Date   
Re: AF501 woes

EJP
 

I've posted a photo album here about this entitled 'AF501 trigger problem'.

The photos show the AF501 trigger output when driven by a sine wave from an FG502, with the scope sync-ed to the FG502 trigger output. The AF501 was in Narrow Filter mode, frequency 19 x 1000x, unity gain. The picture sequence got reversed during the upload. They now are:

1. 32kHz, medium level: 1/2-height spuria.
2. 30kHz, medium level: 1/2-height spuria.
3. 35kHz, medium level: no spuriae.
4. 25kHz, medium level: full-height spuria.
5. 19kHz, minimum level: full-height spuria.
6. 19kHz, medium level: no spuriae.

'Level' refers to FG502 output level. It will be seen that the spuria when present is at the 2nd-harmonic frequency. There is no problem in (3) and (6); there is a half-sized problem in (1) and (2); and a full-sized problem in (4) and (5). This sample shows that the problem is both level- and frequency-dependent. The spuriae change height continuously with both level and frequency; i.e. it is a continuous rather than stepwise problem. The spuriae get significant enough at some settings to disturb a digital counter into showing double the correct frequency.

I've checked the output of the comparator U290 and it doesn't exhibit any such anomalies at any frequency or level setting.

Being a jelly-bean part, I changed Q298 for a new 2N3904 and it moved the frequency of onset away from the setting at (6), which is the one of current interest to me, so actually I don't have an immediate problem any more. I then changed Q306 for another 2N3904 as I now had them in hand, but it didn't change anything. It seems reasonable to continue along this line and change the Darlington Q302, if I can find a 2N5305 or equivalent.

All comments and advice welcome.

EJP

Re: 475a no trace

whitevamp .
 

ohh umm sorry its 0.214 volts not mv.
looked at the meter/wrote it down wrong, just went and reproduced the short and remeasured it and yes its 0.214v.

and yes there is a short in the load its the board to board interconnect when seated all the way down it shorts out, but when lifted ever so slightly its not shorted.
between the sweep and Z logic board, and the main board/power supply board.

still haven't figured out why its shorting out like that.


________________________________
From: TekScopes@... <TekScopes@...> on behalf of David @DWH [TekScopes] <TekScopes@...>
Sent: Saturday, April 29, 2017 12:42 PM
To: TekScopes@...
Subject: Re: [TekScopes] 475a no trace



Um, 0.214 millivolts or 0.214 volts? If the former then the regulator
has a problem and if the later, then there is a short in the load
somewhere.

I did not work out the numbers but Tektronix usually set the fold-back
current limit to 1/2 of the maximum output current which is consistent
with 0 volts output at 0.358 amps.

On Wed, 26 Apr 2017 07:03:40 +0000, you wrote:


ohh and the voltage across R1468 was 0.214mv and if my math is correct that equates to 0.358ma.

hence why i was chasing tant's and checking every thing.

New member's first post (forwarded by Dennis Tillman)

 

This new member (Christopher Kuni) is having trouble posting messages at the
moment so I am forwarding his first message to the group for him.

Dennis Tillman W7PF



---

Hello Tek group.

Regarding the request for bio info, I’ve been interested in circuit design
and troubleshooting since high school in the early 60s. My first Tek scope
was a 511 or 513, I don’t remember which, a freebie in about 1980. A few
years later I bought a pristine 2215 at a hamfest for $700 when that price
was a bargain for a 2215. The 2215 is still in frequent use and serves my
purposes except for bandwidth; hence my recent acquisition of two
non-working 485s for restoration.

I’ve got one of them working perfectly. The other is close, but the
remaining problem baffles me, and I hope group members can help. Square wave
leading edge and corner optimization is impossible. See photos. The leading
edge doesn’t quite make it to the upper level of the square wave, and there
is a subsequent sag before the trace finally settles at the upper level.
These phenomena are in the first few nanoseconds of the waveform. The
problem exists in both channels, so I assume the cause is not in the earlier
stages where the channel signals are separate. No adjusting of corner or
flat top trimmers anywhere in the vertical amplifier cures the distortion.
The trace is excellent on the other 485, so I doubt the trouble is in the
pulser.

I’ve checked many components and voltages in the vertical amp; all are
normal. Bridging known good caps across the bypass caps has no effect. I see
no signal riding on any supply lines. The continuity and insulation of the
delay line test good with a multimeter. The switching circuitry for the
20Mhz bandwidth limiter including the panel switch functions normally
(defects there caused somewhat similar distortion in the other 485). Probing
the board with my finger, I get the most change in the distortion when
touching wiring between U620 and U650.

Any ideas? Is it time to buy new ICs, such as U620 and U650 (can’t rob them
from the other 485, as the manual specifies different part numbers for that
newer scope)?

Now I’ll try to post photos of the traces.

Thanks in advance for any suggestions.

Christopher Kuni
KØMGP
Portland OR





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

Email re. Tucker closing...no affiliation....might be of interest to group

chipbee40
 

Quote:
Possible Last Month for eBay Listings, Please make Offers, Business for Sale!

At this time, it appears our eBay listings will probably be discontinued by the end of May. Our Business is for Sale and we welcome any serious inquiries.

We have changed the majority of our 20,000 listings to allow you to make offers (Reasonable Offers Please). Our prices are already discounted with most items on sale at 20% off. We still have a lot of manuals and parts to sell. This may be your last opportunity to buy some of the rare manuals.

Parts Promotion: We have over 600 listings with some 10,000 parts priced between $1 and $10 each. We would like to sell these and are offering a 60% discount this week.
You total order must be $25 or more to qualify. You just need to make offers on the parts of interest at that discount price and we will accept the offers. We have not changed the basic prices of the parts. This will be a regular eBay transaction.

It is easy to find these parts if you go to our eBay store (click the Blue emblem) and find “OTHER” in the menu of categories. If you do a sort of cost the $1 items should appear first. Call us at 2143488800 if you have a problem.

PROMOTIONS on eBay this week for equipment:
Sorensen Xantrex XTQ15151530 Quad Power Supply $160 each, Listing 391512005815

Sorensen Xantrex XTT15-4 Triple Power Supply, $130 each, Listing 391512060604

Agilent 6031A DC Power Supply, 0-20V, 0-120A, 1000 W, manual, tested units, only 2 left. Regular price of $750. This week priced at only $450 + shipping. Listing no. 391745719736

TEKTRONIX P5205 HIGH VOLTAGE DIFFERENTIAL PROBE WITH ALL ACCESSORIES, TESTED.
REGULAR PRICE IS $550. THIS WEEK PRICED TO SELL FOR $355. LISTING NO. 302207795886.

Large Website Discounts:
Our 50%+ discount on Website Purchases at www.etestmanuals.com http://na02.mypinpointe.com/link.php?M=48212268&N=48649&L=22673&F=H and www.etestparts.com http://na02.mypinpointe.com/link.php?M=48212268&N=48649&L=22672&F=H continues this week Please send me lists by email and I will evaluate pricings and combined shipping costs. I can send you spreadsheets of these two sites if that would be helpful.Please send to jtucker@... mailto:jtucker@....
The pricing and shipping costs are erratic and not updated on these two sites. We can be more aggressive in pricing on these sites and they have a great deal more listings than eBay. In some cases, we make greater than 50% discounts.

BULK MANUAL PURCHASES:
We still need to make some large sales and are offering several possibilities. One is your choice of 40 manuals at $25 each. Another is your choice of 100 manuals at $11 each. Another is your choice of 1000 manuals for $6 each. Shipping is extra but we will combine to get cheapest rates.

We can send you PayPal invoices for any purchases not done on eBay or the two Websites. In all cases you still have the protection of PayPal. Our phone number is 2143488800. We prefer email as most questions about manuals require research and can’t be handled in a phone call. During this time, we will look at email 7 days per week and process orders at least 6 days per week.

We will be forced to move at the end of May and will likely discontinue eBay listings
We would like to sell as much as we can before then.

Thanks again for your business and we look forward to hearing from you soon.

Jim Tucker
Tucker Electronics
11448 Pagemill Road
Dallas, Texas 75243

jtucker@...
2143488800

Re: FG504 died - Now fixing

Jerry Massengale <jmassen418@...>
 

BRAVO!

On Mon, May 1, 2017 at 6:15 PM, Joe Laffey joe@... [TekScopes] <
TekScopes@...> wrote:



After much further troubleshooting, lifting legs and testing things I was
able to nail down the source of my 6-10 Ohm short across the +15V rail. It
wasn't any of the poor capacitors and diodes that got their legs
unwillingly lifted.

It turns out it was Occam's Razor... literally slicing a wire!

One of the wires connected to the Symmetry switch/pot combo was rubbing up
against another metal contact on that switch combo. It had worn through
the insulation and was making contact. I guess it was heat expansion that
caused it to fail when left on for a while.

So I am a happy man with my FG504 working smoothly again. It is such a
nice little generator. 40MHz analog.

--
73
Joe Laffey


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

2430A Troubleshooting

Peter Crary
 

Hello,
First, I will introduce myself. I am a sophomore in high school and enjoy working with and repairing ham radios and the complementary test equipment. I have a 2225 and a TDS744A that are functional, along with two 2430A's and a 485 that are not operational.
Currently, I am working on the 2430A's. When I purchased them, one had visible damage to the processor board from the backup battery that had leaked. Several components and component legs were missing or heavily corroded. When powered on, none of the panel LED's or CRT showed any activity. I haven't investigated the severity of the damage, but I presume that some inner layers have been damaged. The second powers on, and shows a single point on the right of the CRT. The GPIB status LED's stay lit, and the trigger LED's do flash throughout the boot cycle. I've been through the service manual and decoded the trigger LED's as displaying code "3102", a fault with the display memory. After a few more flashes of the LED's and some brief activity on the CRT, the scope reboots. I have checked the operation of the system processor, as per the service manual, and all seems well. When I replace the display board for the one in the other scope, the same symptoms occur. Same if I put this processor board in the other scope. Unless both display boards have the exact same fault, it has to be an issue with the processor board.
I would appreciate any input or advice in addition to the service manual, which is possibly the worst I've ever seen.
Thanks,
Peter Crary
N1PWC

groups.io

ya1@...
 

We already have a group there, but haven't moved over because their file/photo storage is too small. We'd likely have to leave those off the migration, and manually move the most important, perhaps creating a few "archive" groups for overflow like we already have here...


Michael Dunn

Are you considering moving this group in case Verizon cancels Yahoo groups after the takeover in the next few months? Good email groups are hard to find. But a new one might be worth investigating. I would suggest groups.io/ as a possible replacement. They are free and have full arrangements to copy the Yahoo files to your new location automatically. They intend to be a Yahoo replacement and seem to respond well to support questions. TekScopes2 has already made the move and after a few teething problems, it seems to be working fine. You can reserve your group name but you don't have to commit until you want to. Helmut has reserved a position for the LTspice group and is ready to move as soon as needed. The url is https://groups.io/ https://groups.io/

Re: Tek 465 multiplier

Fred Schumacher
 

I used the hand vacuum pump and could get. 20" vacuum.
I recommend to use a slow setting epoxy, at least a 10 minute one.
You can see the air bubbles to come out over time.
My Hv cap works fine ever since.
Good luck.
Fred


Sent from my iPad

On 2 mei 2017, at 11:15, David @DWH [TekScopes] <TekScopes@...> wrote:

The hand pump has the virtue of being very controllable. When we did
this at work to make the potting compound crystal clear, we had to be
careful how quickly the vacuum was applied because otherwise the
compound would bubble and expand out of the container.

On Tue, 2 May 2017 10:04:58 +0100, you wrote:

A vacuum pump is better - what ever you use, make sure that there is a filter in the line so that you don't get any resin in the compressor/vac pump

Robin

Sent from my iPhone

On 2 May 2017, at 09:28, David @DWH [TekScopes] <TekScopes@...> wrote:

I read somewhere about someone using a hand operated vacuum pump
normalized used for bleeding brake systems for this. The air inlet
for an air compressor will also work to draw a vacuum.

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

Re: Type 503 Oscilloscope Issues

Albert Otten
 

I still don't understand why the culprit is sought in the regulator circuit only. The phenomena were that the -100V was actually -70V while at the same time some other output voltages were near spec or even more than spec. When there is a fault in the regulator which doesn't destroy stable operation but produces -100V out of spec, then the output voltages (+250, +100, +12.6, -100) will be *all* too high or *all* too low, and the correct ratio (determined by the transformer windings) will be maintained. Hence I would first of all check that the regulator is stable. Normally I would scope-monitor the oscillator tube anode voltage but that might be dangerous here. Safer is the secondary AC output voltage between ground and the tab to D662 (or to D672 or to D682). The monitored voltage might show "motorboating". Also, when C611/C612 are bad the +500V can drop so far during parts of the mains cycle that the regulation cannot compensate this. The secondary AC voltages would periodically be too low to open the secondary rectifier diodes, leading to mains frequency related ripple in the DC outputs. A strong oscillator frequency ripple in a DC output could be the result of a too high load or a bad filter cap. The -100V is the main suspect.
Since the deviations are so very pronounced it should be not too difficult to narrow down the location of the fault I think.

Albert

Re: Tek 465 multiplier

 

The hand pump has the virtue of being very controllable. When we did
this at work to make the potting compound crystal clear, we had to be
careful how quickly the vacuum was applied because otherwise the
compound would bubble and expand out of the container.

On Tue, 2 May 2017 10:04:58 +0100, you wrote:

A vacuum pump is better - what ever you use, make sure that there is a filter in the line so that you don't get any resin in the compressor/vac pump

Robin

Sent from my iPhone

On 2 May 2017, at 09:28, David @DWH [TekScopes] <TekScopes@...> wrote:

I read somewhere about someone using a hand operated vacuum pump
normalized used for bleeding brake systems for this. The air inlet
for an air compressor will also work to draw a vacuum.

Re: Digital multimeter DM502

 

Well, I was close or at least we were heading in the right direction.
I am glad you found the problem because my next step was to do a
detailed analysis of the circuit up to that point. I know generally
how delta Vbe thermometers work but Tektronix's implementation is a
little different.

That is a good job finding that kind of problem; a couple months ago I
found a bent IC pin like that on a 7B80 timebase resulting in the
trigger level not working correctly. I suspect I bent it when
reseating the ICs years earlier.

On 01 May 2017 07:36:39 +0000, you wrote:

David,

Thank you very much for help!

It is working now! The fault was not the capasitor C263. There was no signal on pin 1 of the IC U250A. Pin was bent and had no contact. My eyesight to near objects is not in first class condition anymore!

Eino

Re: Tek 465 multiplier

 

A vacuum pump is better - what ever you use, make sure that there is a filter in the line so that you don't get any resin in the compressor/vac pump

Robin

Sent from my iPhone

On 2 May 2017, at 09:28, David @DWH [TekScopes] <TekScopes@...> wrote:

I read somewhere about someone using a hand operated vacuum pump
normalized used for bleeding brake systems for this. The air inlet
for an air compressor will also work to draw a vacuum.

On Tue, 2 May 2017 00:04:38 +0000 (UTC), you wrote:


To the Group,
Many thanks for ALL explanations concerning the multiplier construction.
The first one is running just fine,besides the 3kV capacitors, but the second one will be with a pair of 3kV in series. Acrylic resin was used. Next unit for the 468 will be with epoxy filling.
The only doubt is the vacuum proccess of getting the air bubbles off.
I Hope I can repair the 468 too!
Regards to ALL,
Sam

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

Re: Type 503 Oscilloscope Issues

ykochcal
 

A few thoughts in general come to my mind

One: removing one end of a resistor in a tek and measuring a resistor works
but can cause collateral damage.

Two: most times only one or a few parts are bad so if you can find them with
other means I would do that first.

Three: If there is a capacitor in parallel with the resistor it's best to
measure with the + lead on the capacitor + and then let the resistance rise
as the capacitor charges then take reading.

Four: (and this one has caught me before) if taking a lot of in circuit
resistance readings too fast there might be a charged capacitor which can
make a resistance look high, To be sure sometimes I clip a low ohm resistor
on to discharge everything and come back after lunch remove it and read
again.

Five: In circuit the resistance should always be lower then the value plus
tolerance (but many times things will work with +20% +50% so it's not a sure
thing it's "the" problem)

Six: Most times there is one or more resistors in parallel in some way and
that will make a lower reading so generally it's good to be lower but it
takes more effort to check for sure.

Seven: Often, If there is a more complicated resistor network (or transistor
junction), then you can connect/short some nodes in ways to get down to one
or a few resistors in parallel to simplify calculating what the reading
should be. (be sure to remove before applying power as this is only a test
to check resistors with power off).

Eight: (This happened to me) I generally clip on my resistance meter between
the resistor body and the ceramic strip. The clip leads can put enough force
on a resistor that is open to connect making it look good. So after a few
passes I clip on to the lead of the other part the resistor is connected to.
One resistor I must have measure as good a dozen times before I figured that
out and found it was open.


So if you want to learn to solder do #1, if you want to learn about
circuits, as I do (that's the fun part after all) then take some time to see
if you can figure what part is bad by looking at the circuit and estimating
what the resistance should measure in circuit . That way the oscilloscope is
useful in both states, working and when it's not working, it's teaching as
you fix it.

Good luck and keep reporting in

John

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: Tuesday, May 02, 2017 12:09 AM
To: TekScopes@...
Subject: [TekScopes] Re: Type 503 Oscilloscope Issues

I replied before I saw Dave's last message, but in checking R624 again
(holding the probes while the capacitor charged up), the final resistance
measured was 33.2 ohm, which is higher than the rated 22 ohm. I also caught
my mistake in reading the resistor codes when comparing to the manual, and
the previous update I sent out was in reference to the correct values (as
displayed on the image).

As for the transformer, I will take a look at that later today or tomorrow
and see what happens once wired in place.


- Evan






------------------------------------
Posted by: enchanter464@...
------------------------------------


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

Yahoo Groups Links

Re: Tek 465 multiplier

 

I read somewhere about someone using a hand operated vacuum pump
normalized used for bleeding brake systems for this. The air inlet
for an air compressor will also work to draw a vacuum.

On Tue, 2 May 2017 00:04:38 +0000 (UTC), you wrote:


To the Group,
Many thanks for ALL explanations concerning the multiplier construction.
The first one is running just fine,besides the 3kV capacitors, but the second one will be with a pair of 3kV in series. Acrylic resin was used. Next unit for the 468 will be with epoxy filling.
The only doubt is the vacuum proccess of getting the air bubbles off.
I Hope I can repair the 468 too!
Regards to ALL,
Sam

Re: Type 503 Oscilloscope Issues

Dave Casey
 

I would recommend replacing R624 and R632 toward your goal of correcting
the supply voltages.

Dave Casey

On Tue, May 2, 2017 at 2:08 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



I replied before I saw Dave's last message, but in checking R624 again
(holding the probes while the capacitor charged up), the final resistance
measured was 33.2 ohm, which is higher than the rated 22 ohm. I also caught
my mistake in reading the resistor codes when comparing to the manual, and
the previous update I sent out was in reference to the correct values (as
displayed on the image).

As for the transformer, I will take a look at that later today or tomorrow
and see what happens once wired in place.


- Evan




Re: Type 503 Oscilloscope Issues

Evan
 

I replied before I saw Dave's last message, but in checking R624 again (holding the probes while the capacitor charged up), the final resistance measured was 33.2 ohm, which is higher than the rated 22 ohm. I also caught my mistake in reading the resistor codes when comparing to the manual, and the previous update I sent out was in reference to the correct values (as displayed on the image).

As for the transformer, I will take a look at that later today or tomorrow and see what happens once wired in place.


- Evan

Re: Type 503 Oscilloscope Issues

Dave Casey
 

All of the resistances that you have cited as low or very low need to be
measured out of circuit to get an accurate reading. This type of resistor
tends to drift high, not low. You can get a sense of whether or not
anything is drastically wrong here by measuring voltages as marked in the
schematic. Because you do not have the correct supply voltages, you cannot
expect the same bias voltages as what's marked, however everything should
be proportionally correct within an order of magnitude (i.e. V634 pin 3
should be approximately 60% of whatever the +100V bus is measuring). You
can also check the resistors one at a time by desoldering one of the leads
from the terminal strip.

R632 is just barely out of tolerance, and you may replace it if you so
desire.

R692 does sound a bit high, but I believe you previously reported a
measurement for R692 (before you removed and replaced V692) that was within
reason. It's unlikely that R692 has suddenly gone high. Perhaps you're not
making good contact for your measurement, or you have a less than perfect
connection with your soldering job? Regardless, if V692 is glowing gently
and you get a trace on the CRT, I wouldn't worry too much about R692.

You should know where R641 is as you've adjusted it before with no effect,
have you not?

As I stated earlier, you should be able to measure R624, so if you are
unable to get a measurement there, you need to determine why.


Dave Casey


On Tue, May 2, 2017 at 1:22 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



Thanks Dave for that correction on R692. I had mistyped the color code in
my resistor calculator, and it did not click in my mind that the units from
my multimeter did not match (just assumed it to be of the same magnitude).

As for matching the resistors to the manual's diagram, I updated the
figure with the corresponding part labels (again, can view at
https://goo.gl/photos/JUFwEfmnyFAcYtp6A https://goo.gl/photos/
JUFwEfmnyFAcYtp6A). They should all be labelled correctly, although some
wires are difficult to trace and the resistors could be mixed up.


To simplify things, I have each resistor listed below as well:
- R611 = 151.2 k (good)
- R612 = 140.5 k (good)
- R621 = 94.7 k (good)
- R623 = 4.65 k (good)
- R624 = ? (could not get a measurement)
- R626 = ? (could not locate)
- R628 = 508 ohm (good)
- R630 = 537 k (low)
- R631 = 752 k (very low)
- R632 = 116 ohm (high)
- R634 = 20.5 k (low)
- R635 = 22.3 k (very low)
- R637 = 400 k (low)
- R640 = ? (could not locate)
- R641 = ? (could not locate)
- R642 = ? (could not locate)
- R644 = 465 k (good)
- R646 = 15.3 k (good)
- R659 = 77.9 k (low)
- R692 = 8.9 ohm (very high)




- Evan

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



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

Re: Type 503 Oscilloscope Issues

Evan
 

Thanks Dave for that correction on R692. I had mistyped the color code in my resistor calculator, and it did not click in my mind that the units from my multimeter did not match (just assumed it to be of the same magnitude).

As for matching the resistors to the manual's diagram, I updated the figure with the corresponding part labels (again, can view at https://goo.gl/photos/JUFwEfmnyFAcYtp6A https://goo.gl/photos/JUFwEfmnyFAcYtp6A). They should all be labelled correctly, although some wires are difficult to trace and the resistors could be mixed up.


To simplify things, I have each resistor listed below as well:
- R611 = 151.2 k (good)
- R612 = 140.5 k (good)
- R621 = 94.7 k (good)
- R623 = 4.65 k (good)
- R624 = ? (could not get a measurement)
- R626 = ? (could not locate)
- R628 = 508 ohm (good)
- R630 = 537 k (low)
- R631 = 752 k (very low)
- R632 = 116 ohm (high)
- R634 = 20.5 k (low)
- R635 = 22.3 k (very low)
- R637 = 400 k (low)
- R640 = ? (could not locate)
- R641 = ? (could not locate)
- R642 = ? (could not locate)
- R644 = 465 k (good)
- R646 = 15.3 k (good)
- R659 = 77.9 k (low)
- R692 = 8.9 ohm (very high)




- Evan

Re: Type 503 Oscilloscope Issues

Dave Casey
 

Evan -

I've sent the schematic to you in a direct e-mail where the attachment
shouldn't get stripped. Let me know if you continue to have issues, and I
can put it on imgur or something.

Before you go trying to solve problems you don't have, I would wire in the
new transformer and see if the scope works again. It probably will. The
issue will just be that the power supply voltages are not to spec. It may
have always had this problem and you weren't aware of it because the scope
worked well enough for your purposes.

It's very likely that at least some of the resistors are now out of
tolerance, but you will have a hard time determining that by measuring them
in circuit as you've done. You are correct that the measurements are skewed
by the other components. One of your EE friends who has done the basic
circuit theory coursework can help you determine approximate measurement
values by performing nodal analyses using the schematic. Even though they
are not familiar with tubes, this being a tube scope doesn't complicate
things very much for these types of measurements. When everything is
powered off and you're just checking resistances with a DMM, it's basically
as though the tubes aren't even there.

The resistor you couldn't measure (???), which is supposed to be 22 ohms,
is R624. Your difficulty in measurement may be due to C624 (the little
yellow electrolytic on the back of V620). You should be able to read get a
solid reading on that resistor if you keep your leads connected long enough
for C624 to charge. If you can never get a stable reading, C624 may be
faulty. The presence or absence of V620 should not affect this measurement
either. If the measurement changes when the tube is removed, then V620 has
developed some internal shorts and needs to be replaced.

You've mis-read the values of several resistors. All those you've marked as
48 are actually supposed to be 47. Violet is 7, black is 0. Due to math and
the way resistors are made, 47 is a common value whereas 48 is not. Google
"standard resistor values" and have a look at the E12 series to get a sense
of the common significant figures you can expect to encounter in this
scope. (or just see here:
http://www.rfcafe.com/references/electrical/resistor-values.htm ).

I will look over your measured values as I have time, but I would recommend
you take a close look at R624 in the meantime.


Dave Casey


On Mon, May 1, 2017 at 11:21 PM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



It has been a while since last posting, but I have only gotten time
recently to work on the scope (in the midst of final exams).

Taking Dave's advice, I went ahead and measured the resistance of the
resistors surrounding V620 and V634 (basically everything on the ceramic
strips). I have a photo of my measurements here: https://goo.gl/photos/
JUFwEfmnyFAcYtp6A https://goo.gl/photos/JUFwEfmnyFAcYtp6A


I was unable to measure the resistor across V620, which is why there are
"???" for that value. Those values reported in red were the ones outside of
the tolerance range. Suffice to say, the majority of the resistors gave
values that were outside of their range. However, I am not sure if this is
due to how some are soldered together, which could affect the values (for
example, the resistor at V692 giving a resistance value of just the tube
itself, since its expected value is relatively small). In addition, only
one resistor (a 100 ohm) had values higher than its range, while the others
were all below their tolerance limit.


Before looking at getting a replacement tube for V620, would it be best to
replace these resistors? Or is there a better way I can test resistance to
confirm that the values I measured are accurate?


Also, a side note for Dave, but the schematic for wiring the 6.3 VAC
transformer did not get added to your posting. Would you be able to share
the image as a link (since the forums don't support attaching photos)?


- Evan


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



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

Re: Type 503 Oscilloscope Issues

Dave Casey
 

The lower right one is R692. Evan has listed the marked value, the allowed
range factoring in for tolerance, and the measured value in that order for
each resistor he's measured. However, he's mis-read R692 as 0.43 ohms
instead of 4.3 ohms, and he's accidentally marked it as 0.42 ohms even
though his tolerance range is correct for the incorrect value he's read off
the bands.

Dave Casey

On Mon, May 1, 2017 at 11:55 PM, 'Tom Miller' tmiller11147@...
[TekScopes] <TekScopes@...> wrote:



What is the one in the lower right 0.42 ohms? That is way out of range,
maybe open?

----- Original Message -----
From: enchanter464@... [TekScopes]
To: TekScopes@...
Sent: Tuesday, May 02, 2017 12:21 AM
Subject: [TekScopes] Re: Type 503 Oscilloscope Issues

It has been a while since last posting, but I have only gotten time
recently to work on the scope (in the midst of final exams).

Taking Dave's advice, I went ahead and measured the resistance of the
resistors surrounding V620 and V634 (basically everything on the ceramic
strips). I have a photo of my measurements here: https://goo.gl/photos/
JUFwEfmnyFAcYtp6A https://goo.gl/photos/JUFwEfmnyFAcYtp6A

I was unable to measure the resistor across V620, which is why there are
"???" for that value. Those values reported in red were the ones outside of
the tolerance range. Suffice to say, the majority of the resistors gave
values that were outside of their range. However, I am not sure if this is
due to how some are soldered together, which could affect the values (for
example, the resistor at V692 giving a resistance value of just the tube
itself, since its expected value is relatively small). In addition, only
one resistor (a 100 ohm) had values higher than its range, while the others
were all below their tolerance limit.

Before looking at getting a replacement tube for V620, would it be best to
replace these resistors? Or is there a better way I can test resistance to
confirm that the values I measured are accurate?

Also, a side note for Dave, but the schematic for wiring the 6.3 VAC
transformer did not get added to your posting. Would you be able to share
the image as a link (since the forums don't support attaching photos)?

- Evan

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

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



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