Date   

Re: Tek 2247A [SN B029000] Recap and diode part list ?

 

And leave space between the printed circuit board and the replacements
so they can cool better.

On Mon, 14 Mar 2016 04:27:04 -0500, you wrote:

It is the four 5.1 ohm resistors that are running hot and not the
diodes. The existing resistors are 0.2 watts; replacing them with
carbon film 5.1 ohm 1/2 watt resistors would help if you are worried
about it.

On Mon, 14 Mar 2016 09:12:50 +0000 (UTC), you wrote:

Hi David,
Just uploaded picture of burn mark at folder
2247A-PSUhttps://groups.yahoo.com/neo/groups/TekScopes/files/2247A-PSU/


Re: Tek 2247A [SN B029000] Recap and diode part list ?

 

It is the four 5.1 ohm resistors that are running hot and not the
diodes. The existing resistors are 0.2 watts; replacing them with
carbon film 5.1 ohm 1/2 watt resistors would help if you are worried
about it.

On Mon, 14 Mar 2016 09:12:50 +0000 (UTC), you wrote:

Hi David,
Just uploaded picture of burn mark at folder
2247A-PSUhttps://groups.yahoo.com/neo/groups/TekScopes/files/2247A-PSU/

From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Monday, 14 March 2016, 17:07
Subject: Re: [TekScopes] Tek 2247A [SN B029000] Recap and diode part list ?

On Mon, 14 Mar 2016 04:08:37 +0000 (UTC), you wrote:

Hi David,

Thanks for your great advice.
looking at the colour in this area make me really worry.
Plan to do following:-
1. Replace all those big cap with 3-lead, it is so massive block the FAN air flow to reach CR2227 and CR2228 directly.  Due to this overheat and burn spot happen perhaps?
I doubt it. Those diodes should not be running hot with or without
air flow. They only see the base current of the transistors at a 50%
duty cycle and that should be significantly less than their 1 amp
rating.

2. Film cap show hair line crack, need to replace, no exception.

3. Replace CR2227 and CR2228 with MUR160G and solder it with 1cm above the PCB service rather than touching the board [more expose to FAN air flow for cooler operation].
CR2227 and CR2228 are Tektronix part number 152-0400-00 which is a
400V 1A 200ns 1N4936 and one of the most common fast recovery
rectifiers. An MUR160G is faster and higher voltage and will work
fine as a replacement. The circuit itself does not require a high
voltage part; a 100 volt 1N4934 or 50 volt MUR105 would also work.


Re: Tek 2247A [SN B029000] Recap and diode part list ?

Darren Ting
 

Hi David,
Just uploaded picture of burn mark at folder
2247A-PSUhttps://groups.yahoo.com/neo/groups/TekScopes/files/2247A-PSU/


From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Monday, 14 March 2016, 17:07
Subject: Re: [TekScopes] Tek 2247A [SN B029000] Recap and diode part list ?

 

On Mon, 14 Mar 2016 04:08:37 +0000 (UTC), you wrote:

Hi David,

Thanks for your great advice.
looking at the colour in this area make me really worry.
Plan to do following:-
1. Replace all those big cap with 3-lead, it is so massive block the FAN air flow to reach CR2227 and CR2228 directly.  Due to this overheat and burn spot happen perhaps?
I doubt it. Those diodes should not be running hot with or without
air flow. They only see the base current of the transistors at a 50%
duty cycle and that should be significantly less than their 1 amp
rating.

2. Film cap show hair line crack, need to replace, no exception.

3. Replace CR2227 and CR2228 with MUR160G and solder it with 1cm above the PCB service rather than touching the board [more expose to FAN air flow for cooler operation].
CR2227 and CR2228 are Tektronix part number 152-0400-00 which is a
400V 1A 200ns 1N4936 and one of the most common fast recovery
rectifiers. An MUR160G is faster and higher voltage and will work
fine as a replacement. The circuit itself does not require a high
voltage part; a 100 volt 1N4934 or 50 volt MUR105 would also work.
#yiv8035101823 #yiv8035101823 -- #yiv8035101823ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv8035101823 #yiv8035101823ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv8035101823 #yiv8035101823ygrp-mkp #yiv8035101823hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv8035101823 #yiv8035101823ygrp-mkp #yiv8035101823ads {margin-bottom:10px;}#yiv8035101823 #yiv8035101823ygrp-mkp .yiv8035101823ad {padding:0 0;}#yiv8035101823 #yiv8035101823ygrp-mkp .yiv8035101823ad p {margin:0;}#yiv8035101823 #yiv8035101823ygrp-mkp .yiv8035101823ad a {color:#0000ff;text-decoration:none;}#yiv8035101823 #yiv8035101823ygrp-sponsor #yiv8035101823ygrp-lc {font-family:Arial;}#yiv8035101823 #yiv8035101823ygrp-sponsor #yiv8035101823ygrp-lc #yiv8035101823hd {margin:10px 0px;font-weight:700;font-size:78%;line-height:122%;}#yiv8035101823 #yiv8035101823ygrp-sponsor #yiv8035101823ygrp-lc .yiv8035101823ad {margin-bottom:10px;padding:0 0;}#yiv8035101823 #yiv8035101823actions {font-family:Verdana;font-size:11px;padding:10px 0;}#yiv8035101823 #yiv8035101823activity {background-color:#e0ecee;float:left;font-family:Verdana;font-size:10px;padding:10px;}#yiv8035101823 #yiv8035101823activity span {font-weight:700;}#yiv8035101823 #yiv8035101823activity span:first-child {text-transform:uppercase;}#yiv8035101823 #yiv8035101823activity span a {color:#5085b6;text-decoration:none;}#yiv8035101823 #yiv8035101823activity span span {color:#ff7900;}#yiv8035101823 #yiv8035101823activity span .yiv8035101823underline {text-decoration:underline;}#yiv8035101823 .yiv8035101823attach {clear:both;display:table;font-family:Arial;font-size:12px;padding:10px 0;width:400px;}#yiv8035101823 .yiv8035101823attach div a {text-decoration:none;}#yiv8035101823 .yiv8035101823attach img {border:none;padding-right:5px;}#yiv8035101823 .yiv8035101823attach label {display:block;margin-bottom:5px;}#yiv8035101823 .yiv8035101823attach label a {text-decoration:none;}#yiv8035101823 blockquote {margin:0 0 0 4px;}#yiv8035101823 .yiv8035101823bold {font-family:Arial;font-size:13px;font-weight:700;}#yiv8035101823 .yiv8035101823bold a {text-decoration:none;}#yiv8035101823 dd.yiv8035101823last p a {font-family:Verdana;font-weight:700;}#yiv8035101823 dd.yiv8035101823last p span {margin-right:10px;font-family:Verdana;font-weight:700;}#yiv8035101823 dd.yiv8035101823last p span.yiv8035101823yshortcuts {margin-right:0;}#yiv8035101823 div.yiv8035101823attach-table div div a {text-decoration:none;}#yiv8035101823 div.yiv8035101823attach-table {width:400px;}#yiv8035101823 div.yiv8035101823file-title a, #yiv8035101823 div.yiv8035101823file-title a:active, #yiv8035101823 div.yiv8035101823file-title a:hover, #yiv8035101823 div.yiv8035101823file-title a:visited {text-decoration:none;}#yiv8035101823 div.yiv8035101823photo-title a, #yiv8035101823 div.yiv8035101823photo-title a:active, #yiv8035101823 div.yiv8035101823photo-title a:hover, #yiv8035101823 div.yiv8035101823photo-title a:visited {text-decoration:none;}#yiv8035101823 div#yiv8035101823ygrp-mlmsg #yiv8035101823ygrp-msg p a span.yiv8035101823yshortcuts {font-family:Verdana;font-size:10px;font-weight:normal;}#yiv8035101823 .yiv8035101823green {color:#628c2a;}#yiv8035101823 .yiv8035101823MsoNormal {margin:0 0 0 0;}#yiv8035101823 o {font-size:0;}#yiv8035101823 #yiv8035101823photos div {float:left;width:72px;}#yiv8035101823 #yiv8035101823photos div div {border:1px solid #666666;height:62px;overflow:hidden;width:62px;}#yiv8035101823 #yiv8035101823photos div label {color:#666666;font-size:10px;overflow:hidden;text-align:center;white-space:nowrap;width:64px;}#yiv8035101823 #yiv8035101823reco-category {font-size:77%;}#yiv8035101823 #yiv8035101823reco-desc {font-size:77%;}#yiv8035101823 .yiv8035101823replbq {margin:4px;}#yiv8035101823 #yiv8035101823ygrp-actbar div a:first-child {margin-right:2px;padding-right:5px;}#yiv8035101823 #yiv8035101823ygrp-mlmsg {font-size:13px;font-family:Arial, helvetica, clean, sans-serif;}#yiv8035101823 #yiv8035101823ygrp-mlmsg table {font-size:inherit;font:100%;}#yiv8035101823 #yiv8035101823ygrp-mlmsg select, #yiv8035101823 input, #yiv8035101823 textarea {font:99% Arial, Helvetica, clean, sans-serif;}#yiv8035101823 #yiv8035101823ygrp-mlmsg pre, #yiv8035101823 code {font:115% monospace;}#yiv8035101823 #yiv8035101823ygrp-mlmsg * {line-height:1.22em;}#yiv8035101823 #yiv8035101823ygrp-mlmsg #yiv8035101823logo {padding-bottom:10px;}#yiv8035101823 #yiv8035101823ygrp-msg p a {font-family:Verdana;}#yiv8035101823 #yiv8035101823ygrp-msg p#yiv8035101823attach-count span {color:#1E66AE;font-weight:700;}#yiv8035101823 #yiv8035101823ygrp-reco #yiv8035101823reco-head {color:#ff7900;font-weight:700;}#yiv8035101823 #yiv8035101823ygrp-reco {margin-bottom:20px;padding:0px;}#yiv8035101823 #yiv8035101823ygrp-sponsor #yiv8035101823ov li a {font-size:130%;text-decoration:none;}#yiv8035101823 #yiv8035101823ygrp-sponsor #yiv8035101823ov li {font-size:77%;list-style-type:square;padding:6px 0;}#yiv8035101823 #yiv8035101823ygrp-sponsor #yiv8035101823ov ul {margin:0;padding:0 0 0 8px;}#yiv8035101823 #yiv8035101823ygrp-text {font-family:Georgia;}#yiv8035101823 #yiv8035101823ygrp-text p {margin:0 0 1em 0;}#yiv8035101823 #yiv8035101823ygrp-text tt {font-size:120%;}#yiv8035101823 #yiv8035101823ygrp-vital ul li:last-child {border-right:none !important;}#yiv8035101823



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


New file uploaded to TekScopes

TekScopes@...
 

Hello,


This email message is a notification to let you know that
a file has been uploaded to the Files area of the TekScopes
group.


File : /2247A-PSU/A18CR2227_CR2228_PCB_BurnMark-Front.jpg
Uploaded by : darren_ting_hc <darren_ting_hc@...>
Description : PSU Working fine but having those BURN mark


You can access this file at the URL:
https://groups.yahoo.com/neo/groups/TekScopes/files/2247A-PSU/A18CR2227_CR2228_PCB_BurnMark-Front.jpg


To learn more about file sharing for your group, please visit:
https://help.yahoo.com/kb/index?page=content&y=PROD_GRPS&locale=en_US&id=SLN15398


Regards,


darren_ting_hc <darren_ting_hc@...>


New file uploaded to TekScopes

TekScopes@...
 

Hello,


This email message is a notification to let you know that
a file has been uploaded to the Files area of the TekScopes
group.


File : /2247A-PSU/A18CR2227_CR2228_PCB_BurnMark-Back.jpg
Uploaded by : darren_ting_hc <darren_ting_hc@...>
Description : PSU Working fine but having those BURN mark


You can access this file at the URL:
https://groups.yahoo.com/neo/groups/TekScopes/files/2247A-PSU/A18CR2227_CR2228_PCB_BurnMark-Back.jpg


To learn more about file sharing for your group, please visit:
https://help.yahoo.com/kb/index?page=content&y=PROD_GRPS&locale=en_US&id=SLN15398


Regards,


darren_ting_hc <darren_ting_hc@...>


Re: Tek 2247A [SN B029000] Recap and diode part list ?

 

On Mon, 14 Mar 2016 04:08:37 +0000 (UTC), you wrote:

Hi David,

Thanks for your great advice.
looking at the colour in this area make me really worry.
Plan to do following:-
1. Replace all those big cap with 3-lead, it is so massive block the FAN air flow to reach CR2227 and CR2228 directly.  Due to this overheat and burn spot happen perhaps?
I doubt it. Those diodes should not be running hot with or without
air flow. They only see the base current of the transistors at a 50%
duty cycle and that should be significantly less than their 1 amp
rating.

2. Film cap show hair line crack, need to replace, no exception.

3. Replace CR2227 and CR2228 with MUR160G and solder it with 1cm above the PCB service rather than touching the board [more expose to FAN air flow for cooler operation].
CR2227 and CR2228 are Tektronix part number 152-0400-00 which is a
400V 1A 200ns 1N4936 and one of the most common fast recovery
rectifiers. An MUR160G is faster and higher voltage and will work
fine as a replacement. The circuit itself does not require a high
voltage part; a 100 volt 1N4934 or 50 volt MUR105 would also work.


Re: 7854 RAM card upgrade only - any interest?

 

On 13 Mar 2016 21:59:25 -0700, you wrote:

In my manual (pre B100000), the A3 layout is Figure 7-25 on the back of diagram 17. C430 is identified just above the middle of P108 (between P108 and P430, which is a row of pins connecting through to the keybutton board).
My pre-B100000 manual shows no C430 location but I checked my
post-B100000 manual and it shows what you describe. I prefer to use
the scan of the older manual because the scan of the newer manual is
poorer quality; the component numbers in figure 7-25 are visible on it
but the outlines are only hinted.

However, on my A3 board there is no capacitor at that location! I therefore identified all of the caps shown on the layout drawing and the wiring diagram, and compared with the actual board. The board seems to match the layout drawing in all respects but one:

There is one unaccounted for cap. It is midway between P430 and U520, just about where the black hexagon identifying waveform test point 3 is located on the A3 layout drawing figure 7-25 with drawing id 2874-722A.

If we can establish through testing that C430 should never have been there, we could just cut pin 5 of P108, which might even be possible without removing the board from the scope - but we have to be sure first. Harder to reach, but less destructive would be to cut one lead of the mystery capacitor which is almost certainly C430.

Removing A3 from the scope looks like a huge disassembly job at first examination.
I am sure I can establish that C430 was added by mistake but I do not
think it matters for three reasons:

1. C430 is hard to get to and there may be undocumented variations.

2. C430 apparently caused no reliability problems with U310 (schematic
27), U15 (schematic 36), and U220 (schematic 19) despite the drivers
fighting on lines K0 and K7 and even oscillating. I wonder if there
were mysterious failures of these ICs.

3. The issue can be resolved by installing low valued resistors to
limit the current in series with the outputs of U15F (or the collector
of the transistor inverter I suggest as a replacement) and U220F where
the resistor can replace the jumper inside the external calculator
keyboard.

I disconnected P108 and tried to measure the capacitance between A3 pin 5 and ground - but my capacitance bridge insisted on oscillating unstably. It's never done that before. Maybe my test leads were a bit too long.

Cliff
I found another potentially useful feature to add to a combined memory
board for practically free. If 27256s are used to replace the 27128s,
then the extra half of the ROM space can be used to hold the firmware
from the Diagnostic Memory Board (if the firmware will fit in 32KBytes
starting at 0000h) with a jumper to the extra address bit to select
which firmware image is active.

Of course we do not have the firmware to even one of the Diagnostic
Memory Boards and apparently the firmware is specific to different
versions of the 7854.


Re: Tek 2247A [SN B029000] Recap and diode part list ?

Malcolm Hunter
 

On 14 March 2016 at 01:50, TING HENG CHING darren_ting_hc@...
[TekScopes] <TekScopes@...> wrote:

Any advice why this area get so hot till cause a scorch mark on PCB?

I have the picture but not sure how to attached it in here
​You can upload files here:
https://groups.yahoo.com/neo/groups/TekScopes/files

Malcolm​


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


Re: OT 10Mhz references

Craig Sawyers <c.sawyers@...>
 

I once read a fascinating article on what is done to keep the Cesium Clocks on the GPS satellites
accurate. If I remember correctly there are five different relativistic effects that have to be
compensated for. Frame dragging is one of the most interesting. Another effect comes from the
satellites continuously falling (accelerating) into the earth but missing as they whip around in
space. I
think another one is they feel the effects of micro gravity, etc.
Dennis Tillman W7PF
I'd forgotten about frame dragging. The largest effect by far is the special relativity effect as a
result of satellite motion with respect to the receiver. But absolutely all effects, calculable or
not have to be corrected for. The amazing thing is that only a tiny number of folks like us are
impressed with all that. Everyone else uses their satnav every day without the blindest idea how
difficult the technology is; atomic clocks in orbit corrected for relativistic effects - "In 400
metres turn left towards London" is all they see or hear.


Re: Hullo Intro, Thank You

Michael
 

Menahem,

Thanks for your feedback.

I understand that I may not have selected the optimal components. The BOM is
all that I had during initial parts selection and since I don't know the
mind of Tektronix's engineers, I went with the same type of resistor but with
a larger wattage rating and improved voltage rating. During my initial rebuild
I didn't want to stray too far from original parts with some obvious
exceptions such as improved ratings for voltage or wattage. Especially since
this is my only scope and my first hardware rebuild.

The resistor selection should not be any worse than the factory parts and
should be better. I went with 1W resistors because my initial choice of 3W
resistors was too large physically. Since the goal was to increase wattage to
avoid the original problems, doubling the wattage to 1W should be sufficient
to prevent a repeat of the original problem. The new 1W resistors are the same
size as the original resistors.

You have a good point about metal film, but they are not causing any obvious
problems. After repair, all of my supply voltages are spot on, and the ripple
is also well within specification.

As far as the C1021 and C1022 capacitors are concerned, I prefer to replace
with the same type of parts. No, I couldn't find the higher temperature
axials. Yes, I could hack in a radial, but I didn't want to do that. Hacking
the wire leads was bad enough. Those were the only 85C parts and, again, were
no worse than the originals with increased capacitance. Realistically, the
scope is not going to operating anywhere near the boiling point of water! The
temperature rating largely is needed to extend the capacitor's lifespan. Since
these are isolated in their mounting, above the board, there isn't likely to
be a problem from using the 85C parts.

At this point, I have probably had the scope open a couple of dozen times. I
have had every board out at least once for recapping. I have had the processor
board out several times and the power boards more than a half-dozen times. I
have gained a lot of experience working with the scope, and popping out most
of the boards is largely routine now. I also disassembled the front so that it
could be cleaned. I have completely cleaned the outside of the scope removing
all kinds of gunk. The inside was very clean except near the exploded RIFA
capacitor. I cleaned that as well.

Once I had the scope completely repaired, except for recalibration, I have
gone back and made more changes. In particular, I changed out most of the
capacitors on the A2A1 board to improve ripple. The reference 10v is fed into
the other voltage regulators, and all of the noise on it is faithfully copied
into the other voltages. Since the 10v output was unfiltered, I piggybacked a
UHE1E331MPD 330uF filter capacitor across VR1293. I also replaced the 47uF and
100uF capacitors with UHE1E331MPD 330uF capacitors and the 10uF 100V
capacitors with UHE2A121MHD6 120uF. Surge current is not an issue because the
input circuit limits initial current flow with the thermal resistors (one of
which I replaced and intend to replace the other once I get it). I also
replaced the bridge because it was bad and as a precaution replaced the surge
suppressors.

The result is drastically reduced ripple on all voltages. Most of them now
have maximum ripple of around 1mV to 2mV with no observable power line related
ripple at all. The one voltage with higher ripple has had almost all of the
non-power line related noise removed and the power line ripple reduced. And
well below specification. Even the unregulated voltages are cleaner.

I replaced the fan and feed through capacitor as part of the repair. I also
replaced the fan with a lower RPM, lower power, quieter fan with higher air
flow. While I was at it, I added an extra 0.1uF ceramic capacitor to help
filter fan motor noise across the fan's ground and power wires. I measured the
temperature of the U800 IC and found that it was barely warm, certainly not
hot. So, I elected to NOT add a heat sink to it.

I have added Option 1E and modified that by adding a 50 ohm resistor for
proper termination which Tektronix (intentionally) omitted. I added Option 11
(not originally available for the BCT). I had to drill two holes, get some
Lemo connectors and build the cables, but I now have two probe power sockets.
The hardest part was placement, because the back is very crowded. There are
pictures on eevBlog.

I have also replaced the original 10Mhz crystal with 100ppm aging with a 10ppm
crystal (changing the 33pF / 82pF capacitors to 33pF / 33pF - both so that
they are identical). This does not affect the time base, but when the scope is
recalibrated, the calibration constants should be closer to the center of
their range and the scope will drift out of calibration at a slower rate.

I also plan on upgrading the firmware from version -04 with -10 (I have the
dump of the -10 firmware and the EEROM needed). I wanted to update to the -11
firmware, but have been unable to find it anywhere (it actually adds some very
minor features). If you -11 firmware, I would definitely appreciate a copy!

Updating the firmware will require calibration. I also plan on removing the
RAM and replacing it with FRAM. Again, I have those parts ready to go. Both of
these will need to be done just before calibration and need a reader / writer
which I don't have. I have a friend with the necessary calibration equipment
(and a reader / writer) who will assist me with these changes and the
calibration.

As far as not opening the scope up again in my lifetime - I expect to live for
many centuries. Aging is nearly defeated and I plan on sticking around for a
long, long time. I have far too many projects to quit any time this millennium!

And, of course, in merely another 10 or 20 years, it will probably be time to
recap again!


Mike


Mike

I'm going to disagree with your choice of some of those components.


Firstly, the PR01 resistors. They are rated at ONE watt - yes, I know that, but they are METAL-FILM.
Metal-film resistors are NOT capable of handling pulses to the same
degree as Carbon or Ceramic resistors, and they also have a much steeper derating curve - not good.


Not only that, but Metal-Film are also INDUCTIVE. Which can cause
oscillation at certain frequencies in this circuit.


No matter what the original BoM specified, we need to take a good hard
look at why certain components are prone to failure, and that situation
simply points to a generally poor choice in the original BoM.


So selecting again, according to the original BoM, is NOT the smartest idea.


Therefore those PR01's are a BAD choice in this circuit. (They are very
high quality resistors in their own right, but NOT suitable HERE).


Much better to use Ceramic 3W resistors - Panasonic or Yageo offer a wide selection.


The big Sprague axials - why do you select a 85C replacement? This whole
environment gets very warm - we know that. Once you're doing the work, why
not use better quality components? OK, so you can't find an axial
replacement? So what! Use a better-quality 105C radial cap (Nichicon HE, PW,
etc), and run 2 wires up to the caps leads from the PCB.


The objective of this work MUST be - I will use the best quality parts,
so that I will NOT have to open up my scope again in my lifetime!


Menahem Yachad
Israel





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





--
Best regards,
2465bct mailto:2465bct@...


Re: OT 10Mhz references

Torch Fireman
 

Dennis,-

In 2007 the DST dates were changed to run from 2nd Sunday of March to 1st Sunday of November. My watch follows the old rules and changes itself on the first Sunday in April and the last Sunday of October if left to it's own devices. You may well be correct that the WWVB transmission includes DST information, but if so, my watch wants no truck with such new-fangled ideas.

On 14/03/2016 1:18 AM, 'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes] wrote:

I don't understand why your watch doesn't
automatically update to DST since I'm pretty sure Daylight Savings Time and
Standard Time information is part of the WWVB transmission. The only thing
you have to do when you get one of these clocks is choose your time zone
since WWVB doesn't have any way to know where you are (east or west) in the
US.


Re: Hullo Intro, Thank You

 

Mike

I'm going to disagree with your choice of some of those components.


Firstly, the PR01 resistors. They are rated at ONE watt - yes, I know that, but they are METAL-FILM.
Metal-film resistors are NOT capable of handling pulses to the same degree as Carbon or Ceramic resistors, and they also have a much steeper derating curve - not good.


Not only that, but Metal-Film are also INDUCTIVE. Which can cause oscillation at certain frequencies in this circuit.


No matter what the original BoM specified, we need to take a good hard look at why certain components are prone to failure, and that situation simply points to a generally poor choice in the original BoM.


So selecting again, according to the original BoM, is NOT the smartest idea.


Therefore those PR01's are a BAD choice in this circuit. (They are very high quality resistors in their own right, but NOT suitable HERE).


Much better to use Ceramic 3W resistors - Panasonic or Yageo offer a wide selection.


The big Sprague axials - why do you select a 85C replacement? This whole environment gets very warm - we know that. Once you're doing the work, why not use better quality components? OK, so you can't find an axial replacement? So what! Use a better-quality 105C radial cap (Nichicon HE, PW, etc), and run 2 wires up to the caps leads from the PCB.


The objective of this work MUST be - I will use the best quality parts, so that I will NOT have to open up my scope again in my lifetime!


Menahem Yachad
Israel


Re: OT 10Mhz references

 

Hi Greg,
I heard something like that a few years ago. But at that time Cesium
Fountains were not much more accurate than Rb standards which made me wonder
if Tom would be interested in something that was LESS accurate even if it
was portable.

John Miles might know what Tom is up to now.

Dennis Tillman W7PF

-----Original Message-----
Sent: Sunday, March 13, 2016 9:59 AM
Subject: Re: [TekScopes] Re: OT 10Mhz references

I'm sure that somewhere in Tom Van Baak's basement is an ongoing project to
construct a Cesium fountain atomic clock. Then the HP Cesium units may come
up for sale.

Greg
------------------------------------
Posted by: big_sky_explorer@...
------------------------------------


Re: OT 10Mhz references

 

Hi Dwayne,
I once read a fascinating article on what is done to keep the Cesium Clocks
on the GPS satellites accurate. If I remember correctly there are five
different relativistic effects that have to be compensated for. Frame
dragging is one of the most interesting. Another effect comes from the
satellites continuously falling (accelerating) into the earth but missing as
they whip around in space. I think another one is they feel the effects of
micro gravity, etc.

All of these relativistic effects have to be taken into account when
updating the satellites or the entire system wouldn't work at all.

At any moment up to 12 of the 24 satellites are at or above the horizon
wherever you are on earth. But the atmosphere affects the strength and
accuracy of the signals. So a GPS receiver, although it may be capable of
receiving 12 satellite's signals will select the best ones to use to perform
its calculations. The best ones are the ones highest in the sky overhead.
You can use so-called "choker" GPS antennas to eliminate signals from
satellites at low azimuth angles to improve the location accuracy and time
accuracy if that is important to your application.

A GPSDO is typically receiving continuous time information from 5 or 6
satellites (in space) at a time and performing calculations on the data
being received. The disciplined crystal oscillator inside the GPSDO (on the
earth) is continuously being adjusted to be within ~10 x ^-13 Sec. If there
were a discrepancy in how fast the clock was running due to the signal
reaching you in the gravity well of the earth the system wouldn't work at
all and your Lat. / Long. / Altitude coordinates would only be correct at
one specific point on earth since magma chambers, ore deposits, etc. create
gravity anomalies everywhere.

My understanding of the so-called atomic clocks sold in stores (and your
watch sounds like one of them) is that they work on the WWVB 60KHz
transmissions from Colorado Springs. Those transmissions were modified 5-8
years ago (which screwed up all the VLF receivers that used those signals up
until then to calibrate time standards!) to include additional modulation
that would automatically set all of these "atomic" wall clocks once a day.
During the rest of the day the clock would run on its own crystal and keep
reasonably good time. I don't understand why your watch doesn't
automatically update to DST since I'm pretty sure Daylight Savings Time and
Standard Time information is part of the WWVB transmission. The only thing
you have to do when you get one of these clocks is choose your time zone
since WWVB doesn't have any way to know where you are (east or west) in the
US.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: Sunday, March 13, 2016 6:53 AM
To: TekScopes@...
Subject: Re: [TekScopes] Re: OT 10Mhz references

Dennis,-

Yeah, I read that story when I googled "time-nuts". Cool stuff. It got me to
wondering: If (as he demonstrated) time dilates with distance from the
gravity well of the earth, doesn't that make GPS based reference standards
inherently less accurate than earth based ones *on earth*? I'm sure the
smart folks worked out some sort of compensation for long-term effects.
Perhaps the GPS birds are receiving corrections from a ground station (in
which case, calibrating a ground-based oscillator to the bird would make it
run faster than it should). Or perhaps the GPS oscillators are running at a
slightly slower rate than earth-based ones, technically making them
inaccurate at their actual orbit.

Personally, back in the real world of doctor's appointments and bus
schedules, my house standard is a wrist-watch that sets itself from the
radio signal from Boulder every night. But it was out by an hour this
morning, since it was made before the powers that be changed the DST dates,
making the automatic DST setting useless. So I had to manually correct the
hour. When I set the clocks in my cars and house to DST this morning, I used
the watch as a reference and now all my clocks are within 0.5 minutes of
that signal, which should get me to work on time tomorrow morning. ;-)

On 12/03/2016 10:51 PM, 'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes]
wrote:

he took his kids camping for
a weekend to Paradise which is 7,000 feet up on Mt. Rainier near us in
Seattle. Of course Tom does things a little differently than the rest
of us.
He brought 3 HP Cesium Standards up with him on the trip. When he got
back down he compared the time dilation that occurred between the
three Cesium Standards up on the mountain for the weekend with the
ones he kept in his house which is almost at sea level. He then
calculated the expected time difference based on General Relativity.
------------------------------------
Posted by: Dwayne Verhey <tekscopes@...>
------------------------------------


Re: 7854 Repair & Restoration

 

On 13 Mar 2016 20:40:43 -0700, you wrote:

I cannot say that it is impossible that U50 went bad causing the
problem but I hoped it was something else like a cracked solder joint
or open resistor.
The open resistor theory still hasn't been ruled out. I'll try to see if I can catch anything by some common moding before and after various pairs of components and inducing the fault. Do you have some other ideas for ruling out the open resistor theory?
Measuring the DC voltages at various points in the circuit when it has
and has not failed may be enough to locate the fault. This needs to
be done with the readout off and the analog trace centered for best
results or disconnect the vertical amplifier inputs.

Replacing U50 can certainly be done but I do not know that anybody
knows the tuning procedure for adjusting R43, R47, L133, L163, and any
other selected parts. Transient response adjustment will be tricky to
impossible without a 7000 standardizer and reference level tunnel
diode pulser but I think you can get close enough for practical
purposes.
I'll see if I can land a standardizer sometime soon. I want one anyway. For the 7854, the "-01" model should do, right? Of course I'll try to obtain an "-02" or "-10", but I guess what I end up with will depend totally on what people feel like listing them for or bidding them up to.
My -00 is only rated to 200 MHz but it maxed out my 7854's bandwidth
but you are right, the 400 and 500 MHz mainframes would normally use
the -01 or faster standardizer. If you find a good deal, a -00 would
be better than nothing although they are pretty old; they use the
first generation of integrated RTL from Fairchild:

http://semiconductormuseum.com/MuseumStore/MuseumStore_Fairchild_923_Index.htm
http://www.swcomputingservices.com/hhhcorner.html

As fpr the reference level tunnel diode pulser, you're speaking of the 067-0681-01, right? I haven't lost faith that I'll be able to repair mine - even if I have to totally rebuild it. I have all of the parts it could possibly need down to the 9uf 125V wet tantalum cap.
Tektronix made a couple of suitable sources including that one. A
type 284 pulse generator would work.

Anyway, even with the fault, the scope is still working. At least I can "kick it back" into proper functionality when the circuit craps out on me. This way I have some time to obtain the things that I need to readjust the circuit if it really is U50 failing. That or find a whole 'nother vert amp board to put in it.


Re: 7854 RAM card upgrade only - any interest?

Cliff Carrie
 

In my manual (pre B100000), the A3 layout is Figure 7-25 on the back of diagram 17. C430 is identified just above the middle of P108 (between P108 and P430, which is a row of pins connecting through to the keybutton board).

However, on my A3 board there is no capacitor at that location! I therefore identified all of the caps shown on the layout drawing and the wiring diagram, and compared with the actual board. The board seems to match the layout drawing in all respects but one:


There is one unaccounted for cap. It is midway between P430 and U520, just about where the black hexagon identifying waveform test point 3 is located on the A3 layout drawing figure 7-25 with drawing id 2874-722A.


If we can establish through testing that C430 should never have been there, we could just cut pin 5 of P108, which might even be possible without removing the board from the scope - but we have to be sure first. Harder to reach, but less destructive would be to cut one lead of the mystery capacitor which is almost certainly C430.


Removing A3 from the scope looks like a huge disassembly job at first examination.


I disconnected P108 and tried to measure the capacitance between A3 pin 5 and ground - but my capacitance bridge insisted on oscillating unstably. It's never done that before. Maybe my test leads were a bit too long.


Cliff


Re: Tek 2247A [SN B029000] Recap and diode part list ?

Darren Ting
 

Hi David,

Thanks for your great advice.
looking at the colour in this area make me really worry.
Plan to do following:-
1. Replace all those big cap with 3-lead, it is so massive block the FAN air flow to reach CR2227 and CR2228 directly.  Due to this overheat and burn spot happen perhaps?
2. Film cap show hair line crack, need to replace, no exception.

3. Replace CR2227 and CR2228 with MUR160G and solder it with 1cm above the PCB service rather than touching the board [more expose to FAN air flow for cooler operation].



From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Monday, 14 March 2016, 11:34
Subject: Re: [TekScopes] Tek 2247A [SN B029000] Recap and diode part list ?

  I am not convinced that there is a problem at this point. Your
initial post said that the oscilloscope works fine and you just want
to preventatively change the aluminum electrolytic capacitors before
they fail which seems reasonable to me.

Any burn spot in the printed circuit board would be immediately under
or adjacent to the hot part. Maybe the board just has a colored area
from fabrication.

This part of the circuit is on the line side of the transformer so I
would not want to poke around in it with my finger checking for
temperature. A low mass temperature probe or IR thermometer would be
handy.

Most of the heat is going to come from Q2214 which operates as a
linear regulator. The +44.0 volt supply voltage to the inverter
across C2203 is important for high efficiency; if it is correct then I
do not think there is anything to worry about on the primary side.

The normal cause for overheating is a shorted diode on the secondary
side.

On Mon, 14 Mar 2016 01:50:27 +0000 (UTC), you wrote:

Hi David,
Thanks, yes you are right, reverse voltage drop of CR2227 and CR2228 actually belong to base-emitter junctions of Q2209 and Q2210 after re-look a the circuit diagram.
Now I really lost what to do next.

Any advice why this area get so hot till cause a scorch mark on PCB?

I have the picture but not sure how to attached it in here
#yiv2387202882 #yiv2387202882 -- #yiv2387202882ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv2387202882 #yiv2387202882ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv2387202882 #yiv2387202882ygrp-mkp #yiv2387202882hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv2387202882 #yiv2387202882ygrp-mkp #yiv2387202882ads {margin-bottom:10px;}#yiv2387202882 #yiv2387202882ygrp-mkp .yiv2387202882ad {padding:0 0;}#yiv2387202882 #yiv2387202882ygrp-mkp .yiv2387202882ad p {margin:0;}#yiv2387202882 #yiv2387202882ygrp-mkp .yiv2387202882ad a {color:#0000ff;text-decoration:none;}#yiv2387202882 #yiv2387202882ygrp-sponsor #yiv2387202882ygrp-lc {font-family:Arial;}#yiv2387202882 #yiv2387202882ygrp-sponsor #yiv2387202882ygrp-lc #yiv2387202882hd {margin:10px 0px;font-weight:700;font-size:78%;line-height:122%;}#yiv2387202882 #yiv2387202882ygrp-sponsor #yiv2387202882ygrp-lc .yiv2387202882ad {margin-bottom:10px;padding:0 0;}#yiv2387202882 #yiv2387202882actions {font-family:Verdana;font-size:11px;padding:10px 0;}#yiv2387202882 #yiv2387202882activity {background-color:#e0ecee;float:left;font-family:Verdana;font-size:10px;padding:10px;}#yiv2387202882 #yiv2387202882activity span {font-weight:700;}#yiv2387202882 #yiv2387202882activity span:first-child {text-transform:uppercase;}#yiv2387202882 #yiv2387202882activity span a {color:#5085b6;text-decoration:none;}#yiv2387202882 #yiv2387202882activity span span {color:#ff7900;}#yiv2387202882 #yiv2387202882activity span .yiv2387202882underline {text-decoration:underline;}#yiv2387202882 .yiv2387202882attach {clear:both;display:table;font-family:Arial;font-size:12px;padding:10px 0;width:400px;}#yiv2387202882 .yiv2387202882attach div a {text-decoration:none;}#yiv2387202882 .yiv2387202882attach img {border:none;padding-right:5px;}#yiv2387202882 .yiv2387202882attach label {display:block;margin-bottom:5px;}#yiv2387202882 .yiv2387202882attach label a {text-decoration:none;}#yiv2387202882 blockquote {margin:0 0 0 4px;}#yiv2387202882 .yiv2387202882bold {font-family:Arial;font-size:13px;font-weight:700;}#yiv2387202882 .yiv2387202882bold a {text-decoration:none;}#yiv2387202882 dd.yiv2387202882last p a {font-family:Verdana;font-weight:700;}#yiv2387202882 dd.yiv2387202882last p span {margin-right:10px;font-family:Verdana;font-weight:700;}#yiv2387202882 dd.yiv2387202882last p span.yiv2387202882yshortcuts {margin-right:0;}#yiv2387202882 div.yiv2387202882attach-table div div a {text-decoration:none;}#yiv2387202882 div.yiv2387202882attach-table {width:400px;}#yiv2387202882 div.yiv2387202882file-title a, #yiv2387202882 div.yiv2387202882file-title a:active, #yiv2387202882 div.yiv2387202882file-title a:hover, #yiv2387202882 div.yiv2387202882file-title a:visited {text-decoration:none;}#yiv2387202882 div.yiv2387202882photo-title a, #yiv2387202882 div.yiv2387202882photo-title a:active, #yiv2387202882 div.yiv2387202882photo-title a:hover, #yiv2387202882 div.yiv2387202882photo-title a:visited {text-decoration:none;}#yiv2387202882 div#yiv2387202882ygrp-mlmsg #yiv2387202882ygrp-msg p a span.yiv2387202882yshortcuts {font-family:Verdana;font-size:10px;font-weight:normal;}#yiv2387202882 .yiv2387202882green {color:#628c2a;}#yiv2387202882 .yiv2387202882MsoNormal {margin:0 0 0 0;}#yiv2387202882 o {font-size:0;}#yiv2387202882 #yiv2387202882photos div {float:left;width:72px;}#yiv2387202882 #yiv2387202882photos div div {border:1px solid #666666;height:62px;overflow:hidden;width:62px;}#yiv2387202882 #yiv2387202882photos div label {color:#666666;font-size:10px;overflow:hidden;text-align:center;white-space:nowrap;width:64px;}#yiv2387202882 #yiv2387202882reco-category {font-size:77%;}#yiv2387202882 #yiv2387202882reco-desc {font-size:77%;}#yiv2387202882 .yiv2387202882replbq {margin:4px;}#yiv2387202882 #yiv2387202882ygrp-actbar div a:first-child {margin-right:2px;padding-right:5px;}#yiv2387202882 #yiv2387202882ygrp-mlmsg {font-size:13px;font-family:Arial, helvetica, clean, sans-serif;}#yiv2387202882 #yiv2387202882ygrp-mlmsg table {font-size:inherit;font:100%;}#yiv2387202882 #yiv2387202882ygrp-mlmsg select, #yiv2387202882 input, #yiv2387202882 textarea {font:99% Arial, Helvetica, clean, sans-serif;}#yiv2387202882 #yiv2387202882ygrp-mlmsg pre, #yiv2387202882 code {font:115% monospace;}#yiv2387202882 #yiv2387202882ygrp-mlmsg * {line-height:1.22em;}#yiv2387202882 #yiv2387202882ygrp-mlmsg #yiv2387202882logo {padding-bottom:10px;}#yiv2387202882 #yiv2387202882ygrp-msg p a {font-family:Verdana;}#yiv2387202882 #yiv2387202882ygrp-msg p#yiv2387202882attach-count span {color:#1E66AE;font-weight:700;}#yiv2387202882 #yiv2387202882ygrp-reco #yiv2387202882reco-head {color:#ff7900;font-weight:700;}#yiv2387202882 #yiv2387202882ygrp-reco {margin-bottom:20px;padding:0px;}#yiv2387202882 #yiv2387202882ygrp-sponsor #yiv2387202882ov li a {font-size:130%;text-decoration:none;}#yiv2387202882 #yiv2387202882ygrp-sponsor #yiv2387202882ov li {font-size:77%;list-style-type:square;padding:6px 0;}#yiv2387202882 #yiv2387202882ygrp-sponsor #yiv2387202882ov ul {margin:0;padding:0 0 0 8px;}#yiv2387202882 #yiv2387202882ygrp-text {font-family:Georgia;}#yiv2387202882 #yiv2387202882ygrp-text p {margin:0 0 1em 0;}#yiv2387202882 #yiv2387202882ygrp-text tt {font-size:120%;}#yiv2387202882 #yiv2387202882ygrp-vital ul li:last-child {border-right:none !important;}#yiv2387202882


Re: 7854 Repair & Restoration

Brian Bloom
 

I cannot say that it is impossible that U50 went bad causing the
>problem but I hoped it was something else like a cracked solder joint
>or open resistor.


The open resistor theory still hasn't been ruled out. I'll try to see if I can catch anything by some common moding before and after various pairs of components and inducing the fault. Do you have some other ideas for ruling out the open resistor theory?

>Replacing U50 can certainly be done but I do not know that anybody
>knows the tuning procedure for adjusting R43, R47, L133, L163, and any
>other selected parts. Transient response adjustment will be tricky to
>impossible without a 7000 standardizer and reference level tunnel
>diode pulser but I think you can get close enough for practical
>purposes.

I'll see if I can land a standardizer sometime soon. I want one anyway. For the 7854, the "-01" model should do, right? Of course I'll try to obtain an "-02" or "-10", but I guess what I end up with will depend totally on what people feel like listing them for or bidding them up to.

As fpr the reference level tunnel diode pulser, you're speaking of the 067-0681-01, right? I haven't lost faith that I'll be able to repair mine - even if I have to totally rebuild it. I have all of the parts it could possibly need down to the 9uf 125V wet tantalum cap.

Anyway, even with the fault, the scope is still working. At least I can "kick it back" into proper functionality when the circuit craps out on me. This way I have some time to obtain the things that I need to readjust the circuit if it really is U50 failing. That or find a whole 'nother vert amp board to put in it.


Re: Tek 2247A [SN B029000] Recap and diode part list ?

 

I am not convinced that there is a problem at this point. Your
initial post said that the oscilloscope works fine and you just want
to preventatively change the aluminum electrolytic capacitors before
they fail which seems reasonable to me.

Any burn spot in the printed circuit board would be immediately under
or adjacent to the hot part. Maybe the board just has a colored area
from fabrication.

This part of the circuit is on the line side of the transformer so I
would not want to poke around in it with my finger checking for
temperature. A low mass temperature probe or IR thermometer would be
handy.

Most of the heat is going to come from Q2214 which operates as a
linear regulator. The +44.0 volt supply voltage to the inverter
across C2203 is important for high efficiency; if it is correct then I
do not think there is anything to worry about on the primary side.

The normal cause for overheating is a shorted diode on the secondary
side.

On Mon, 14 Mar 2016 01:50:27 +0000 (UTC), you wrote:

Hi David,
Thanks, yes you are right, reverse voltage drop of CR2227 and CR2228 actually belong to base-emitter junctions of Q2209 and Q2210 after re-look a the circuit diagram.
Now I really lost what to do next.

Any advice why this area get so hot till cause a scorch mark on PCB?

I have the picture but not sure how to attached it in here


Re: 7854 Repair & Restoration

 

On 13 Mar 2016 19:42:25 -0700, you wrote:

It did not fix the problem. Hmmm.....

I'll go through the voltages around the vertical amp board tomorrow. I need to try and sleep off the rest of this sinus infection.

What do you think the chances are that U50 is going bad? I suppose it couldn't hurt to have a spare anyway... I can just buy one, swap it, and see.
I cannot say that it is impossible that U50 went bad causing the
problem but I hoped it was something else like a cracked solder joint
or open resistor.

Replacing U50 can certainly be done but I do not know that anybody
knows the tuning procedure for adjusting R43, R47, L133, L163, and any
other selected parts. Transient response adjustment will be tricky to
impossible without a 7000 standardizer and reference level tunnel
diode pulser but I think you can get close enough for practical
purposes.