Tektronix 2465B oscilloscope teardown

[BravoV]

That is one hell of expensive thermometer  , considering how valuable this old gem is for that purpose.

But congrats on proofing it that its still performing very good, a temp reading using a scope. 

Thanks for sharing. 

[med6753]

That is one hell of expensive thermometer  , considering how valuable this old gem is for that purpose.

But congrats on proofing it that its still performing very good, a temp reading using a scope. 

Thanks for sharing. 

You ain't kidding. The list price for a 2465 DMS in 1985 was $8400 USD.  More than the cost of a decent car at that time!

[med6753]

As promised, more updates....


The DMM option on the 2465 DMS is calibrated as far as I can go with the equipment currently on hand. Thanks to MarkL's suggestion I used a power transformer connected secondary side to a function generator to get the 19.0V RMS@60Hz. Unfortunately the power transformer could not pass the required calibration constant of 19.0V RMS@50KHz. The best I could get out of it was about 7.0V RMS. So the ranges not done are:

500V DC
19.0V RMS 50KHz
190V RMS 60Hz
500V RMS 60Hz

So unless I can beg, borrow, or steal  a Fluke voltage calibrator at this point the DMM option is a done deal and I'm pleased with the results.

One issue left....the Buffer Board checksum error. I'm working it.

[med6753]

The last issue on this Tek 2465 DMS:

BU TEST F1 FAIL 10
Buffer Board checksum error.

If I perform the DC Balance routine as defined on the attached troubleshooting chart I get some interesting results....


Upon immediate power up the scope comes up with all tests pass.
If I leave it off for about 10 minutes or so it still powers up all tests pass.
If I leave it off for about a half hour or longer the checksum error comes back.

To my simple mind I think this is telling me that the Buffer Board EAROM is defective and after a certain time frame it is dropping data.

In the reading thru the service manual it appears that EXER 02 will read the EAROM data out of both the A5 main board as well as the Buffer Board. Beyond that I'm a little ignorant (and perhaps a little fear of “fail”) as to what I can do with it. I have no experience in dealing with these types of circuits. And I'm not sure if I want to go thru the expense and learning curve to put together an ROM writer and write a new chip. Especially since it appears that this checksum error has no affect on other functions of the scope other than being an annoyance upon power up. So I'm tempted to leave it until it's a total crap out. Which may or may not ever happen. What say the group? Fix it or leave it? I'm open to suggestions.

So in summary this 2465 DMS has been an adventure since getting it (free) last year. Repaired or calibrated:

Noisy fan fixed.
Counter/Trigger option calibration power up fail fixed.
C/T and DMM option drift problem fixed after total recap of Inverter and Regulator boards.
DMM option fail fixed after self inflicted gun shot wound then calibrated.
2465 Mainframe all functions appear to be in spec to the limits to which I can test them.

[MarkL]

...
To my simple mind I think this is telling me that the Buffer Board EAROM is defective and after a certain time frame it is dropping data.

In the reading thru the service manual it appears that EXER 02 will read the EAROM data out of both the A5 main board as well as the Buffer Board. Beyond that I'm a little ignorant (and perhaps a little fear of “fail”) as to what I can do with it. I have no experience in dealing with these types of circuits. And I'm not sure if I want to go thru the expense and learning curve to put together an ROM writer and write a new chip. Especially since it appears that this checksum error has no affect on other functions of the scope other than being an annoyance upon power up. So I'm tempted to leave it until it's a total crap out. Which may or may not ever happen. What say the group? Fix it or leave it? I'm open to suggestions.
...

I also had an intermittent EAROM, but mine was on the main board.  The scope would sometimes power up with a checksum error.  I don't recall if it was dependent on how long it was off, but it could have been the same issue since data in the EAROM was being written when front panel settings were changed.

Properly done the EAROM should have been replaced, but I was able to change the supply voltage slightly and I got it to work without failure:

  https://www.eevblog.com/forum/testgear/tektronix-2445-2465-cal-settings-earom-er1400/msg927144/#msg927144

It may be a long shot, but easy to try.  The supply for the buffer board EAROM (signal OEA35) is connected to the one on the main board, so it's the same zener.

EXER02 is harmless.  You can use it to make a backup copy of the contents in both EAROMs.  Getting the data back in there, however, is another matter.  It would have been nice for them to provide a "write" option in the diagnostics.

[tggzzz]

Looking further into the 2465B’s abilities, the scope can also function as a time domain reflectometer.   For those unfamiliar with this, the scope’s speed is fast enough to measure the transit time of signals traveling through conductors.
 
For this test, I connected a BNC T to the scope 50 ohm input at channel 1.   A 50 ohm cable connected one port of the T, to the 50 ohm output of the SG503 pulse generator. 

If you think about it you can obtain the same information using an edge (not a pulse) and without using a 50ohm termination. The waveforms will look different, but the same information is easily available.

Sub-nanosecond pulses are easy to generate. In my experience, three parallel (74LVC1G14+140ohms) will drive a 50ohm load very cleanly to half the supply voltage with a risetime of, I believe, ~650ps.

A "high" impedance input will have the advantage of a higher amplitude, and the disadvantage of a marginally longer risetime.

[med6753]

...
To my simple mind I think this is telling me that the Buffer Board EAROM is defective and after a certain time frame it is dropping data.

In the reading thru the service manual it appears that EXER 02 will read the EAROM data out of both the A5 main board as well as the Buffer Board. Beyond that I'm a little ignorant (and perhaps a little fear of “fail”) as to what I can do with it. I have no experience in dealing with these types of circuits. And I'm not sure if I want to go thru the expense and learning curve to put together an ROM writer and write a new chip. Especially since it appears that this checksum error has no affect on other functions of the scope other than being an annoyance upon power up. So I'm tempted to leave it until it's a total crap out. Which may or may not ever happen. What say the group? Fix it or leave it? I'm open to suggestions.
...

I also had an intermittent EAROM, but mine was on the main board.  The scope would sometimes power up with a checksum error.  I don't recall if it was dependent on how long it was off, but it could have been the same issue since data in the EAROM was being written when front panel settings were changed.

Properly done the EAROM should have been replaced, but I was able to change the supply voltage slightly and I got it to work without failure:

  https://www.eevblog.com/forum/testgear/tektronix-2445-2465-cal-settings-earom-er1400/msg927144/#msg927144

It may be a long shot, but easy to try.  The supply for the buffer board EAROM (signal OEA35) is connected to the one on the main board, so it's the same zener.

EXER02 is harmless.  You can use it to make a backup copy of the contents in both EAROMs.  Getting the data back in there, however, is another matter.  It would have been nice for them to provide a "write" option in the diagnostics.

Mark, first....I want to publicly thank you for the prior assistance you've given me in getting this 2465 fully functional. It is greatly appreciated. 

2nd, I saw your post in the other thread concerning lowering the voltage to the EAROM and I did wonder if perhaps it would help with mine. So I did some checking but I found a discrepancy in what you did vs what is currently in place and perhaps your memory of what you did 20 years ago is a little fuzzy.

I looked up A5 Board VR2003 and it's currently a 7.5 V Zener. You indicated that you lowered the voltage by 2 volts by installing a 9.1 V Zener. Isn't that actually RAISING the voltage by approx 2 volts? But you are correct. That line (OEA35) does supply the EAROM's on the both the A5 Board and the Buffer Board.

[MarkL]

Mark, first....I want to publicly thank you for the prior assistance you've given me in getting this 2465 fully functional. It is greatly appreciated. 

2nd, I saw your post in the other thread concerning lowering the voltage to the EAROM and I did wonder if perhaps it would help with mine. So I did some checking but I found a discrepancy in what you did vs what is currently in place and perhaps your memory of what you did 20 years ago is a little fuzzy.

I looked up A5 Board VR2003 and it's currently a 7.5 V Zener. You indicated that you lowered the voltage by 2 volts by installing a 9.1 V Zener. Isn't that actually RAISING the voltage by approx 2 volts? But you are correct. That line (OEA35) does supply the EAROM's on the both the A5 Board and the Buffer Board.

You are most welcome!  I enjoy working on this old equipment and I'm usually looking for excuses to pop the lid off and get out the service manuals.  It's not something I get to do with more modern equipment I use on a daily basis for work.

On VR2003, note that it and CR2004 are used as a dropper from the +42V rail to supply the EAROM.  So, the end result to the EAROM is 42V - 9.1V - 0.7V = 32.2V.  The spec on the ER1400 says 35V +/- 8%, so the minimum happens to also be 32.2V.

I just verified the voltage on my EAROM (between pins 1 & 2) as 32.3V.  With the original 7.5V zener, this would be higher by 1.6V ( = 33.9V).

[med6753]

On VR2003, note that it and CR2004 are used as a dropper from the +42V rail to supply the EAROM.  So, the end result to the EAROM is 42V - 9.1V - 0.7V = 32.2V.  The spec on the ER1400 says 35V +/- 8%, so the minimum happens to also be 32.2V.

I just verified the voltage on my EAROM (between pins 1 & 2) as 32.3V.  With the original 7.5V zener, this would be higher by 1.6V ( = 33.9V).

D'OH  . You are absolutely correct. It's a dropper circuit from the +42V supply. I think I have a 9.1V Zener in my pile of parts. If not it will be on my next parts order. Gonna give it try and see what happens. 

[smgvbest]

Hello,

I have a 2467B that I have a GPIB interface for and I'm kind of stuck.   
It came with a A20 Buffer Board (i believe the correct name for it).   there are connections labeled C/D/E that I can find on the A1 board to connect to but also on the A20 is a 34pin connection that looks like it would go to the A5 Board but there is no 34 Pin connection available on the A5.   there is a 40Pin  my Serial Number is B053273.

So I take it this A20 Buffer Board is not compatible with my Serial Number.

Heres a few pics of my A1, A5 and A20 boards.

To use this GBIP board what am I looking for?   I could not find a A20 board in the service manual or in the option manual unless I'm totally blind

TIA

[smgvbest]

More of the images

[med6753]

To use this GBIP board what am I looking for?   I could not find a A20 board in the service manual or in the option manual unless I'm totally blind

TIA

I can't tell you specifically what you need to get the GPIB going but if you have the correct manuals the A20 Board is the Buffer Board. I have the 2465 options manuals and it shows it very clearly.

Artek Manuals has the 2467B Options Service Manuals on CD for $12.50 USD. If you don't already have that manual I would check it out.

Hope this helps.   

[Orange]

Hello,

I have a 2467B that I have a GPIB interface for and I'm kind of stuck.   
It came with a A20 Buffer Board (i believe the correct name for it).   there are connections labeled C/D/E that I can find on the A1 board to connect to but also on the A20 is a 34pin connection that looks like it would go to the A5 Board but there is no 34 Pin connection available on the A5.   there is a 40Pin  my Serial Number is B053273.

So I take it this A20 Buffer Board is not compatible with my Serial Number.

Heres a few pics of my A1, A5 and A20 boards.

To use this GBIP board what am I looking for?   I could not find a A20 board in the service manual or in the option manual unless I'm totally blind

TIA

You need a GPIB board as well, see PDF excerpt

[MarkL]

That 40-pin connector on A5 is J4241.

I don't have the 2467B options service manual, but on the other 2465/7 series scopes J4241 goes to the DMM option which is also a 40-pin connector.  A spot check on a bunch of signals on the 2467B J4241 connector shows they're the same as the DMM option pinout.

Without the manual I can't say for sure, but it's probably not coincidence.

That doesn't answer the basic question about your buffer board compatibility, though.

So, you obtained the buffer board and GPIB interface as an add-on?  (I.e., it didn't come with the scope?)

One seller on ebay (Qservice) has a listing for a 2467B GPIB retrofit kit:

  http://www.ebay.com/itm/381550986148

It looks like yours and is specifically for serial numbers < B50000.

So, it doesn't look too hopeful, but I agree with med6753 that obtaining the service manual is the next thing to do.

[Orange]

Hello,

I have a 2467B that I have a GPIB interface for and I'm kind of stuck.   
It came with a A20 Buffer Board (i believe the correct name for it).   there are connections labeled C/D/E that I can find on the A1 board to connect to but also on the A20 is a 34pin connection that looks like it would go to the A5 Board but there is no 34 Pin connection available on the A5.   there is a 40Pin  my Serial Number is B053273.

So I take it this A20 Buffer Board is not compatible with my Serial Number.

Heres a few pics of my A1, A5 and A20 boards.

To use this GBIP board what am I looking for?   I could not find a A20 board in the service manual or in the option manual unless I'm totally blind

TIA

Here is the interconnect diagram, it shows that there is no longer a buffer board in the 2467B (serials > 50000)

[med6753]

Hello,

I have a 2467B that I have a GPIB interface for and I'm kind of stuck.   
It came with a A20 Buffer Board (i believe the correct name for it).   there are connections labeled C/D/E that I can find on the A1 board to connect to but also on the A20 is a 34pin connection that looks like it would go to the A5 Board but there is no 34 Pin connection available on the A5.   there is a 40Pin  my Serial Number is B053273.

So I take it this A20 Buffer Board is not compatible with my Serial Number.

Heres a few pics of my A1, A5 and A20 boards.

To use this GBIP board what am I looking for?   I could not find a A20 board in the service manual or in the option manual unless I'm totally blind

TIA

Here is the interconnect diagram, it shows that there is no longer a buffer board in the 2467B (serials > 50000)

Wow! Those wiley Tek Engineers found a way to combine the Buffer functions on the A5 Board. Great for them but bad for us 30 years later when we are trying to figure out exactly what we have.   

[smgvbest]

Thank you for replying
So the Buffer/GPIB and CTT boards I have will end up on eBay for sale as they do me no good as they are not supported by my serial number.

I do have the full service manual but had trouble understanding the A20 board and relation to my serial number.   This is when I really miss hardcopy.  sometimes it's easier to just have an open manual.

[med6753]

On VR2003, note that it and CR2004 are used as a dropper from the +42V rail to supply the EAROM.  So, the end result to the EAROM is 42V - 9.1V - 0.7V = 32.2V.  The spec on the ER1400 says 35V +/- 8%, so the minimum happens to also be 32.2V.

I just verified the voltage on my EAROM (between pins 1 & 2) as 32.3V.  With the original 7.5V zener, this would be higher by 1.6V ( = 33.9V).

D'OH  . You are absolutely correct. It's a dropper circuit from the +42V supply. I think I have a 9.1V Zener in my pile of parts. If not it will be on my next parts order. Gonna give it try and see what happens. 

Today I changed VR2003 from a 7.5V zener to a 9.1V zener. Original EAROM voltage was 35.19V. After the zener change it was 33.19V. Unfortunately I still have the Buffer Board checksum error. So the mod didn't help. It's looking more and more like that chip is on it's last legs. Oh well. I'm going to leave it for now and consider this a completed project.

[MarkL]

Oh well - sorry the mod didn't work for you.  It was easy enough to be worth a try.

[jscgvnc]

Hey guys and gals,

I just got a 2465b, Serial B012202, and so far the only thing wrong is what I've buggered up. I pulled some jumpers out, thinking it was a 4-pin connector, and it's really 2 2-pin connectors. They are J902 and J903 on the High Voltage Supply and CRT drawing 8 of the service manual. I can figure out their numbering system for the pins. Is one the "bottom" or the "top". There seems to be a small arrow printed on the board for those jumper pins, does that indicate the start of the numbering?

I've attached a photo. I didn't take a picture of them before I removed them, so I don't know which way they go on, which I know is a rookie maneuver.

I really don't want to have to pry the whole board off to see if the pins are numbered on the other side. Can anyone help?

Thanks,

Josh

[guido]

There is an arrow on the board. And an arrow on the connector. They need to allign 
It looks like one of your connectors is not alligned.

[MarkL]

The arrow points to pin 1 and an arrow on the connector housing also means pin 1.   It looks to me like you have the orientation right. 

If you want to double check, pin 1 on both J902 and J903 are ground, so you can check for continuity to ground on both pin 1's (cables unplugged).

If your question is which cable is which, you'll have to trace where they go if they're not labeled on the wire.  P902 goes to a coil near the front of the CRT and P903 goes to a coil further back on the neck.

If you have anything wrong with these connectors the scope is not going to blow up, but the beam alignment will be a mess.

[jscgvnc]

MarkL,

Thanks for the info. Exactly what I was looking for.

[guido]

Looks like the connector/wire was replaced. Not the usuall style with the arrow. Got me on the wrong track.
Google usually is your friend. First hit with 2465b high voltage supply in pictures:



On this forum 

Note i said usually. A two pin connector to the pcb on the HV supply in the 7603 has been swapped between revisions. Including the cable (from cross wired to straight or vzv). If you do not swap the cable and pcb at the same time it doesn't work if you have two versions of the board/cable.

[BravoV]

Just realized that I still have the close-up photo on those J902 and J903 connectors orientation, and it's arrow (or pin 1) markings, put here as a reference for future owners that may experience the same problem again.