect this one is
bad. This one is connected to the +12.6 V circuit.

As for resistors, some also seem to have issues, with R692 (going to V692)
being at 1.4-1.5 ohm, but it is supposed to be 4.3 ohm. I admit I am having
a bit of difficulty in locating R659, so I was unable to confirm if that
one is okay.

Once the fuses come in, I'll let you know how the voltages read out.
However, as for the burning, think it may be coming from the wires leading
to the T601 (see the photo: https://goo.gl/photos/SvfUM7r7w2VY3zsN8
https://goo.gl/photos/SvfUM7r7w2VY3zsN8)


- Evan

[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]

Dave Casey
 

One last thing - you might go ahead and verify that the black stuff on the
yellow wire is actually stuff that used to be yellow and has burned as
opposed to something else that has landed on that wire (does is scrape off
and reveal undamaged yellow insulation below?). This black stuff was
present in the video you posted the other day. It may have been there the
whole time you've had the scope and have nothing to do with the burning
smell.

I'm also wondering if the problems I thought I saw with V620 and V659 are
misinterpretations of the video. The red color inside V620 may just be a
reflection of the trace rotation knob, and the "flickering" of V659 now
looks more like a result of the changing camera angle. (V692 definitely
shouldn't be doing what it's doing though!)

DC

On Thu, Apr 6, 2017 at 12:02 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



Hello all,

I feel bad that it has been several days since my last posting.
Unfortunately, my work is at a standstill right now. Over the past weekend
I had focused most of my work on restoring a vintage volt meter (Triplett
630-A), which is now working (and supports up to 6000 V, although I lack
the HV leads, so no -3000 V testing yet). As such, I only now have gotten
time to focus on the scope.

However, when I connected the leads to the ground (chassis) and -100 V
test point, plugged in the scope, and after the brief burning smell,
nothing happened (no lights for the scope, no CRT turning on, no tubes
activating). I discovered that the fuse had blown during my attempt to get
the voltages, but after no luck in going through my fuse stock, I ended up
having to order a set of new ones to come in, so that won't be until next
week earliest.

For the scope, I was still able to check the non-voltage components on the
power circuit. The diodes still check out, with D652 (and others) giving
readings of ~0.65-0.65 on my multimeter. However, only diode D672 gave a
reading of 0.041 on two different multimeters, so I suspect this one is
bad. This one is connected to the +12.6 V circuit.

As for resistors, some also seem to have issues, with R692 (going to V692)
being at 1.4-1.5 ohm, but it is supposed to be 4.3 ohm. I admit I am having
a bit of difficulty in locating R659, so I was unable to confirm if that
one is okay.

Once the fuses come in, I'll let you know how the voltages read out.
However, as for the burning, think it may be coming from the wires leading
to the T601 (see the photo: https://goo.gl/photos/SvfUM7r7w2VY3zsN8
https://goo.gl/photos/SvfUM7r7w2VY3zsN8)


- Evan

[Non-text portions of this message have been removed]


Evan
 

1. For the diodes, those values are from my multimeter in diode testing mode, but it does not display any units associated with the reading (so I am assuming it is in volts).

4. C614 gives a resistance of 3.2 ohm, so it would seem that it checks out.


I also checked the burnt black stuff on the wires, which did peal off with some isopropanol. It appears to be just melted plastic, and it is not from the yellow wire (since that was clean underneath). As such, the burning smell may have just been old plastic and dust from various loose components that were not cleaned off initially (for example, the rubber casing around the CRT connector has basically dried and disintegrated at this point).



As for the -3000 V supply to pin 5 on T601, it gave a resistance of ~4.40 M-Ohm (my multimeter reads up to 20 M-Ohm, so it should be accurate).


With the video, the only thing with V659 was that it was flickering on and off (which is accurate in the video no matter the angle), although it is difficult to make out the behavior of V620. Again, the issue that I observed with that was just the blue electron streams around the sides of the wall, and then the redness at the center of the metal plate in the tube.


I won't be doing any voltage testing until the new fuses come in, and they are the correct type (1.25 A, Slo-Blo), so nothing to worry about with the dangers of higher rated fuses. I do not have any AFCI or GFCI outlets available unfortunately, so I will just be very careful in the live testing once I get to that point. However, I will be sure to check what I plan on doing here before proceeding, since I definitely do not want to fry anything (or myself for that matter).


- Evan

Dave Casey
 

Sounds good. There may actually be a problem with D672, and you can do some
easy checks to further verify that. The +12.6V supply is used for the
heaters of the input amplifiers (the first amplification stage your input
signal goes through). While the other tubes are heated with AC from a
transformer winding, these are heated with DC for the sake of reduced
noise. Your scope has two possible configurations:
1. The earlier style where the input tubes are V334 and V434, (two 6DJ8s).
2. The later style where the input tubes are V334, V434, V344, and V444
(four 8393s). The 8393 is a late-to-the-party kind of tube called a
Nuvistor, and it's in a small metal can instead of a big glass bulb.

In either case, the +12.6V supply should still be feeding the heaters of
these tubes.

You might re-check D672 with all two (or four, depending on the above)
tubes removed from their sockets and see if it looks more like the others
than it did in your previous round of measurements.

With those tubes removed, you have also broken the return current path for
the +12.6V supply. This means you can also test the D672 using the ohmmeter
function of your multimeter without having to unsolder it. To do this, with
those particular tubes we're talking about removed, measure the resistance
across D672, then reverse your test leads and repeat the measurement. You
should get two very different measurements. When the positive lead of your
meter is on the "pointy" side of the diode's arrow, you should see an open
circuit (greater than 20M ohm). If you do not, then either the diode is not
a diode anymore, or one of the filtering capacitors after the diode (C652c
and C654c) is bad. Because of the capacitors, you may initially see a very
low resistance measurement that steadily increases until it exceeds the
range of your meter. This is normal and is just your meter charging up
those capacitors.

There is only one other place I see the 12.6V rail being used, and that is
to bias the heaters of the other tubes (also a noise reduction technique).
This is on the power supply schematic next to T601 pins 10 and 11. R605 is
going to do a pretty good job of not letting a fault in that part of the
scope overload the 12.6V supply, and you can get a fairly decent
measurement of R605 in circuit (if anything, it has probably drifted higher
than 47k, which shouldn't hurt anything).

With the test leads reversed (positive lead of the meter on the T620
transformer side of the diode), you should see some finite resistance, even
as high as tens of kilo-ohms (depends on the diode and the meter).

Obviously all this is still to be done with the scope unplugged. (Yes, roll
your eyes, but I'm going to remind you every time. And you should hold the
loose plug in your hand every time before you reach into that chassis; it's
a good habit that can save you from making a careless mistake.) It is also
a good idea to keep track of which tube came from which socket and put them
back like you found them. Mixing them up will affect the calibration of the
instrument (or what's left of it after all these years sitting). If you mix
up the tubes you may or may not be able to tell the difference when the
scope is working again, but it shouldn't make or break operation of the
scope (unless one of them is bad).

While they're removed, it's a good time to check each of those two (or
four) tubes for a shorted filament (heater). A shorted filament would cause
an increased load on the 12.6V supply, possibly causing all the other power
supply problems you're seeing, including the blown fuse.

Regarding GFCI - you can rather inexpensively get an add on GFCI that plugs
into the wall and provides a protected outlet. They are sold at home
improvement/hardware stores. At this point, the power switch wiring is no
longer much of a suspect since that wiring didn't actually burn, but if it
were a problem, a GFCI would trip right away and let you know.


Dave Casey

On Thu, Apr 6, 2017 at 2:58 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



1. For the diodes, those values are from my multimeter in diode testing
mode, but it does not display any units associated with the reading (so I
am assuming it is in volts).

4. C614 gives a resistance of 3.2 ohm, so it would seem that it checks
out.


I also checked the burnt black stuff on the wires, which did peal off with
some isopropanol. It appears to be just melted plastic, and it is not from
the yellow wire (since that was clean underneath). As such, the burning
smell may have just been old plastic and dust from various loose components
that were not cleaned off initially (for example, the rubber casing around
the CRT connector has basically dried and disintegrated at this point).



As for the -3000 V supply to pin 5 on T601, it gave a resistance of ~4.40
M-Ohm (my multimeter reads up to 20 M-Ohm, so it should be accurate).


With the video, the only thing with V659 was that it was flickering on and
off (which is accurate in the video no matter the angle), although it is
difficult to make out the behavior of V620. Again, the issue that I
observed with that was just the blue electron streams around the sides of
the wall, and then the redness at the center of the metal plate in the
tube.


I won't be doing any voltage testing until the new fuses come in, and they
are the correct type (1.25 A, Slo-Blo), so nothing to worry about with the
dangers of higher rated fuses. I do not have any AFCI or GFCI outlets
available unfortunately, so I will just be very careful in the live testing
once I get to that point. However, I will be sure to check what I plan on
doing here before proceeding, since I definitely do not want to fry
anything (or myself for that matter).


- Evan


[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]

 

@Evan,
As such, I only now have gotten time to focus on the scope.
No autofocus on this oldie then?

Seriously, what wonderful condition! Well worth repairing!

Raymond

 

Evan:

I'm just now checking emails (about 12 hours after your post, reproduced below) and I see that several other Tekscopes group members have already offered some good suggestions and advice. Since you indicate you have now blown a fuse, I will offer a suggestion for the initial "power up" test once you have some replacement fuse(s). Hopefully you are purchasing a "few" replacement fuses (perhaps a half-dozen or so?) as you might wind up going through some of them during tests...

Assuming that the various "power off" tests that you preform don't indicate a "smoking gun" failed component- When you do get a replacement fuse and go to re-energize the scope, here's my recommendation: Before flipping the power switch to "on", connect a DC voltmeter to the positive terminal of C612 [this is also the cathode of D612; it is the +500 VDC unregulated bus]. You should read zero voltage (since power is off) but if you do not, first discharge this point to bring the residual capacitance charge of the +500 VDC bus down to zero. Then remove tubes V620 and V634. To remove V620, you will need to first remove the plate cap at V620, which is connected to the +500 VDC bus [which is why I suggest verifying the discharge of the +500 VDC bus before possibly touching the plate cap].

Leaving the voltmeter connected to the +500 VDC bus connection point, now try to power up the oscilloscope. At this point, hopefully the fuse does not blow and you can measure a voltage of about 540 to 550 volts on the nominal +500 VDC bus. Leave the scope connected in this fashion and powered up for 5 or 10 minutes. If this goes as planned, then the power supply up to the +500 VDC bus is probably OK (although a winding-to-frame short of the CRT filament winding in T601 is still a likely possibility). Measured voltage on the nominal +500 VDC bus will likely be considerably higher than 500.0 volts because without V620 and V634, there's no load on the +500 volt bus, as there's no current draw from the +500 volt bus into T620 with these tubes pulled. Whatever voltage you measure at the +500 VDC bus with power "on", it should be rock-steady. Also, in your original post from several days ago, you mentioned a "buzzing" sound. Is the sound still present? Now turn the scope power "off" and observe that the +500 VDC bus voltage takes a long time to decay to zero (probably several tens of minutes) and keep this in mind as you proceed further- the filter capacitors can take a LONG time to discharge.

Let us know what has happened during these tests. Did the fuse blow, and if so, after how long? Audible noise? Voltage reading, and stability, at the +500 VDC bus?

Running this test with V620 and V634 removed serves to "mostly" disconnect the 25 khz power conversion circuitry and T620.

Assuming that the fuse does NOT open during this test, then the next step (in my opinion) is with scope power "off", connect a voltmeter to the -100 VDC bus (leave the original voltmeter connected to the +500 VDC bus if you have two voltmeters available), plug in tubes V620 and V634, and power the scope back up. I suspect that the fuse may "blow" under these conditions; let us know what happens. As done earlier, measure the -100 VDC bus level and it's stability (analog voltmeter preferred for this determination). Observe if there's any audible noise, smoke, etc.

Also, I looked back over my notes of how I researched failures on the Tekscopes yahoo group- do a "conversations" search on "Tek RM 503 troubleshoot" for a bunch of emails from November 2010 that might be relevant to your situation.

Mike Dinolfo N4MWP

On 04/06/2017 01:02 AM, enchanter464@... [TekScopes] wrote:


Hello all,

I feel bad that it has been several days since my last posting.
Unfortunately, my work is at a standstill right now. Over the past
weekend I had focused most of my work on restoring a vintage volt meter
(Triplett 630-A), which is now working (and supports up to 6000 V,
although I lack the HV leads, so no -3000 V testing yet). As such, I
only now have gotten time to focus on the scope.

However, when I connected the leads to the ground (chassis) and -100 V
test point, plugged in the scope, and after the brief burning smell,
nothing happened (no lights for the scope, no CRT turning on, no tubes
activating). I discovered that the fuse had blown during my attempt to
get the voltages, but after no luck in going through my fuse stock, I
ended up having to order a set of new ones to come in, so that won't be
until next week earliest.

For the scope, I was still able to check the non-voltage components on
the power circuit. The diodes still check out, with D652 (and others)
giving readings of ~0.65-0.65 on my multimeter. However, only diode D672
gave a reading of 0.041 on two different multimeters, so I suspect this
one is bad. This one is connected to the +12.6 V circuit.

As for resistors, some also seem to have issues, with R692 (going to
V692) being at 1.4-1.5 ohm, but it is supposed to be 4.3 ohm. I admit I
am having a bit of difficulty in locating R659, so I was unable to
confirm if that one is okay.

Once the fuses come in, I'll let you know how the voltages read out.
However, as for the burning, think it may be coming from the wires
leading to the T601 (see the photo:
https://goo.gl/photos/SvfUM7r7w2VY3zsN8
https://goo.gl/photos/SvfUM7r7w2VY3zsN8)


- Evan


Evan
 

Hi everyone,

I just got in today the fuses and GFCI adapter (just in case), so I went ahead with the powered-off tests first.


My scope is one of the earlier models, having V334 and V434 both as 6DJ8 tubes. I confirmed on both tubes that the heating filaments are good (V334 gave a resistance of 2.7-2.8 Ohm, and V434 gave a resistance of 2.8-2.9 Ohm). With the two tubes removed, I retested D672, which gave similar readings this time to the other diodes on the power circuit (with a diode testing reading of +0.637 V, or a resistance of greater than 20 M-Ohm).


However, I am unsure on R605, which gave a reading of 111.5 k-Ohm (instead of 47 k). The resistors ahead of this from T601 leads 10 and 11, R606 and R607, both gave readings of 51.2 ohm, which is less than their 100 ohm specification. I am not sure if this is just a reading error since they are all soldered together, or if they could be to blame for the observed issues.


I would proceed with the power-on testing (having removed V620 and V634), but I have not been able to locate the +500 VDC bus. My manual only shows the points to connect for the +250, +100, +12.5, -100, and -3000 V points for testing, but not the 500 V or 85 V ones. Would someone be able to point me to the right direction for this test? (It is late right now, so I will hold off until tomorrow to actually run the tests).


Also, a side question, but in the manual, the test setup shown has the oscilloscope plugged into a Variac for power. Is this suggested / has a purpose? (I do have one that I can use)


- Evan

Dave Casey
 

Evan -

R605 is high, but it is not likely to cause any significant problems. R606
and R607 are effectively paralleled in circuit because of the low
resistance of the 6.3V winding on T601, so the measured value is
reasonable. (Basic circuit theory here for combining discrete circuit
elements: Requivalent = R1*R2/(R1+R2) = 100*100/200 = 100/2 = 50 ).

With V20 and V634 removed, you can get readings of the 500V bus at D612 or
either side of R626. Be sure to follow the advice others have given before
about making sure the charge on this bus has dissipated before contacting
it. Regardless of whether or not the tubes are still installed, you should
see the resistance to ground steadily climb until reaches about 300k (more
if you're on the far side of R626). If it is less than that something's not
right, probably with C611/C612, D611/D612, or R611/R612.

The +85V bus can be measured at the socket of V659. If you look at the back
of the socket, you will see only three pins are actually connected. Two are
tied together; these are pins 1 and 5 and are the +85V bus. If you look
closely, you will see pin 2 is the only other connected pin, and it is tied
straight to the chassis ground.

A variac lets you do several things. The manual is showing it used to
adjust the input line voltage to exactly 117VAC for the purpose of precise
measurements or calibration. But the variac is also a useful
troubleshooting tool. It allows you to ramp up the voltage slowly, and do
sanity checks along the way. For example, if you have a failing filter
capacitor such as C611 or C612, you could use the variac to supply only 10%
of the nominal supply voltage and expect to see 10% of the expected no-load
output voltage on the +500V bus. At this point, leaky capacitors wouldn't
be stressed as much because they're not near their rated voltage. You can
expect the +500V bus (with V620 and V634 removed) to linearly track the
variac setting. If you observe a non-linearity, then it's possible that the
diodes or capacitors are leaking at higher voltages.

Keep in mind also that the GFCI only protects you on the input side of the
T601 power transformer. It's like wearing a helmet - it makes what you're
doing safer, but you shouldn't expect it to make you completely safe. The
+500V supply will still kill you even with the GFCI.

Dave Casey

On Thu, Apr 13, 2017 at 12:09 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



Hi everyone,

I just got in today the fuses and GFCI adapter (just in case), so I went
ahead with the powered-off tests first.


My scope is one of the earlier models, having V334 and V434 both as 6DJ8
tubes. I confirmed on both tubes that the heating filaments are good (V334
gave a resistance of 2.7-2.8 Ohm, and V434 gave a resistance of 2.8-2.9
Ohm). With the two tubes removed, I retested D672, which gave similar
readings this time to the other diodes on the power circuit (with a diode
testing reading of +0.637 V, or a resistance of greater than 20 M-Ohm).


However, I am unsure on R605, which gave a reading of 111.5 k-Ohm (instead
of 47 k). The resistors ahead of this from T601 leads 10 and 11, R606 and
R607, both gave readings of 51.2 ohm, which is less than their 100 ohm
specification. I am not sure if this is just a reading error since they are
all soldered together, or if they could be to blame for the observed
issues.


I would proceed with the power-on testing (having removed V620 and V634),
but I have not been able to locate the +500 VDC bus. My manual only shows
the points to connect for the +250, +100, +12.5, -100, and -3000 V points
for testing, but not the 500 V or 85 V ones. Would someone be able to point
me to the right direction for this test? (It is late right now, so I will
hold off until tomorrow to actually run the tests).


Also, a side question, but in the manual, the test setup shown has the
oscilloscope plugged into a Variac for power. Is this suggested / has a
purpose? (I do have one that I can use)


- Evan

[Non-text portions of this message have been removed]


Daniel Koller
 

Evan,
   To follow up on the advice of others...  Be VERY careful with those high voltage supplies!!!  I hit the 500V supply in a Tek 545 with a finger once and I still remember that afternoon clearly, and I am lucky because I remember it.  It's good practice to keep one hand in a pocket when contacting a probe to the HV points.  Also NEVER work barefoot, and I would also add, it's best not to work on the power supplies late at night when you are tired.
  Two of the more common failures of this scope relate to the HV, so if you have a steady beam or spot on the CRT, your scope is likely fixable. 

  Considering the arcing sound you mentioned a while back, it might be a good Idea to locate the HV rectifier filament winding on the main transformer and unsolder the filament leads.  Then measure the resistance of that winding to ground and to the input windings.  It should be very high, unless it was arcing inside the transformer.
   If the arcing continues, I would not leave the scope on for very long - something is possibly burning up.  But one thing you could do is stick some rubber tubing on the end of a plastic straw.  Stick on end of the tube in an ear and use the end of the straw to probe around the scope, listening for the arc - a diy stethoscope if you will.   That should help you locate the source of the noise.

  I haven't been following your thread too closely so some of my advice has probably already been given by others.  Good luck!
Dan

On Thursday, April 13, 2017, 2:45:19 AM EDT, Dave Casey polara413@... [TekScopes] <TekScopes@...> wrote: 
Evan -

R605 is high, but it is not likely to cause any significant problems. R606
and R607 are effectively paralleled in circuit because of the low
resistance of the 6.3V winding on T601, so the measured value is
reasonable. (Basic circuit theory here for combining discrete circuit
elements: Requivalent = R1*R2/(R1+R2) = 100*100/200 = 100/2 = 50 ).

With V20 and V634 removed, you can get readings of the 500V bus at D612 or
either side of R626. Be sure to follow the advice others have given before
about making sure the charge on this bus has dissipated before contacting
it. Regardless of whether or not the tubes are still installed, you should
see the resistance to ground steadily climb until reaches about 300k (more
if you're on the far side of R626). If it is less than that something's not
right, probably with C611/C612, D611/D612, or R611/R612.

The +85V bus can be measured at the socket of V659. If you look at the back
of the socket, you will see only three pins are actually connected. Two are
tied together; these are pins 1 and 5 and are the +85V bus. If you look
closely, you will see pin 2 is the only other connected pin, and it is tied
straight to the chassis ground.

A variac lets you do several things. The manual is showing it used to
adjust the input line voltage to exactly 117VAC for the purpose of precise
measurements or calibration. But the variac is also a useful
troubleshooting tool. It allows you to ramp up the voltage slowly, and do
sanity checks along the way. For example, if you have a failing filter
capacitor such as C611 or C612, you could use the variac to supply only 10%
of the nominal supply voltage and expect to see 10% of the expected no-load
output voltage on the +500V bus. At this point, leaky capacitors wouldn't
be stressed as much because they're not near their rated voltage. You can
expect the +500V bus (with V620 and V634 removed) to linearly track the
variac setting. If you observe a non-linearity, then it's possible that the
diodes or capacitors are leaking at higher voltages.

Keep in mind also that the GFCI only protects you on the input side of the
T601 power transformer. It's like wearing a helmet - it makes what you're
doing safer, but you shouldn't expect it to make you completely safe. The
+500V supply will still kill you even with the GFCI.

Dave Casey

On Thu, Apr 13, 2017 at 12:09 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



Hi everyone,

I just got in today the fuses and GFCI adapter (just in case), so I went
ahead with the powered-off tests first.


My scope is one of the earlier models, having V334 and V434 both as 6DJ8
tubes. I confirmed on both tubes that the heating filaments are good (V334
gave a resistance of 2.7-2.8 Ohm, and V434 gave a resistance of 2.8-2.9
Ohm). With the two tubes removed, I retested D672, which gave similar
readings this time to the other diodes on the power circuit (with a diode
testing reading of +0.637 V, or a resistance of greater than 20 M-Ohm).


However, I am unsure on R605, which gave a reading of 111.5 k-Ohm (instead
of 47 k). The resistors ahead of this from T601 leads 10 and 11, R606 and
R607, both gave readings of 51.2 ohm, which is less than their 100 ohm
specification. I am not sure if this is just a reading error since they are
all soldered together, or if they could be to blame for the observed
issues.


I would proceed with the power-on testing (having removed V620 and V634),
but I have not been able to locate the +500 VDC bus. My manual only shows
the points to connect for the +250, +100, +12.5, -100, and -3000 V points
for testing, but not the 500 V or 85 V ones. Would someone be able to point
me to the right direction for this test? (It is late right now, so I will
hold off until tomorrow to actually run the tests).


Also, a side question, but in the manual, the test setup shown has the
oscilloscope plugged into a Variac for power. Is this suggested / has a
purpose? (I do have one that I can use)


- Evan




[Non-text portions of this message have been removed]


#yiv7263641876 #yiv7263641876 -- #yiv7263641876ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv7263641876 #yiv7263641876ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv7263641876 #yiv7263641876ygrp-mkp #yiv7263641876hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv7263641876 #yiv7263641876ygrp-mkp #yiv7263641876ads {margin-bottom:10px;}#yiv7263641876 #yiv7263641876ygrp-mkp .yiv7263641876ad {padding:0 0;}#yiv7263641876 #yiv7263641876ygrp-mkp .yiv7263641876ad p {margin:0;}#yiv7263641876 #yiv7263641876ygrp-mkp .yiv7263641876ad a {color:#0000ff;text-decoration:none;}#yiv7263641876 #yiv7263641876ygrp-sponsor #yiv7263641876ygrp-lc {font-family:Arial;}#yiv7263641876 #yiv7263641876ygrp-sponsor #yiv7263641876ygrp-lc #yiv7263641876hd {margin:10px 0px;font-weight:700;font-size:78%;line-height:122%;}#yiv7263641876 #yiv7263641876ygrp-sponsor #yiv7263641876ygrp-lc .yiv7263641876ad {margin-bottom:10px;padding:0 0;}#yiv7263641876 #yiv7263641876actions {font-family:Verdana;font-size:11px;padding:10px 0;}#yiv7263641876 #yiv7263641876activity {background-color:#e0ecee;float:left;font-family:Verdana;font-size:10px;padding:10px;}#yiv7263641876 #yiv7263641876activity span {font-weight:700;}#yiv7263641876 #yiv7263641876activity span:first-child {text-transform:uppercase;}#yiv7263641876 #yiv7263641876activity span a {color:#5085b6;text-decoration:none;}#yiv7263641876 #yiv7263641876activity span span {color:#ff7900;}#yiv7263641876 #yiv7263641876activity span .yiv7263641876underline {text-decoration:underline;}#yiv7263641876 .yiv7263641876attach {clear:both;display:table;font-family:Arial;font-size:12px;padding:10px 0;width:400px;}#yiv7263641876 .yiv7263641876attach div a {text-decoration:none;}#yiv7263641876 .yiv7263641876attach img {border:none;padding-right:5px;}#yiv7263641876 .yiv7263641876attach label {display:block;margin-bottom:5px;}#yiv7263641876 .yiv7263641876attach label a {text-decoration:none;}#yiv7263641876 blockquote {margin:0 0 0 4px;}#yiv7263641876 .yiv7263641876bold {font-family:Arial;font-size:13px;font-weight:700;}#yiv7263641876 .yiv7263641876bold a {text-decoration:none;}#yiv7263641876 dd.yiv7263641876last p a {font-family:Verdana;font-weight:700;}#yiv7263641876 dd.yiv7263641876last p span {margin-right:10px;font-family:Verdana;font-weight:700;}#yiv7263641876 dd.yiv7263641876last p span.yiv7263641876yshortcuts {margin-right:0;}#yiv7263641876 div.yiv7263641876attach-table div div a {text-decoration:none;}#yiv7263641876 div.yiv7263641876attach-table {width:400px;}#yiv7263641876 div.yiv7263641876file-title a, #yiv7263641876 div.yiv7263641876file-title a:active, #yiv7263641876 div.yiv7263641876file-title a:hover, #yiv7263641876 div.yiv7263641876file-title a:visited {text-decoration:none;}#yiv7263641876 div.yiv7263641876photo-title a, #yiv7263641876 div.yiv7263641876photo-title a:active, #yiv7263641876 div.yiv7263641876photo-title a:hover, #yiv7263641876 div.yiv7263641876photo-title a:visited {text-decoration:none;}#yiv7263641876 div#yiv7263641876ygrp-mlmsg #yiv7263641876ygrp-msg p a span.yiv7263641876yshortcuts {font-family:Verdana;font-size:10px;font-weight:normal;}#yiv7263641876 .yiv7263641876green {color:#628c2a;}#yiv7263641876 .yiv7263641876MsoNormal {margin:0 0 0 0;}#yiv7263641876 o {font-size:0;}#yiv7263641876 #yiv7263641876photos div {float:left;width:72px;}#yiv7263641876 #yiv7263641876photos div div {border:1px solid #666666;height:62px;overflow:hidden;width:62px;}#yiv7263641876 #yiv7263641876photos div label {color:#666666;font-size:10px;overflow:hidden;text-align:center;white-space:nowrap;width:64px;}#yiv7263641876 #yiv7263641876reco-category {font-size:77%;}#yiv7263641876 #yiv7263641876reco-desc {font-size:77%;}#yiv7263641876 .yiv7263641876replbq {margin:4px;}#yiv7263641876 #yiv7263641876ygrp-actbar div a:first-child {margin-right:2px;padding-right:5px;}#yiv7263641876 #yiv7263641876ygrp-mlmsg {font-size:13px;font-family:Arial, helvetica, clean, sans-serif;}#yiv7263641876 #yiv7263641876ygrp-mlmsg table {font-size:inherit;font:100%;}#yiv7263641876 #yiv7263641876ygrp-mlmsg select, #yiv7263641876 input, #yiv7263641876 textarea {font:99% Arial, Helvetica, clean, sans-serif;}#yiv7263641876 #yiv7263641876ygrp-mlmsg pre, #yiv7263641876 code {font:115% monospace;}#yiv7263641876 #yiv7263641876ygrp-mlmsg * {line-height:1.22em;}#yiv7263641876 #yiv7263641876ygrp-mlmsg #yiv7263641876logo {padding-bottom:10px;}#yiv7263641876 #yiv7263641876ygrp-msg p a {font-family:Verdana;}#yiv7263641876 #yiv7263641876ygrp-msg p#yiv7263641876attach-count span {color:#1E66AE;font-weight:700;}#yiv7263641876 #yiv7263641876ygrp-reco #yiv7263641876reco-head {color:#ff7900;font-weight:700;}#yiv7263641876 #yiv7263641876ygrp-reco {margin-bottom:20px;padding:0px;}#yiv7263641876 #yiv7263641876ygrp-sponsor #yiv7263641876ov li a {font-size:130%;text-decoration:none;}#yiv7263641876 #yiv7263641876ygrp-sponsor #yiv7263641876ov li {font-size:77%;list-style-type:square;padding:6px 0;}#yiv7263641876 #yiv7263641876ygrp-sponsor #yiv7263641876ov ul {margin:0;padding:0 0 0 8px;}#yiv7263641876 #yiv7263641876ygrp-text {font-family:Georgia;}#yiv7263641876 #yiv7263641876ygrp-text p {margin:0 0 1em 0;}#yiv7263641876 #yiv7263641876ygrp-text tt {font-size:120%;}#yiv7263641876 #yiv7263641876ygrp-vital ul li:last-child {border-right:none !important;}#yiv7263641876

Evan
 

Ok. So I have a lot of measurements to report:

1. For the 500 V bus test, with V620 and V634 removed, I first checked the two tubes. V620 (6DQ6B) gave a heater resistance (pins 2 and 7) of 0.9 Ohm (very low), while V634 (6DJ8) gave a heater resistance of 2.1 Ohm, same as the other 6DJ8 tubes. Also of note, on V620, there was visible scorching/blackness at the base of the metal components.


For the voltage testing with the new fuse in place, the 500 V bus registered at ~560 V on the analog meter, and +566-567 V on my digital multimeter, which was constant over 10 minutes of being turned on (with the two tubes removed). There was no noise, burning smell, or any activity from the tubes. Stability-wise, the voltage only increased by +1V over the 10 minute period, and no fuse blown.




2. With the tubes back in, using the analog volt meter:


a.) At the -100 V bus, it only gave a voltage from -25 V to -50 V (fluctuating back and forth around -55 V, and steadily decreasing until around -25 V). There was a buzzing sound and flickering again from V692, and smell of burning from V620, which got very hot around the tube, and smell/heat lingered even while the scope discharged unplugged.


b.) At the +500 V, the voltage ramped up to 560 V, and then decreased to 500 V once V692 kick on (and began to buzz), but was steady.


c.) At the +12.6 V bus, voltage fluctuated around 5.2 V, going as low as 4.0 V, but shooting up to around 8.6 V when V692 made sputtering sounds.


d.) At the +100 V bus, voltage was at 55 V, fluctuating between 50 V and 58 V, with spikes at 63 V.


e.) At the +250 V bus, voltage fluctuated around 150 V, going as low as 125 V (when V692 make sputtering sounds), and as high as 160 V.


f.) Lastly, the +85 V bus fluctuated around 90 V, dipping down to around 70 V, and spiking up to 110 V.




For all of the above readings, since V620 was showing signs of burning, I only had the scope on for less than a minute (once V692 warmed up), discharging off between each test. In addition, I did not check the -3000 V bus since I do not have appropriate leads to test such high voltage.


At this point, is this still likely a transformer issue, and if so, what do you suggest on how to further assess the scope?


- Evan