Date   
Re: Tek 2467B

Michael A. Terrell
 

Chuck said that the Sample & Hold capacitor could affect calibration, not electrolytics.


Michael A. Terrell

--

-----Original Message-----
From: "Robert Calk Jr." <@RobertC>
Sent: Oct 14, 2018 10:35 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 2467B

Hi Dennis,

I was hoping that I misread it... I'm just a hobbyist. If yall can't find a workaround, then I'm not even going to try. But the caps have to be replaced. I guess I'll just have to buy the equipment and learn how to calibrate my scope myself, or use it for target practice and chalk it up as a loss. It seems like the scope could make allowances or self correct about something as simple as changing a few caps.

I guess I should not have listened to Dave and just went digital from the beginning. I don't understand why changing a few caps would mess up the calibration - it doesn't make any sense to me. But I don't know much about working on scopes.

Re: Tek 2467B

 

-----Original Message-----
From: Robert Calk Jr.
Sent: Sunday, October 14, 2018 7:35 PM

<snip>
It seems like the scope could make allowances or self correct
about something as simple as changing a few caps.
Hi Robert,
Yes, it would be nice if that was the case. Some of the newer scopes, and even some of the now 30 year old Tek 11000 series scopes can self-calibrate. But to understand why this was so difficult to do until 30 years ago would take a quite a lot of theory and study.

The fastest way for you to discover how difficult this is to do would be to get yourself a BSEE degree and then spend another 10+ years working in the electronic test equipment field. At that point I suspect that if I showed you your posts regarding how simple it SHOULD be to make a self-calibrating instrument you would laugh out loud.

It is easy to ask why isn't every instrument self-calibrating until you find out why it required new discoveries, thousands of patents, teams of brilliant people, and tens of thousands of man hours to figure out how to do this.

Why don't you see it everywhere? Tek figured out to make some of the 11000 series scopes self-calibrate over 30 years ago, but even 30 years later very few things in life are self-calibrating. Why is that?

Dennis Tillman W7PF






--
Dennis Tillman W7PF
TekScopes Moderator

Re: 2445A calibration

Tom Gardner
 

On 14/10/18 23:39, Raymond Domp Frank wrote:
On Sat, Oct 13, 2018 at 03:08 PM, <maxim.vlasov@...> wrote:

Hi Maxim,

Hello Raymond,

I see the comment ;) Well we are not jailbreaking the new iPhone herein with
all the possible and impossible protection switched on ;))

Well, we can start it in a few ways.
I see that you're making progress. I have been using my Logic Analyzers (!) (Tek TLA715, HP16702B) recently in an effort to follow the instruction flow in an 80C186-based low-frequency spectrum analyzer (Stanford Scientific SR760). The out-of sequence/pipeline architecture makes that task a lot more difficult than when I was having fun using my HP 1615A logic analyzer while developing 6802 systems 30 years ago.
Good luck and have fun with this project!
Exactly. I remember, also exactly 30 years ago, having the same
problem with a 68020, and thinking it was a pain compared to
Z80s 6 years earlier.

In my case I was debugging a commercial RTOS, and found that
a parameter supplied to one RTOS call was mutated when it
reappeared later. Oh, the fun we had when we were young.

come mai Tekscope mail list non si aggiorna piĆ¹?

Alessandro Cattaneo
 

Re: What is the meaning of ULU? Topic was: 7000-series power-hungry plug-ins

Leo Potjewijd
 

My best guess is an Unified (or Universal) Load Unit, something like a
calibrator for power supplies...

Just my EUR0.02.

Re: What is the meaning of ULU? Topic was: 7000-series power-hungry plug-ins

Leo Potjewijd
 

Oops. forgot all about the delay caused by the webmail digest...
Apologies for wasted BW.

Re: Tek 2467B

Chuck Harris
 

No, I said both could affect calibration. It all has to do with
what shape the scope was in for the previous calibration.

If the sample and hold cap was a bit leaky the last time it was
calibrated, replacing it with a good cap will restore its operation
and now the voltages it creates will be higher, thus invalidating
the last calibration.

Similarly, if a filter cap was letting through excess ripple during
the last calibration, the power supply settings would be incorporate
that ripple. Replace the capacitors and the excess ripple would be
gone, but the voltage will change by the average of the ripple.

It might not be a great affect, but it will be measurable.

These things are major repairs, and the manual is quite clear about
major repairs calling for a new calibration.

-Chuck Harris

Michael A. Terrell wrote:

Chuck said that the Sample & Hold capacitor could affect calibration, not electrolytics.


Michael A. Terrell

Re: Tek 2467B

Michael A. Terrell
 

How many people would calibrate a scope, before verifying the scope didn't have bad caps? The S/H cap would be the least likely to fail, compared to the average lifetime of the electrolytics. Also, most of the scopes ending up in private hands haven't been in a cal lab for years or even decades so recapping the electrolytics would return it to the condition it should have been in at the last calibration. At least, anything I repaired would have been done this way.

Leakage around the S/H circuit's capacitor could be affected by contamination on the circuit board, as well. A good cleaning should always be part of testing and calibrating very high impedance circuits, as you well know. :)

I too, have worked in electronics for decades. Over five of them including at the factory on systems that were only allowed a 1.5 mV error in a system with a 0 to 5V output in a complex AGC circuit comprised of 14 Op-Amps. One of these boards was part of a kU band communications system for the International Space Station.


Michael A. Terrell

-----Original Message-----
From: Chuck Harris <cfharris@...>
Sent: Oct 15, 2018 8:40 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 2467B

No, I said both could affect calibration. It all has to do with
what shape the scope was in for the previous calibration.

If the sample and hold cap was a bit leaky the last time it was
calibrated, replacing it with a good cap will restore its operation
and now the voltages it creates will be higher, thus invalidating
the last calibration.

Similarly, if a filter cap was letting through excess ripple during
the last calibration, the power supply settings would be incorporate
that ripple. Replace the capacitors and the excess ripple would be
gone, but the voltage will change by the average of the ripple.

It might not be a great affect, but it will be measurable.

These things are major repairs, and the manual is quite clear about
major repairs calling for a new calibration.

-Chuck Harris

Michael A. Terrell wrote:
Chuck said that the Sample & Hold capacitor could affect calibration, not electrolytics.

Re: Tek 2467B

Harvey White
 

On Sun, 14 Oct 2018 20:27:56 -0700, you wrote:

Hi Harvey,

I have read some of that stuff before, but this is the first time that I heard changing a few caps could mess up the calibration. My pulse rate is back to normal now. lol
Think of all the cardio exercise you got.

If you don't recalibrate, you should at least check the calibration.

Tektronix made a number of pieces of equipment for calibration use,
the "newer" TM500 units work well, and the TM5000 units are likely the
latest ones they made specifically for calibration.

Once you get into some of their digital scopes, the manual calibration
seems to be less preferred, and they go into an automated cal setup.


I really love this scope and it has the Television/Video option that might come in handy some day, among other options. Plus it looks brand new inside; like it has spent 90% of it's life boxed up in a non-smokers closet. I'm going to study the schematics and see if I can figure something out. If there is a way, I'll find it.
Remember that on the MCP tubes, the life of the MCP is limited, so
avoid high intensity operation. Opinions do vary on this.



I was planning on getting a digital scope anyway. I'll just have to get one sooner than I had planned because I believe it's better to have both also. Thanks for the info.
Unless you're in the 2xxx series for digital, there are a number of
scopes in the TDS series. IIRC, the TDS5xx, 6xx had possible
capacitor problems. The TDS7xx series apparently did not. Those are
decent scopes (I have a TDS540A), but would like to have color.

I'd go for a color one with an LCD if possible, the older liquid
crystal shutter does work, but the interface gel dries out (google
TDS544 repair for sordid details).

Nonetheless, while I have both 7000 series, 24xx digital, and a
TDS540A, I find that I use the 7904 and the TDS about equally. One
does not necessarily replace the other.

Since I do digital stuff with FPGAs, I figured I'd need the bandwidth
(500 mhz, 4 channels). I have a logic analyzer to further work with
the high speed logic.

Harvey




Re: Tek 2467B

Chuck Harris
 

How many people would simply slap a calibration sticker
on a scope and charge for the calibration?

Using yourself as the minimum standard by which all
technicians, and calibration shops, operate is rather
fallacious.

That most of theses scopes haven't been in the hands
of cal lab for decades makes it even more likely that
the calibration constants are not worthy of saving.

Sure, some of the values may be right on, but which
are those? Which are wrong? You really can't tell
until you calibrate the scope.

How many of the guys on this group have replaced a
vertical attenuator, vertical hybrid, trigger hybrid,
a couple of 10K precision resistors on an A5 board,
a tripler, or perhaps even an entire EHV power supply
board and never once thought about doing a calibration?

Show of hands?

-Chuck Harris

Michael A. Terrell wrote:

How many people would calibrate a scope, before verifying the scope didn't have bad caps? The S/H cap would be the least likely to fail, compared to the average lifetime of the electrolytics. Also, most of the scopes ending up in private hands haven't been in a cal lab for years or even decades so recapping the electrolytics would return it to the condition it should have been in at the last calibration. At least, anything I repaired would have been done this way.

Leakage around the S/H circuit's capacitor could be affected by contamination on the circuit board, as well. A good cleaning should always be part of testing and calibrating very high impedance circuits, as you well know. :)

I too, have worked in electronics for decades. Over five of them including at the factory on systems that were only allowed a 1.5 mV error in a system with a 0 to 5V output in a complex AGC circuit comprised of 14 Op-Amps. One of these boards was part of a kU band communications system for the International Space Station.


Michael A. Terrell

Re: Tek 2467B

tekscopegroup@...
 

Here's my optimistic view.

Imagine a scope that has not been calibrated in many years, last time was probably while it still was in its prime, and caps where up to spec, very little power supply ripple (within specs). Now move forward some years (or decades), during which the scope was ever calibrated again. This is probably the case of I would assume most recycled scopes sold on ebay, and I'll bet that its also the period during which the filter caps started to deteriorate. Wouldn't in this case recapping the power supplies, at least in theory, actually bring the scope back more towards correct calibration rather than worsening it? I understand there are many other factors to consider than the power supply caps, as it was pointed out earlier. But just for a minute and for the fun of it, lets consider this scenario only. And again, from a hobbyist perspective only.

Re: Tek 2467B

Michael A. Terrell
 

How many ever worked in a Metrology lab? How many on here ever did mission critical work, where it was damn near impossible to get the equipment back in a reasonable time, to correct any errors? Our equipment ended up in space, or places like Antarctica where it could take a year to return and repair a piece of equipment due to the transportation issues.

I agree that the old stored values are not all correct, but they are better than nothing for a casual user who can't do a full calibration.

If they need better results, then it should be sent out for a proper calibration, but after doing the usual PM.

One job while in the US Army was doing PM on hundreds of video monitors for the Helicopter Flight School at Carin Airfield, and for the Air Traffic Control Towers. Rather than wait for them to fail, they were rotated out to the shop every six months and examined for possible problems. Even back in the early '70s, we saw a lot of bad electrolytics in the equipment. It was no fun carrying those 25" steel cased monitors up the narrow circular stairs to the control room.
Still it was better than the higher risk of losing more than one monitor when our section's shop was closed. The pilot's classrooms used regular TVs, so they were someone else's problem, but there were multiple monitors scattered all around the ready rooms and towers for two channels of weather data. If our system went down, they closed the school until it was back up and running.

Michael A. Terrell

-----Original Message-----
From: Chuck Harris <cfharris@...>
Sent: Oct 15, 2018 10:08 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 2467B

How many people would simply slap a calibration sticker
on a scope and charge for the calibration?

Using yourself as the minimum standard by which all
technicians, and calibration shops, operate is rather
fallacious.

That most of theses scopes haven't been in the hands
of cal lab for decades makes it even more likely that
the calibration constants are not worthy of saving.

Sure, some of the values may be right on, but which
are those? Which are wrong? You really can't tell
until you calibrate the scope.

How many of the guys on this group have replaced a
vertical attenuator, vertical hybrid, trigger hybrid,
a couple of 10K precision resistors on an A5 board,
a tripler, or perhaps even an entire EHV power supply
board and never once thought about doing a calibration?

Show of hands?

-Chuck Harris

Michael A. Terrell wrote:
How many people would calibrate a scope, before verifying the scope didn't have bad caps? The S/H cap would be the least likely to fail, compared to the average lifetime of the electrolytics. Also, most of the scopes ending up in private hands haven't been in a cal lab for years or even decades so recapping the electrolytics would return it to the condition it should have been in at the last calibration. At least, anything I repaired would have been done this way.

Leakage around the S/H circuit's capacitor could be affected by contamination on the circuit board, as well. A good cleaning should always be part of testing and calibrating very high impedance circuits, as you well know. :)

I too, have worked in electronics for decades. Over five of them including at the factory on systems that were only allowed a 1.5 mV error in a system with a 0 to 5V output in a complex AGC circuit comprised of 14 Op-Amps. One of these boards was part of a kU band communications system for the International Space Station.

Re: Tek 2467B

Chuck Harris
 

I am certain that you already know the answer to your question,
but I will answer it never the less...

It is possible that the last time the scope was calibrated was
when it was in pristine condition, and then it went from hand to
hand, and was used like a borrowed mule, until it finally broke
down and had a capacitor failure. In that case, replacing the
capacitors *may* improve the scope back to the condition it was
in back when it was last calibrated. But most likely, it will
need new shoes, and have some burrs in its mane and tail that
need brushing out, a harness in need of a stitch or two...

But what was the condition of the scope when it was last calibrated?
What else has degraded while those capacitors were being used up?
What else has been repaired since the last calibration?
Did the guy doing the last calibration really have his heart in it?

If, and that is a big if, the scope was monitored for its accuracy
and performance regularly throughout its life, and all of its previous
repairs, abuses, whatevers, were logged and could be analyzed, then
you could probably hazard a guess as to what the effect of some
repair you do might be... But who keeps such records? Especially
when they are avoiding doing regular calibrations over long periods
of time?

All we can do is guess. My guess is at any point in time, after most
any repair, calibration would be a good idea.

But as I have said numerous times before I am biased in favor of
calibrations. I look at the world through calibration colored glasses,
because I have the equipment, keep it calibrated, and calibrating these
scopes isn't a big deal to me. It is just 2 to 4 hours of time well
spent.

-Chuck Harris

OBTW, scopes have never been a hobby for me. That also colors my view
on calibrations.


tekscopegroup@... wrote:

Here's my optimistic view.

Imagine a scope that has not been calibrated in many years, last time was probably while it still was in its prime, and caps where up to spec, very little power supply ripple (within specs). Now move forward some years (or decades), during which the scope was ever calibrated again. This is probably the case of I would assume most recycled scopes sold on ebay, and I'll bet that its also the period during which the filter caps started to deteriorate. Wouldn't in this case recapping the power supplies, at least in theory, actually bring the scope back more towards correct calibration rather than worsening it? I understand there are many other factors to consider than the power supply caps, as it was pointed out earlier. But just for a minute and for the fun of it, lets consider this scenario only. And again, from a hobbyist perspective only.

Re: Tek 2467B

Siggi
 

On Mon, 15 Oct 2018 at 11:08 Chuck Harris <cfharris@...> wrote:

All we can do is guess. My guess is at any point in time, after most
any repair, calibration would be a good idea.
Anecdotally my 2467 was "a fair bit out" after I repaired it. Sadly I
didn't think to record how far out it was, I just remember being glad of
having done the work to calibrate it.
The repair was pretty trivial, in the end a 3V zener that clamps the -1.25V
reference voltage had decided to make like a short. I don't know how long
ago that scope had last been calibrated, but I don't think the repair threw
it, I think it just drifted over time.

7834 High Voltage Board

ef804s tubes
 

Hi,

recently I acquired a non-functional 7834. After finding a bad tantalum on
the +15V on the readout board and an open zener in the -50V supply,
I was very happy that the supply came up and there was no obvious short in
the high voltage section. But, no high voltage was present. After opening
the cage, I saw, somebody had disconnected the two coax connectors
supplying the AC voltage. After reconnecting, the power supply did not come
up. I disconnected the secondaries of the high voltage 25Khz transformer
but the symptom remained, so to me it looks like a shorted transformer.
Therefore, I need a new high voltage board or transformer. If you agree
with my diagnosis, could you please help to locate a high voltage board.

--
Best regards,

Fred

Re: 7834 High Voltage Board

Craig Sawyers <c.sawyers@...>
 

What you seem to be saying is that the main power supply works fine when the coax inputs to T2010 are
not connected, but when you connect them the main supply goes into tick mode?

Is that correct?

Craig

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of ef804s tubes
Sent: 15 October 2018 15:55
To: TekScopes@groups.io
Subject: [TekScopes] 7834 High Voltage Board

Hi,

recently I acquired a non-functional 7834. After finding a bad tantalum on the +15V on the readout
board and an open zener in the -50V supply, I was very happy that the supply came up and there was
no obvious short in the high voltage section. But, no high voltage was present. After opening the
cage,
I saw, somebody had disconnected the two coax connectors supplying the AC voltage. After
reconnecting, the power supply did not come up. I disconnected the secondaries of the high voltage
25Khz transformer but the symptom remained, so to me it looks like a shorted transformer.
Therefore, I need a new high voltage board or transformer. If you agree with my diagnosis, could you
please help to locate a high voltage board.

--
Best regards,

Fred

Re: 2445A calibration

maxim.vlasov@...
 

Thank you gentlemen for all the support!

Looks like slowly but surely I make some progress. Just found that U2420D buffer is sinking 11mA. I measure at the U2420D output -8.8V but TP2421 is -1.25V. 11mA flowing through R2220 (680 Ohm). I've looked at the schematics and 11mA doesn't seem to be the current to be pulled out of TP2421. There are quite a bit of loads, but all of them in a range of dozens of KOhms. Something is pulling up -1.25V rail.
Also noticed, that the buffer was quite warm. So, I've replaced it by TL084N from TI. Same story, but the level changed by 10mV.

Have you observed this on your scopes when repairing?

One more thing - I've got -04 FW version. It seems like the last version was -09 for 2467 o-scope. I wonder whether I can run the latest FW. If so, then in the guts of the o-scope there should be a HW identification register somewhere to tell to the FW whether it's 2445/55/65 or 67, IMHO. Otherwise the code is almost the same.

Thank you,

Re: Tektronix 2467B good buy?

victor.silva
 

I'm replying to this thread because I saw some misinformation in some responses.

The 2467B, 2465B and 2445B all share the same firmware.
You need to see if you have a post B050XXX serial or pre-B050xxx serial number.
With a post-B050 s/n you will have a surface mount A5 controller and this will use a Dallas NVRAM (with lithium cell inside it).
With a pre-b050 s/n you will have a thru-hole controller and it has a separate Eagle-Pitcher battery and low power RAM.

You have probably lost your calibration.

I would not spend the money on a calibration without doing a full refurbishment of the power supply (re-cap).

Re: 2445A calibration

Chuck Harris
 

The motherboard A1 tells the control panel which scope model
it is. It has a jumper to distinguish between a 2445B and a 2455B.
It has a pass through jumper that distinguishes the 2465B and 2467B.

They are well hidden, but they show up on the upper left corner of
the ANALOG CONTROL schematic for the A5 board, B050000 and above
in the 2467B manual.

J512, pin 11 is labeled 45A-55A ID, and,
J512, pin 32 is labeled 65A-67 ID.

The ID's are deleted from the B049999 and below schematic.

On the A1 board the 45-55 jumper is called W120 (gnd or no gnd).

And J512 pin 32 gets passed through the A1 board to J191 pin 2,
which goes to the CRT power supply board, where it is grounded
for a 2467B, and left open for a 2465B.

-Chuck Harris


maxim.vlasov@... wrote:

Thank you gentlemen for all the support!

Looks like slowly but surely I make some progress. Just found that U2420D buffer is sinking 11mA. I measure at the U2420D output -8.8V but TP2421 is -1.25V. 11mA flowing through R2220 (680 Ohm). I've looked at the schematics and 11mA doesn't seem to be the current to be pulled out of TP2421. There are quite a bit of loads, but all of them in a range of dozens of KOhms. Something is pulling up -1.25V rail.
Also noticed, that the buffer was quite warm. So, I've replaced it by TL084N from TI. Same story, but the level changed by 10mV.

Have you observed this on your scopes when repairing?

One more thing - I've got -04 FW version. It seems like the last version was -09 for 2467 o-scope. I wonder whether I can run the latest FW. If so, then in the guts of the o-scope there should be a HW identification register somewhere to tell to the FW whether it's 2445/55/65 or 67, IMHO. Otherwise the code is almost the same.

Thank you,

Re: Tek 2467B

Robert Calk Jr.
 

Thanks guys,

First I would like to apologize to rpoz28cam. I did not mean to hijack your thread. I didn't realize that my comment would turn into such a discussion.

Maybe I will be ok because the ESR of the primary filter caps are great. They are just a little out of capacitance and seem to be trying to open up around the leads. I will try to upload some photos but this will be my first attempt since I am new to the group. The Marcon e-caps still look beautiful. But there are a couple of the plain jane looking e-caps that are starting to bulge a tad on top, so I thought it best to replace all of them with probably Nichicon caps, except maybe for the Marcon's. I don't see any leakage anywhere.

Before I opened the scope this time, I went to the Service Manual and did the CRT calibration tests. The scope was spot on in every test so much so that I thought I was doing something wrong. So I redid the tests and it was spot on again.

The boards in this scope look pristine. A couple of years ago when I opened it up the first time to change the memory back-up battery, I could not find one speck of dust anywhere or any evidence that anyone had ever opened the scope up before. The scope looked like it came from a Museum. Of course I only had to pull the one board and it wasn't that big of a deal.

I don't think that there was much of a ripple problem. So I'll change all the caps and put the scope back together and see what the calibration looks like. I think it will be just fine.

Thanks guys. I really appreciate all of the help and info that you have all provided. Thanks!

Robert