Tektronix 2465B oscilloscope teardown

[med6753]

Ok in case anyone is still interested I found the issue. The unit has a bad A&B Trigger chip - 155-0239-02

Good deal! Were you able to confirm that with a replacement part?

[tazdog]

Yes, replacing the part fixed the issue  . I must say that when I was testing the scope, the low level trigger wasn't working properly. At 50mV vertical sensitivity or lower, I could get the trigger light to indicate a trigger condition but the scope display was unstable. This further led me to believe that the issue was the trigger chip.

[sekess]

Hey guys.  I'm new here.
Just came across this thread.  Excellent info.

From reading through this thread, I think it's time for me to change out my Dallas RAM.  I think I'll go with the FM16W08.  But, I have a question about sourcing an adapter pcb.  The one that I saw used here was this Aries adapter from Digikey:

https://www.digikey.com/product-detail/en/aries-electronics/28-650000-10/A320-ND/123761

This one goes for close to $19.  Does anyone have a source of a less expensive one that is still decent quality with the thin round pins?

  Thanks,
    Steve 

[boro]

Hi everybody! This is my first post and I wanted to thank you all for this great and informative thread!

I have a 2445A that lost tha calibration data due to the Keeper battery age...
I had the first warnings a few months ago, but by the time I was able to purchase a new Keeper, via a friend Down Under, because their shipping is forbidden to Italy, I got to the dreaded Test 04 fail error...
I don't need a super calibrated scope, I just use it for some basic troubleshooting and I only got a (cheap) signal generator and a (cheap) DMM.
I went through all the pages of the thread but it's still not clear what are my options at this point. Calibrating it would set me back some 150€ plus shipping. I might even think of doing so but I wondered whether once the machine underwent through all the calibrating steps, and putting back the nocal jumper, the scope would retain the data. Dumb question I know... 

Thank you all for any advice/info you'll want to provide me, it'll be much appreciated!

B.

[pquadrat]

Hi everyone,

very good thread about the 2465B Scope. I got mine some years ago from ebay, a 2465BDV, which hat some options included (01, 05, 06, 09, 10), TV triggering, CTT, Word Recognizer Probe, DVM, GPIB). It came frome a production site, a lot of opreation hours, very few on/off cycles.
Just replaced all caps in the power supply, and the Dallas chip and the already leaking electrilytics on the A5 boards. Without this thread, I would never have noticed that, thanks!
I bought a Dallas chip from china, which was an old one with reprinted date code. And then one from a local distributor, which was fresh.

Because there were no pics of a BDV in this thread ( I think), I will post some:

Next post will be about my new scope, a 2445B.

[pquadrat]

more...

[pquadrat]

Now to my new scope, a 2445B (same as a 2465B except bandwith), Serial below 050000, so it has the old-style A5 board without SMD and without the leaking caps.
It looks almost like new, has below 900h of operation, came from a broadcasting station (sfb, Sender Freies Berlin) here in Germany.  I did the bandwith "hack" on the A1 board (seems to work very close to my 2465B).

But it has a focus problem: When cold, it is extremely out of focus (and astig as well), it takes 5 to 10 minutes to get a sharp image. My other 2465BDV is perfect from the first second.

I did replace all caps in the power supply. But I am not sure if this problem was there before the re-cap, because this was one of the first things to do after getting the scope.

Any suggestions? I did check the supply voltages (J119 on Board A1), all stable from the beginning.

[med6753]

Hi everyone,

very good thread about the 2465B Scope. I got mine some years ago from ebay, a 2465BDV, which hat some options included (01, 05, 06, 09, 10), TV triggering, CTT, Word Recognizer Probe, DVM, GPIB). It came frome a production site, a lot of opreation hours, very few on/off cycles.
Just replaced all caps in the power supply, and the Dallas chip and the already leaking electrilytics on the A5 boards. Without this thread, I would never have noticed that, thanks!
I bought a Dallas chip from china, which was an old one with reprinted date code. And then one from a local distributor, which was fresh.

Because there were no pics of a BDV in this thread ( I think), I will post some:

Next post will be about my new scope, a 2445B.

Welcome to our group of Tek 24XX users. I'm glad you found all the information you needed to get yours up and working, especially in reference to the specific issues with the SMD A5 board. I have an older 2465 DMS which has the same features as yours but has the older pin thru hole A5 board. I'm sure you found getting the scope apart to re-cap the power supply very challenging as I did. All those option boards have to come out and then reassembly can be frustrating.

[tautech]

Any suggestions? I did check the supply voltages (J119 on Board A1), all stable from the beginning.

Focus (excuse the pun) investigations on componentry in the EHT supply for the CRT, that's where these sorts of problems are normally found IME.

[med6753]

Now to my new scope, a 2445B (same as a 2465B except bandwith), Serial below 050000, so it has the old-style A5 board without SMD and without the leaking caps.
It looks almost like new, has below 900h of operation, came from a broadcasting station (sfb, Sender Freies Berlin) here in Germany.  I did the bandwith "hack" on the A1 board (seems to work very close to my 2465B).

But it has a focus problem: When cold, it is extremely out of focus (and astig as well), it takes 5 to 10 minutes to get a sharp image. My other 2465BDV is perfect from the first second.

I did replace all caps in the power supply. But I am not sure if this problem was there before the re-cap, because this was one of the first things to do after getting the scope.

Any suggestions? I did check the supply voltages (J119 on Board A1), all stable from the beginning.

Attached is a partial schematic of the 2465 focus/astig circuit. The 2445 should be similar. The first thing I would check is that -300V to Q1851 and Q1852. With the scope "cold" and power off hang your probe on that supply and see what it does as the scope powers up and warms up. Of course be VERY CAREFUL working around the high voltage supply. It can really hurt. 

[pquadrat]

Now to my new scope, a 2445B (same as a 2465B except bandwith), Serial below 050000, so it has the old-style A5 board without SMD and without the leaking caps.
It looks almost like new, has below 900h of operation, came from a broadcasting station (sfb, Sender Freies Berlin) here in Germany.  I did the bandwith "hack" on the A1 board (seems to work very close to my 2465B).

But it has a focus problem: When cold, it is extremely out of focus (and astig as well), it takes 5 to 10 minutes to get a sharp image. My other 2465BDV is perfect from the first second.

I did replace all caps in the power supply. But I am not sure if this problem was there before the re-cap, because this was one of the first things to do after getting the scope.

Any suggestions? I did check the supply voltages (J119 on Board A1), all stable from the beginning.

Attached is a partial schematic of the 2465 focus/astig circuit. The 2445 should be similar. The first thing I would check is that -300V to Q1851 and Q1852. With the scope "cold" and power off hang your probe on that supply and see what it does as the scope powers up and warms up. Of course be VERY CAREFUL working around the high voltage supply. It can really hurt. 

I checked all voltages around Q1851 and Q1852, all very stable from the beginning. -300V is stable.  Focus can also be bad if other voltages of the tube are wrong, so I have to look elsewhere.

There is a test point "74" with a warm-up voltage raising from zero to 15V (around U1890), I will try to understand what is done with this circuit.

[med6753]

Now to my new scope, a 2445B (same as a 2465B except bandwith), Serial below 050000, so it has the old-style A5 board without SMD and without the leaking caps.
It looks almost like new, has below 900h of operation, came from a broadcasting station (sfb, Sender Freies Berlin) here in Germany.  I did the bandwith "hack" on the A1 board (seems to work very close to my 2465B).

But it has a focus problem: When cold, it is extremely out of focus (and astig as well), it takes 5 to 10 minutes to get a sharp image. My other 2465BDV is perfect from the first second.

I did replace all caps in the power supply. But I am not sure if this problem was there before the re-cap, because this was one of the first things to do after getting the scope.

Any suggestions? I did check the supply voltages (J119 on Board A1), all stable from the beginning.

Attached is a partial schematic of the 2465 focus/astig circuit. The 2445 should be similar. The first thing I would check is that -300V to Q1851 and Q1852. With the scope "cold" and power off hang your probe on that supply and see what it does as the scope powers up and warms up. Of course be VERY CAREFUL working around the high voltage supply. It can really hurt. 

I checked all voltages around Q1851 and Q1852, all very stable from the beginning. -300V is stable.  Focus can also be bad if other voltages of the tube are wrong, so I have to look elsewhere.

There is a test point "74" with a warm-up voltage raising from zero to 15V (around U1890), I will try to understand what is done with this circuit.

Yep, that circuit is the grid bias to the CRT. If that's not correct it will affect the focus. Section 5-4 of the Service Manual describes the adjustments. If you have a slowly rising voltage at the output of that Op-amp concurrent with better focus I would check for leaky capacitors in that area.

[pquadrat]

Yep, that circuit is the grid bias to the CRT. If that's not correct it will affect the focus. Section 5-4 of the Service Manual describes the adjustments. If you have a slowly rising voltage at the output of that Op-amp concurrent with better focus I would check for leaky capacitors in that area.

I charged and discharged the C1990 an was able to bring the voltage at the output of the op-amp to 0v or 15V, without affecting the focus much.
Grid bias adjustment was done exactly as written in the adjustment section. I will check testpoints 72, 73 next.

I checked the Output of the High Voltage Module U1830, pin 4, which should be -900V, according to the schematics. It is only -617V.

The focus pot is near the end of the adjustment range when in focus, and I can never get it as sharp as my other 2465B.

But now I have to wait an hour or so until the bad focus is back. Cooling the HV board with cooling spray does not help, so I think it is not heat related.

[pquadrat]

Tthe Output of the High Voltage Module U1830, pin 4 is also 617V on my other 2465B, so I think 900V is an error in the schematics.

[med6753]

Thinking out loud....try swapping the HV supplies between the 2 scopes. I believe they are the same part number. I've never pulled the supply in a 24XX so I don't know how difficult it would be.

If that doesn't fix it you basically only have one thing left. The CRT itself. If it were "gassy" (loosing it's vacuum) or has low emission it could cause an extended warm up time. 

[pquadrat]

Thinking out loud....try swapping the HV supplies between the 2 scopes. I believe they are the same part number. I've never pulled the supply in a 24XX so I don't know how difficult it would be.

If that doesn't fix it you basically only have one thing left. The CRT itself. If it were "gassy" (loosing it's vacuum) or has low emission it could cause an extended warm up time.

Swapping the A9 (HV) boards did not change anything. 2465B sharp as ever, 2445B sharp 10 minutes from start. And it takes about one hour  switched-off to get it fully out of focus again.

I have never heart of a bad 2465 CRT up to now. And it is bright from the first moment.

I will check the power supply again, because I think it was not having this problem before i replaced the caps in it, or at least not so bad. I think I would have noticed that.

[med6753]

Thinking out loud....try swapping the HV supplies between the 2 scopes. I believe they are the same part number. I've never pulled the supply in a 24XX so I don't know how difficult it would be.

If that doesn't fix it you basically only have one thing left. The CRT itself. If it were "gassy" (loosing it's vacuum) or has low emission it could cause an extended warm up time.

Swapping the A9 (HV) boards did not change anything. 2465B sharp as ever, 2445B sharp 10 minutes from start. And it takes about one hour  switched-off to get it fully out of focus again.

I have never heart of a bad 2465 CRT up to now. And it is bright from the first moment.

I will check the power supply again, because I think it was not having this problem before i replaced the caps in it, or at least not so bad. I think I would have noticed that.

I've never heard of a bad 24XX CRT either, other than ones broken due to shipping damage or falling off a bench.

[MarkL]

...
I will check the power supply again, because I think it was not having this problem before i replaced the caps in it, or at least not so bad. I think I would have noticed that.

If you're not already doing so, use a scope in addition to a DMM to make sure there's nothing strange happening on any of the supplies.  (Maybe something with the +87V supply?  It supplies CRT ANODE #1 directly.)

I think your experiment with C1990 was a good idea, and also checking the ASTIG and FOCUS outputs to the CRT.  I would try monitoring ALL the voltages going into the CRT to see what (or if) anything is changing over the warm up.  And compare those to your working 2465B over a warm up.

If you get desperate enough as a last resort, there's always swapping in the good CRT for a test.  The procedure is not too bad but it does take a couple of hours.  The 14kV acceleration anode holds a charge for a LONG time (speaking from experience - Ouch! is all I have to say).

[korlatos]

Since there is no way to remove the RAM to read the contents, without losing the data, there must be a method for the scope to "restore" itself from a dead battery.

This might be possible through the GPIB interface; I do not remember.  One of the 2465 series experts will know.

I don't know about the 2565A/2467, but the EAROM in the 2456 can dumped via GPIB.  By examining the EPROMs on the GPIB board I was able to figure out the following.  It may be extensible to other models.

First, you have to enable the "special" commands:

  key 0

Then you can dump the EAROM with the following command:

  earom? <address to dump>[,<address to dump>,<...>]

This allows reading out of multiple locations in one command.  For example, to dump the first 10 addresses:

  earom? 0,1,2,3,4,5,6,7,8,9

Then the next 10:

  earom? 10,11,12,13,14,15,16,17,18,19

And so on, until address 199.  The first 100 locations are the EAROM on the main board, and the second 100 is the EAROM on the buffer board.  This is the same as in the exerciser.  The values should match.

The above commands return a line in the form (from the above example 0 to 9):

  EAR 0:84,1:1993,2:10102,3:1893,4:10091,5:1798,6:1494,7:1420,8:9608,9:1431;

The return format is <address>:<value> and everything is in decimal.  You can set an EAROM value by using the same format:

  earom <address>:<value>

Trying to write multiple values in one line didn't work for me and crashed my scope.  YMMV.

It would be interesting if someone could try this on a model other than a 2465(plain).

WARNING!!   If you want to play with any of this, be careful not to overwrite overwrite the EAROM values until you've saved them with a screen capture!  On my 2465 it DOES NOT MATTER if you have the the cal jumper set to off.  These commands are surely hidden for a reason!


If you're even braver, there's another hidden query I've discovered called "BYTE?".  It takes one argument and dumps that number of bytes from somewhere.  I can't figure out what it's dumping, and I can't make it repeat itself except after a reboot.  Eventually after several hundred bytes it causes my 2465 to reboot.  I'm mentioning it because maybe that command will be useful on other models without EAROMs.


If anyone decides to try anything, please post your results.  Obviously this needs a GPIB interface.  I haven't found any equivalent method to write EAROM/NVRAM values from the screen, although now that I found it via GPIB it makes me suspect it's possible.

I can confirm that you can dump the 2465A SRAM calibration data using GPIB and the earom? command exactly as described in MarkL's post above.

[mahwe]

Thanks for the nice teardown Photos.
sorry for my bad englisch.
I have an Tek2445B since 10 jears and i was reallly happy with it, till yesterday.
It works fine the Problem is, that my scope crt Signal Position start to jump, when i try to change the horiz./vertical Position from every Cannel(1,2,3,4) , also the mesurment (delta V delta t) jumps.
So that it makes no fun to use it .
Does annybody have had the same Problem?
First i tested the different Voltages from the Power supply but they are ok(agilent34410A tested).
If it wold be only one Funktion, than i would clean the Potys from the front pannel, but so i think it must be something on the Control /readout/Buffer Board( SMD Version 671-0965 05   P9-0247B-04 (Tektronix chip1991)).
The Signals  on the CRT seem to be ok, also the Nummbers and Letters only the Signal moved non linear up an down and the Measurment Lines.
thanks

[Satbeginner]

Check the TL074 OpAmps on the A5 board, I had several of these acting like that.

Good hunting,

Leo

[MarkL]

The analog front panel controls on the 2445B, like almost all of them in this series, are converted from analog to digital, processed by the microprocessor, and then output again as an analog signal.

Since you have multiple controls suddenly showing instability, it's probably something in common that has failed or is intermittent (including connectors).

Before digging into the control board, I would first take a look at Exerciser routine 01.  This utility displays the reading on all the front panel switches and pots in hexadecimal.  Examine the readout values of the pots that are misbehaving to see if they're stable.  This will at least divide your problem into either an input issue or an output issue.  How to access the Exerciser is described in the service manual in the "Maintenance" section.

Of possible interest are also those microprocessor controlled pots which are *not* showing instability.  That could help you narrow down what *is* working.

It might also help if you could post a short video demonstrating the problem.

[mahwe]

First thanks for your help here a small Video

https://youtu.be/MUbJ79MrbwM

the next days i will test the scope

[tazdog]

All, just a tip for anyone working on the A5 board due to capacitor leakage, don't forget to check R2010 20K trim pot. Mine was reading close to 30K so that's a big difference!!! They are easy to get from DigiKey.

[MarkL]

First thanks for your help here a small Video
...
the next days i will test the scope

Thanks, that was a great video of the problem.  It wasn't too clear because your hand was blocking the control, but it looks like the Intensity control is also affected.  That would be consistent with the issue on the other controls.

I think running the exerciser 01 as previously described would be a good next step.


In many of parts of your video you can see the output DAC stepping towards a final and stable value.  At the moment that makes me think it could be an input issue.  Running the exerciser 01 will say for sure.

The input "ADC" is actually comprised of a DAC, a comparator, and some analog MUXes to select which pot to read.  How this operates is in the Theory section under "Front-Panel Scanning and Analog Controls", and specifically "Pot Scanning".  I'd suggest reading that section if you haven't already done so.

Also note that to make troubleshooting more complicated, they use the same DAC for the output as well, which feeds an array of sample and hold circuits.

Do you have the GPIB option on this scope?  It appears you don't, given the lack of GPIB LEDs above the screen, but I want to make sure.  The GPIB interface on some scopes in this family have separate ADC/DAC circuitry that intercepts some of the analog controls, but I don't know for sure on the 2445B.

Which brings me to...  I can't find a schematic specifically for the 2445B.  If you (or anyone) knows of one, please post a link.  There are plenty of 2445B service manuals out there, but for some reason the schematic section has been omitted from all that I could find.