PG506 Repair - I had a Great Day today/


Michael W. Lynch
 

Several years ago I bought a PG506 (B40000 and up) along with other TM500 plug ins. I was unlucky enough to damage the PG506 by installing it in a TM506 that had a bad pass transistor. For whatever reason this caused a series of failures in the Standard Amplitude Section, including a non-functional display. I have been sitting on this thing and trying to repair it (on and off) since that time (3 years?). I asked for some advice about this repair, but nothing that was suggested seemed to help. In the past few weeks I was able to obtain a mostly working PG506 and easily repair it, so I started back on the older and more seriously damaged unit.as a COVID project. Using my newer working unit as a guide, I was able to check the non- working unit against the known good unit. After a couple of days and several bad components, I have restored it to functional status.

All that is left now is to go through the calibration process on both units. Went from having Zero working to having two working is what I call a good week.

I found these components bad in the unit.

Q435 151-0223-00 NPN
Q535 151-0223-00 NPN
U460 156-0067-00 OP amp (741CN)
U200 156-0067-00 OP amp (741CN)
U240 156-0067-00 OP amp (741CN)
U610 156-0039-00 Dual J-K Flip-Flop
U480 156-0399-00 Opto Coupler
U255 156-0399-00 Opto Coupler
CR290 152-0141-02 (1N4152R)
CR291 152-0141-02 (1N4152R)

This was possible only because of the education that I have received from this group. Thanks to everyone who has help my hand through many of my other questions.
--
Michael Lynch
Dardanelle, AR


 

It's always a good day when you manage to repair something.

So is it common practice, in this hobby, to sit on instruments waiting for your own skills to ripen?

I'm currently doing that with a couple of instruments: I'm quite unripe.

-- Jeff Dutky


 

Congrats, Michael, well done! We'd all be much less happy if it weren't for broken equipment.

Raymond


toby@...
 

On 2021-04-19 4:26 p.m., Jeff Dutky wrote:
It's always a good day when you manage to repair something.

So is it common practice, in this hobby, to sit on instruments waiting for your own skills to ripen?
Well, this is kind of what I am doing. I went from having repaired zero
scopes to having got four or five Tek & HP XY's working -- relatively
easy starter repairs.

The instruments waiting for me to smarten up are much more challenging,
mainly a 466 that died while I was testing it out, and an HP 1746.

--Toby


I'm currently doing that with a couple of instruments: I'm quite unripe.

-- Jeff Dutky





Paul Amaranth
 

Nice to hear positive results

Dug myself into a deeper hole on a LeCroy repair by blowing up the
power supply. It is very poorly documented and I was trying to
understand how the protection circuitry worked when I managed to
blow it up. It's been sitting on the bench for a couple weeks.
I'll get back to it after some higher priority jobs get done.

Maybe I'll have a better idea of how to procede by then.

Paul

On Mon, Apr 19, 2021 at 01:26:41PM -0700, Jeff Dutky wrote:
It's always a good day when you manage to repair something.

So is it common practice, in this hobby, to sit on instruments waiting for your own skills to ripen?

I'm currently doing that with a couple of instruments: I'm quite unripe.

-- Jeff Dutky
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows


Tom Lee
 

Congratulations, Michael! Those are nice gens, so having two working ones is great. I’ve never seen such a large collection of blown components in a single unit. Your persistence paid off!

Cheers
Tom

Sent from my iThing, so please forgive brevity and typos

On Apr 19, 2021, at 12:43, Michael W. Lynch via groups.io <mlynch003=yahoo.com@groups.io> wrote:

Several years ago I bought a PG506 (B40000 and up) along with other TM500 plug ins. I was unlucky enough to damage the PG506 by installing it in a TM506 that had a bad pass transistor. For whatever reason this caused a series of failures in the Standard Amplitude Section, including a non-functional display. I have been sitting on this thing and trying to repair it (on and off) since that time (3 years?). I asked for some advice about this repair, but nothing that was suggested seemed to help. In the past few weeks I was able to obtain a mostly working PG506 and easily repair it, so I started back on the older and more seriously damaged unit.as a COVID project. Using my newer working unit as a guide, I was able to check the non- working unit against the known good unit. After a couple of days and several bad components, I have restored it to functional status.

All that is left now is to go through the calibration process on both units. Went from having Zero working to having two working is what I call a good week.

I found these components bad in the unit.

Q435 151-0223-00 NPN
Q535 151-0223-00 NPN
U460 156-0067-00 OP amp (741CN)
U200 156-0067-00 OP amp (741CN)
U240 156-0067-00 OP amp (741CN)
U610 156-0039-00 Dual J-K Flip-Flop
U480 156-0399-00 Opto Coupler
U255 156-0399-00 Opto Coupler
CR290 152-0141-02 (1N4152R)
CR291 152-0141-02 (1N4152R)

This was possible only because of the education that I have received from this group. Thanks to everyone who has help my hand through many of my other questions.
--
Michael Lynch
Dardanelle, AR





tek_547
 

Thanx Michael for your detailed repair summary. My PG506 (also >B40000) functions normal but only has a strange display behaviour; when switched on STD AMPL. (and VAR AMPL. out) and rotating the VAR AMPL. only the HIGH led is continuous lighting and the LOW led never goes on. The (variable) values of the output signal varies normal up and down when rotating the VAR knob
Also the display is not given the actual value of the setting. I changed almost everything but it is difficult to understand and to troubleshoot it, so with your information maybe I got a step further.

René Stay safe and maybe you have any suggestions.


Michael W. Lynch
 

On Mon, Apr 19, 2021 at 04:47 PM, Tom Lee wrote:


I’ve never seen such a large collection of blown components in a single
unit. Your persistence paid off!
Tom,
Thanks! I think this is what made the repair so difficult.

For clarification, and after thinking back, I recalled that this was the plug in where i mistakenly inverted my flexible extender and likely damaged more than a "normal" complement of parts. I did plug it into the TM506 with a "bad" pass transistor, (the trouble started there) but the bone headed error of inverting the extender greatly exacerbated the damage. This was a teaching moment for me, from that point on, I NEVER plug in a flexible extender without triple checking for correct orientation. This was also my inspiration for building the TM500 Tester Project.

Bottom line is that what I have learned from this group made it possible to recover the instrument, in spite of my early "ham fisted" effort to the contrary.

Sincerely,

--
Michael Lynch
Dardanelle, AR


Michael W. Lynch
 

On Tue, Apr 20, 2021 at 04:56 AM, tek_547 wrote:


René Stay safe and maybe you have any suggestions.
René,

Thanks for your kind response.

Perhaps I can help as this was my problem as well.

Would you be so kind as to tell me what parts you have already changed?

Do you see the "88" when you push the "variable" in?
Does the amplitude of the waveform respond to turning the "variable" knob or remain fixed at one level?
Do the amplitudes generated in each switch position agree with the selected value of the switch across all positions?

I will be glad to try to give some ideas from there.

Sincerely,

--
Michael Lynch
Dardanelle, AR


-
 

Since shorted pass transistors in the TM 50xs are so common, I wonder
if it would be a good idea to add either an overload prevention circuit,
i.e. a fuse, or an over voltage detection circuit and output cutoff to to
the extender cards? A simple SCR crowbar circuit with a fuse would be
enough to prevent damage to anything plugged into the extender.

On Tue, Apr 20, 2021 at 9:07 AM Michael W. Lynch via groups.io <mlynch003=
yahoo.com@groups.io> wrote:

On Mon, Apr 19, 2021 at 04:47 PM, Tom Lee wrote:


I’ve never seen such a large collection of blown components in a single
unit. Your persistence paid off!
Tom,
Thanks! I think this is what made the repair so difficult.

For clarification, and after thinking back, I recalled that this was the
plug in where i mistakenly inverted my flexible extender and likely damaged
more than a "normal" complement of parts. I did plug it into the TM506
with a "bad" pass transistor, (the trouble started there) but the bone
headed error of inverting the extender greatly exacerbated the damage.
This was a teaching moment for me, from that point on, I NEVER plug in a
flexible extender without triple checking for correct orientation. This
was also my inspiration for building the TM500 Tester Project.

Bottom line is that what I have learned from this group made it possible
to recover the instrument, in spite of my early "ham fisted" effort to the
contrary.

Sincerely,

--
Michael Lynch
Dardanelle, AR






 

Michael W. Lynch wrote:

For clarification, and after thinking back, I recalled that this was the plug in where
I mistakenly inverted my flexible extender and likely damaged more than a "normal"
complement of parts. I did plug it into the TM506 with a "bad" pass transistor, (the
trouble started there) but the bone headed error of inverting the extender greatly
exacerbated the damage.
The extenders really should be keyed at least between positions 5 and 6. I realize that doing that would mean that you couldn't use a TM500 extender in the 5000-series oscilloscopes, but that's a small price to pay for not blowing up expensive equipment.

The fact that TM500/TM5000 mainframes and 5000-series scopes share the same physical form-factor (modulo some keying slots) is tragic.The electrical specifications are not compatible, but I've seen several 5000-series scopes on eBay with TM500 modules in the holes. In the best case the plug-in has not bee pushed in all the way, but in the worst case physical damage has been done to eiher the scope or the plug-in (or both).

I don't understand why Tek didn't either make the plug-in interfaces compatible, or use different enough physical form-factors to prevent plugging wrong things into wrong things. I know that there are a number of TM500 plug-ins that can take input from (and send output to) the backplane; it would have been really useful to be able to plug a counter/timer or a DMM into a 5000-series scope and take measurements on an input waveform.

-- Jeff Dutky


Harvey White
 

The design idea for the TM500 series was any number of power supply configurations followed by a blank area where various connections could be brought out to the backplane.  The remaining connections (other than power) were therefore defined per module, and likely all were used.

The  5000 series scopes had very different power supply requirements, and did not (IIRC) make their own power in the module (might have, but it would be quite rare).  If TEK used the "bottom" connections on the TM500 pinout for the 5000 scopes, you'd preclude the backplane connections in the 500 series.

As to the physical construction of the 5000 series, those scopes were designed as low cost (for Tek!) low bandwidth scopes, hardly the equivalent of the 7000 series.  I suspect that the designers were told to keep the cost low, period.  One reason, perhaps, that the 7CT1n/5CT1n plugins had the same dials (5000 style, sadly), no readouts, and there was an adaptor board in there somewhere, either 5000 to 7000 or 7000 to 5000, or am I thinking of the sampling plugins?

Harvey

On 4/20/2021 11:02 AM, Jeff Dutky wrote:
Michael W. Lynch wrote:
For clarification, and after thinking back, I recalled that this was the plug in where
I mistakenly inverted my flexible extender and likely damaged more than a "normal"
complement of parts. I did plug it into the TM506 with a "bad" pass transistor, (the
trouble started there) but the bone headed error of inverting the extender greatly
exacerbated the damage.
The extenders really should be keyed at least between positions 5 and 6. I realize that doing that would mean that you couldn't use a TM500 extender in the 5000-series oscilloscopes, but that's a small price to pay for not blowing up expensive equipment.

The fact that TM500/TM5000 mainframes and 5000-series scopes share the same physical form-factor (modulo some keying slots) is tragic.The electrical specifications are not compatible, but I've seen several 5000-series scopes on eBay with TM500 modules in the holes. In the best case the plug-in has not bee pushed in all the way, but in the worst case physical damage has been done to eiher the scope or the plug-in (or both).

I don't understand why Tek didn't either make the plug-in interfaces compatible, or use different enough physical form-factors to prevent plugging wrong things into wrong things. I know that there are a number of TM500 plug-ins that can take input from (and send output to) the backplane; it would have been really useful to be able to plug a counter/timer or a DMM into a 5000-series scope and take measurements on an input waveform.

-- Jeff Dutky





Michael W. Lynch
 

On Tue, Apr 20, 2021 at 10:02 AM, Jeff Dutky wrote:


The extenders really should be keyed at least between positions 5 and 6. I
realize that doing that would mean that you couldn't use a TM500 extender in
the 5000-series oscilloscopes, but that's a small price to pay for not blowing
up expensive equipment.
Jeff,

This was just a rookie mistake. Had I invoked the old carpenter's adage "measure twice, cut once" (in this case "look twice, connect once"), I would have been OK. The extenders are clearly marked "MODULE TOP" and the gentleman that I bought them from warned me to pay close attention to that "TOP" marking. Even so, I got in too big a big hurry and made a terrible mistake.

You are correct, had the extender been keyed, it certainly would have prevented my error. Although, had I simply slowed down and looked at what I was doing, instead of "assuming" my connection was right, I would have not screwed up.

The "silver lining" of this mistake was that it taught me a much more valuable lesson, one that I apply to many other situations. That is, look closely at ANY cable connections, not just extenders before you turn on the power. I have found some instruments where the repair was as simple as a interconnect cable being connected "backwards" on one end.

Sincerely,

--
Michael Lynch
Dardanelle, AR


 

Harvey White wrote:

One reason, perhaps, that the 7CT1n/5CT1n plugins had the same dials (5000 style, sadly),
no readouts, and there was an adaptor board in there somewhere, either 5000 to 7000 or
7000 to 5000, or am I thinking of the sampling plugins?
I think that's only the 5S14N/7S14(N). The 7CT1N does have a daughter board for the card edge connector, but the main board is full-length, so it would not fit in 5000-series plug-in. It's odd though: the 5CT1N and 7CT1N seem to have essentially the same specs, not just the same front-panel layout. It really would have been smart to use the 5CT1N board in the 7CT1N with a longer daughter board for the card edge connector.

There is a lot about Tek's design and manufacturing philosophy that I find baffling, but my viewpoint is steeped in post-70s American mass-market thinking, which was largely a reaction to lower cost/higher quality products flowing in from Asia. I know that Tek made a bunch of changes for the same reasons (e.g. the 2200-series scopes), but you just can't apply the same concepts to high-end test equipment that you do to mass-market manufacturing.

-- Jeff Dutky


Harvey White
 

or perhaps you *shouldn't* apply some of those philosophies.

I suspect it made Tek what it is today.

Harvey

On 4/20/2021 12:41 PM, Jeff Dutky wrote:
Harvey White wrote:
One reason, perhaps, that the 7CT1n/5CT1n plugins had the same dials (5000 style, sadly),
no readouts, and there was an adaptor board in there somewhere, either 5000 to 7000 or
7000 to 5000, or am I thinking of the sampling plugins?
I think that's only the 5S14N/7S14(N). The 7CT1N does have a daughter board for the card edge connector, but the main board is full-length, so it would not fit in 5000-series plug-in. It's odd though: the 5CT1N and 7CT1N seem to have essentially the same specs, not just the same front-panel layout. It really would have been smart to use the 5CT1N board in the 7CT1N with a longer daughter board for the card edge connector.

There is a lot about Tek's design and manufacturing philosophy that I find baffling, but my viewpoint is steeped in post-70s American mass-market thinking, which was largely a reaction to lower cost/higher quality products flowing in from Asia. I know that Tek made a bunch of changes for the same reasons (e.g. the 2200-series scopes), but you just can't apply the same concepts to high-end test equipment that you do to mass-market manufacturing.

-- Jeff Dutky





Michael W. Lynch
 

On Mon, Apr 19, 2021 at 04:10 PM, Paul Amaranth wrote:


Dug myself into a deeper hole
Paul,

That is what I did with this 506. On top of inserting it into a defective TM506, I also managed to connect my flexible extender connector "upside down" and burned up even more stuff. I bought this thing as part of a loaded TM506 that was "working" (NOT!). I have made 5 or 6 attempts to repair it and always get bogged down and have to put it aside. That was over 3 years ago and my knowledge level has increased to the point that I finally got it fixed. You can only look at a project for so long, before you lose focus. Putting such things aside often results in a revelation or at least reduced irritation of your proverbial "last nerve".

--
Michael Lynch
Dardanelle, AR


 

Harvey White wrote:

or perhaps you *shouldn't* apply some of those philosophies.

I suspect it made Tek what it is today.
I suspect that you are right. It's not my impression that Tek ever left any money on the table, and I don't ever recall them being referred to as "beleaguered" at any point during my conscious existence. It also does not appear that their customer base was ever dissatisfied with their products (features or price).

It just bothers me that the 5000-series scopes and the TM500 modules are so similar but actually incompatible. I can't find it now, but I saw a 5000-series scope on the auction site with a TM500 modules stuffed in the center hole. Someone must have bought those poor, abused instruments.

-- Jeff Dutky


tek_547
 

Hi Michael, thanx for your time and trying to help me with solving my problematic PG506.
When "I push the variable in" I see the "88" with the decimal point in the middle.
I said before that only the HIGH led is continue working but that is not correct. It is the LOW led that is allways on so sorry about that.
The output signal of the PG506 is functioning fully normal, and also "variable" is working correct. The problem is only the display. A bit erratic; sometimes steady and sometimes all segments are glowing when turning the variable.
So at your questions if the amplitude of the waveform respond to turning the "variable" knob or remain fixed at one level? and "Do the amplitudes generated in each switch position agree with the selected value of the switch across all positions?" I can say that these functions normal.

All the capacitors in the power supply and other boards of the PG506 are recapped, so power supply´s are normal. But the 5V1 at the collector from Q70 is a bit low; about 4,75V The 5V from the power supply schematic 1 (lower left corner) is 5,03V so this looks normal.
Is on yours PG506 the 5V also a bit low after Q70 ? Maybe this is important.

The parts that I changed is a long list so here we go:
U665, 666, 667 and 668 changed (no difference)
U670 and U671 changed (no difference)
U673 and U675 changed (no difference)
U615 changed (no difference)
U430 and U460 changed (no difference)
U470 changed (no difference)
U400 changed (no difference)
Furthermore are most of the transistors checked so that there are no shorts.
And also maybe interesting is the fact that T130 in the power supply is about 70°C when the STD AMP switch is activated. So not possible to you put your finger on it.
When it is on FAST RISE or HIGH AMPL. the temperature is more normal (about 45°C).
Has your PG506 the same behaviour about the temp from T130?

So the few things I did not changed are;
The display board A4 (a bit clumsy to remove) and the two opto couplers U480 and U255 (do you have a substitute number for that type?)
I think the problem is in the display section (board A4) or in the digital voltmeter circuit (schematic 3) but maybe you have other suggestions.

I´m glad to hear what you think about and maybe I get it work normal after a while, René


Michael W. Lynch
 

On Wed, Apr 21, 2021 at 03:51 AM, tek_547 wrote:

René,

Good day!

You have done a lot of work, way more that I have done. Thanks for the details, this eliminates some of the thing that could have effected your unit.

Balance of reply is INTERLEAVED below

When "I push the variable in" I see the "88" with the decimal point in the middle.
This is Good and Normal. Indicates that the LED are capable of function once the proper signals are restored.

I said before that only the HIGH led is continue working but that is not
correct. It is the LOW led that is all ways on so sorry about that.
ANSWER: Not a problem, that will likely be cured along with the display function.

But the 5V1 at the collector from Q70
is a bit low; about 4,75V The 5V from the power supply schematic 1 (lower left
corner) is 5,03V so this looks normal.
Is on yours PG506 the 5V also a bit low after Q70 ? Maybe this is important.
This Should not be a problem, I will check mine to confirm voltages at this point. I believe that they are using Q70 as a on/off switch for the display when in "Std. Amplitude Variable mode".

The parts that I changed is a long list so here we go:
U665, 666, 667 and 668 changed (no difference)
U670 and U671 changed (no difference)
U673 and U675 changed (no difference)
U615 changed (no difference)
U430 and U460 changed (no difference)
U470 changed (no difference)
U400 changed (no difference)
Furthermore are most of the transistors checked so that there are no shorts.
ANSWER: WOW! This is a HUGE list. Specifically on U400, have you checked for wave forms at the various pins of your "New" U400. If you have pins stuck High or Low (missing wave forms), then your problem is obviously before or after that IC. Check to see that you have wave forms at pins 1~6 and pins 8~13. Probe carefully to avoid shorting between pins. Pin #7 is Ground and Pin#14 is 5V Supply. All other pins will have some sort of pulse train if the instrument is working correctly (sans the display).

Did you confirm that the other remaining 156-0067-00 (741CN) op amps are all good? These would be U50, U200, U240,U330, U375 in addition to the two that you already changed. Most of these are in sockets, so they are not a major problem to change. I also added sockets for U200,U240,U255 and U480 at the time these were replaced. I cannot say for sure that U255 and U480 (opto-couplers) were bad, however I had the board out and the desoldering pump hot, so it was a simple task to remove them, add sockets and install new 4N27's.

Regarding transistors, I found two 151-0223-00 NPN (Q435 and Q535) that were bad on my unit and they were the final two pieces that restored the unit to operation. I have the luxury of a Type 576 Curve tracer for testing, but you can test these and see if they are bad or not by other methods. I replaced these with 2N3904 parts and they worked just fine. Confirm the 4V 1kHz square wave pulse signal at Pin #8 U400 then look for that same signal at R532, then on the base of Q535. Remove and check Q535. I suspect that you will find Q535 to be defective.

You made no mention of diodes, you would be wise to check all the diodes and confirm they are good. I found a couple of bad ones early on. Those were all 152-0141-02 (1N4152R) which had failed.

And also maybe interesting is the fact that T130 in the power supply is about
70°C when the STD AMP switch is activated. So not possible to you put your
finger on it.
When it is on FAST RISE or HIGH AMPL. the temperature is more normal (about
45°C).
Has your PG506 the same behaviour about the temp from T130?
ANSWER: I will need to check this out.and report back. I do not remember mine being hot.

So the few things I did not changed are;
The display board A4 (a bit clumsy to remove) and the two opto couplers U480
and U255 (do you have a substitute number for that type?)
ANSWER: 156-0399-00 Opto Couplers are 4N27. You can find these and many more useful cross references in the TEKTRONIX SEMICONDUCTOR Common Design Parts Catalog, Available at TEKWIKI
link: http://w140.com/Tektronix_Xref_sm.pdf

I think the problem is in the display section (board A4) or in the digital
voltmeter circuit (schematic 3) but maybe you have other suggestions.
ANSWER: I am thinking a bad diode or transistor.

I´m glad to hear what you think about and maybe I get it work normal after a
while, René
Anything that is not clear, please ask me to elaborate. Sometimes I am lacking in my explanations.

Sincerely,

--
Michael Lynch
Dardanelle, AR


tek_547
 

That is really a very detailed explanation Michael, very much thanx for that! In the weekend or next week I have the time to work on the PG506 because the coming days I´m busy with other things.
Working and measuring on the PG506 need all your attention (floating ground) so I must have time for it.
You gave me more than enough things to sort out that I can check, so when I know more I give a reply.

Furthermore thanks for your effort and next week hopefully I know more, René