Date   
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

Re: 2445A calibration

Siggi
 

On Mon, 15 Oct 2018 at 15:41 <maxim.vlasov@...> wrote:

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.
I don't know whether that's unreasonable, but -8.8V out of the op-amp is
well within its control range. A TL074 will go to +12/-12V minimum on a
+15/-15V supply so I wouldn't focus there too much. If you look at the
power distribution diagram <11>(?), you'll see U700/U850/U900 get -1.25V
bias, so 11mA is probably reasonable.


Have you observed this on your scopes when repairing?
Sadly I haven't measured this - if you're stuck, I can pop the case on my
2467 this weekend and check it. Offhand, I don't think 11mA is unreasonable
however.


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.
I updated my firmware from -06 to -09 without incident. Didn't need
re-calibration that I noticed.

Re: Tek 2467B

Robert Calk Jr.
 

Hi guys,

Here are some photos. I hope that this works!

https://groups.io/g/TekScopes/album?id=75892

Robert

Re: 2445A calibration

maxim.vlasov@...
 

Siggi, Chuck, thank you for your answers,

I'll upgrade the firmware to -09. Also, hope that the calibration procedure will be more forgiving (maybe)....

Also will see what is consuming 11mA. After checking the TL072/082 and LF347N datasheets, found in LF347N the maximum voltage swing vs sink/source current rating, which is -/+12V under -/+10mA. So the operating range is close to its limit but not marginal yet.
Have to check C731 220uF capacitor on A1.
Well, I've made a small LTSpice simulation (see the schematics below) to check the DC operating point and find the currents and voltages:
https://groups.io/g/TekScopes/photo/74577/0?p=Name,,,20,1,0,0

It's very unfortunate, but it seems like everything is well in spec, so I've changed the U2420 for no reason.. Siggi, thanks a lot for offering the help in opening your scope, but it looks like everything is nominal and designed to be like this (arghhh)...
-1.25V reference and +1.36 runs through A1 and also the front board. All the pots are connected to these two rails. This circuit also includes the hold-off, SWEEP A/B ICs and even the attenuator temperature controls (every single thing measured back by ADC runs off the DAC 1mA REF. Logical, but scattered and fragile).

What I found really weird on the running oscilloscope is the difference between the A5 ground and A1 ground potential is about 0.3mV. 300uV! Also same gradient found on A5, going from 0 to about 0.3mV as measuring between ground traces on the board.

If someone have connected the o-scope to HV or the life AC and got the frontend busted, I could only assume that the ground could get compromised on A1 (somewhere between the BNC probe ground and the AC plug ground).

When you have repaired the o-scopes have you found a weak point of some sort, which can be damaged by the excessive current between BNC and the power socket GND?

Thank you,

Re: 2445A calibration

Chuck Harris
 

The BNC goes directly to chassis ground, so, your answer
is no. There is no weak point between the BNC and the
power line bond wire. Working on telephone station equipment,
I occasionally got caught by the grounding conventions, and
once burned up a probe ground wire on a 2465 without issue.

Have you solved the problem of your cursor vs the 1st and
11th graticule line yet? If not, you are still playing in
the wrong ball park. You cannot pass CAL01 and CAL02 if you
cannot get the cursor and the graticule to match each other.

The cursor is how the calibration routines know how wide the
spacing between the graticule lines is.

Also, it sounds a little to me like you don't understand that
Tek used the opamp as the "pass transistor" for the -1.25 and
+1.36 reference power supplies.

-Chuck Harris

maxim.vlasov@... wrote:

Siggi, Chuck, thank you for your answers,

I'll upgrade the firmware to -09. Also, hope that the calibration procedure will be more forgiving (maybe)....

Also will see what is consuming 11mA. After checking the TL072/082 and LF347N datasheets, found in LF347N the maximum voltage swing vs sink/source current rating, which is -/+12V under -/+10mA. So the operating range is close to its limit but not marginal yet.
Have to check C731 220uF capacitor on A1.
Well, I've made a small LTSpice simulation (see the schematics below) to check the DC operating point and find the currents and voltages:
https://groups.io/g/TekScopes/photo/74577/0?p=Name,,,20,1,0,0

It's very unfortunate, but it seems like everything is well in spec, so I've changed the U2420 for no reason.. Siggi, thanks a lot for offering the help in opening your scope, but it looks like everything is nominal and designed to be like this (arghhh)...
-1.25V reference and +1.36 runs through A1 and also the front board. All the pots are connected to these two rails. This circuit also includes the hold-off, SWEEP A/B ICs and even the attenuator temperature controls (every single thing measured back by ADC runs off the DAC 1mA REF. Logical, but scattered and fragile).

What I found really weird on the running oscilloscope is the difference between the A5 ground and A1 ground potential is about 0.3mV. 300uV! Also same gradient found on A5, going from 0 to about 0.3mV as measuring between ground traces on the board.

If someone have connected the o-scope to HV or the life AC and got the frontend busted, I could only assume that the ground could get compromised on A1 (somewhere between the BNC probe ground and the AC plug ground).

When you have repaired the o-scopes have you found a weak point of some sort, which can be damaged by the excessive current between BNC and the power socket GND?

Thank you,

Re: 7834 High Voltage Board

ef804s tubes
 

Hi Craig,
that's correct.

Fred

I still have one Mesh Filter for a 475 Scope left.

 

I found one more 4 5/8" (11.7475cm) x 3 7/8" (9.8425cm) mesh filters for the
475 to reduce glare and improve the contrast of your CRT.

There is no charge for the mesh.

The only charge is $15.00 to cover the postage, packaging, and transport to
the post office.



If you can use it please contact me directly off list at dennis at ridesoft
dot com and include your address.



Dennis Tillman W7PF



Thanks to:

Fred Schumacher for explaining what they are used for and which scope they
fit.

Lop Pol for confirming they are not for the 453 or 454

Renée for suggesting which scope they are for

Re: 2445A calibration

maxim.vlasov@...
 

On Mon, Oct 15, 2018 at 09:29 PM, Chuck Harris wrote:


Also, it sounds a little to me like you don't understand that
Tek used the opamp as the "pass transistor" for the -1.25 and
+1.36 reference power supplies.
Thank you Chuck, but now I understand in every little detail how the reference is generated and distributed all across the o-scope including the programmatic values and the expected convergence DC point after finding the DAC code and running the smal simulation.

I had to give the thorough test and find the explanation to whatever was discovered. IMHO, the problem is related to the operation or the calibration of the ADC/DAC since it fails one of automated routines. Now since the hypothesis about the bad reference distribution is dead, then I'll go with the raster step. If the raster step is OK, then then I had to pass the 1st and 11th graticules after the DAC ref current calibration. Otherwise I'll have to go back to the multichannel DAC/ADC and continue checking the sample&hold caps, muxers and the rest.

I'm advancing slowly (have not more than 40 mins per day), so please be patient with me.

Thank you,

Maxim

Re: 7834 High Voltage Board

Mark Wendt
 

On 10/16/18 00:50, ef804s tubes wrote:
Hi Craig,
that's correct.

Fred

What's correct?  It helps us follow the conversation if you quote the passage you are replying to.  There are also multiple Craig's on the list, any of which may have replied before to this thread. I've quoted your message for example.  Now folks know who I'm replying to, and why I'm replying.  Now there is context to my reply.


Mark

Re: 7834 High Voltage Board

Colin Herbert
 

While I agree that quoting text does make stuff a lot clearer, doesn't the message title help with following the conversation, too? I am a sad person who doesn't delete any of these messages from Tekscopes - I find it easier to follow the context that way.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Mark Wendt
Sent: 16 October 2018 13:41
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7834 High Voltage Board

On 10/16/18 00:50, ef804s tubes wrote:
Hi Craig,
that's correct.

Fred

What's correct? It helps us follow the conversation if you quote the
passage you are replying to. There are also multiple Craig's on the
list, any of which may have replied before to this thread. I've quoted
your message for example. Now folks know who I'm replying to, and why
I'm replying. Now there is context to my reply.


Mark