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HP 3325A gen synth AMPL CAL 2 self test fail

 

Bonjour it was fine, a few years ago, now on startup and self test, Sq wave AMP CAL 2 fails, but the sq wave and other outputs are in spec.

Full printed HP service manual does not give any clew.

All functions work fine. Why the error and CAL, self test fail messages?

Many thanks

Jon
 

Hi,

The unit is definitely not happy about something. The service manual contains quite detailed troubleshooting information. Unfortunately the 3325A does not really give additional information on what failed, the 3325B is better in this respect.
However, you say that it was not used for a long time. I had one 3325A once, which failed the amp cal, and it turned out that it simply drifted out of spec. I performed the adjustment procedure described in the service manual and everything was fine after that. Other than this there is a known problem with the flat ribbon cables connecting the boards, especially in the A version they were really crappy. I had all sorts of problems manifesting themselves in various calibration failures. Eventually I replaced them with pin headers, that solved it. So check those cables for proper seating.

Szabolcs


Froggie the Gremlin <jonpaul@...> ezt ¨ªrta (id?pont: 2024. febr. 19., H, 14:39):

Bonjour it was fine, a few years ago, now on startup and self test, Sq wave AMP CAL 2 fails, but the sq wave and other outputs are in spec.?

Full printed HP service manual does not give any clew.

All functions work fine.? Why the error and CAL, self test fail messages?

Many thanks

Jon
 

Dear Szabolcs, nice to have your notes, are you in Hungary?

I am sure it's as you said just components drift.

I am aware of the poor ribbon connectors, have used contact cleaner and r¨¦plugged them all.

So, the error in amplitude is just a few %. Agree on performing the CAL AMPL proceedure.

Will report result soon

Jon
 

I have just repaired my 3325B with a similar issue.
The ribbon connectors may be worth visiting again but not with contact cleaner but a close check on the solder joints into the pcb?
I could temporarily fix the startup fault by 'jiggling' the ribbon cable but next day the fault was back.
I removed the board and looking underneath I found grey circles of crystalline solder around many of the pins.
I re-soldered all the pins and the fault was fixed.
Not sure if the same cabling is used in the 3325A version but if it is, then check it out.
Dave
 

I have two 3325As on the bench, both with the same problem. Thanks for sharing your experience, Dave, it will definitely help us sort them out.

Pete?

On Tue, 20 Feb 2024 at 08:47, Dave B <davebullockmbe@...> wrote:
I have just repaired my 3325B with a similar issue.
The ribbon connectors may be worth visiting again but not with contact cleaner but a close check on the solder joints into the pcb?
I could temporarily fix the startup fault by 'jiggling' the ribbon cable but next day the fault was back.
I removed the board and looking underneath I found grey circles of crystalline solder around many of the pins.
I re-soldered all the pins and the fault was fixed.
Not sure if the same cabling is used in the 3325A version but if it is, then check it out.
Dave

 

Hi Jon,

Yes, I'm in Hungary, do you need anything from here? :-)
About the ribbon cables, I'm not sure if contact cleaner is sufficient. I am talking about the flat cables that slide in the socket. I think HP later replaced them with normal IDC connectors.
Although I saw oxidation on the cable ends, it seemed to me that the socket can become loose and not grab the cable enough. I had a lot of problems, so finally what I did was to remove the sockets and replace them with a simple pin header socket. The cables could also have been replaced with normal ribbon cables, but It was simple to just solder a pin header to the cable ends. Since the flat cable is somewhat rigid, it basically meant the soldering could be done very quickly and easily, definitely much less work than stripping and attaching normal ribbon cable.
Of course, the most elegant solution would be to use idc connectors, but I had all these in components in my drawer. Once I did all the tedious work of removing the old sockets and doing the soldering, I had zero problems later. I can't show you pictures, because I sold my 3325A when I got a fully optioned B version, but never heard any complaint from the buyer, so I guess it worked.?

Szabolcs

Froggie the Gremlin <jonpaul@...> ezt ¨ªrta (id?pont: 2024. febr. 19., H, 18:11):

Dear Szabolcs, nice to have your notes, are you in Hungary?

I am sure it's as you said just components drift.

?I am aware of the poor ribbon connectors, have used contact cleaner and r¨¦plugged them all.

So,? the? error in amplitude is just a few %. Agree on performing the CAL AMPL proceedure.

Will report result soon

Jon
 

Szabolcs many thanks , I have old friend from Budapest back to 1981. Redl held microwave chair at Tech U of Budapest.


1/ Agree the old flat cable connectors are unreliable, but I have not had any issues in the 3325A.


2/ RE AMPL CAL FAIL, culled a box of 50 Ohm BNC terms to find one exactly 50 Ohms.

On my HP 6.5 dig DVM, 34465A, with 3325A set for 10V out DVM with 50 Ohm term is reading ~ 9.85 V

I wonder the tolerance on the AMPL CAL to show FAIL?

3/ Need to find time to perform the simple AMPL CAL procedure.

Have a great day,

Jon
 

I believe that the problem with the flat cables is that the IDC connections themselves become flaky.? While you can attempt to re-crimp the connections, I just use 6" ribbon cable jumpers, pre-terminated on each end, as a replacement.? They are available for practically nothing on Amazon or ePay and have worked extremely well for me.? Also, the ribbon cable connecting the front panel to the motherboard often becomes loose so it is a good idea to make sure it is completely plugged in tightly on both ends if you have the case open.

Hal
 

Hi,

Nice, I graduated at that university, though a bit later.
The amplitude calibration is detailed in the manual, of course. One thing that I have seen people making mistakes is that the output of the DAC is derived from the power supply. So if you set the power supply to the precise 15V, then in the subsequent calibration step you may need to reset it outside of the nominal range, which could be confusing.But it is of course noted in the manual. But this also means that if the power supply drifted then it impacts very much the output amplitude. I don't quite remember what is used as a reference when the self test checks the calibration.
Anyway it is a quite fascinating circuit, everything is done with currents, so it is not trivial to measure things easily and there are several versions of it, so if you need to dig into the circuit then be prepared to use the service manual and check the changes. I spent some sleepless nights on my 3325A to figure out why there is an amplitude dependent asymmetrical offset. Finally I found out that a 8.2V zener diode somehow became a 3V zener. But it was a nice learning opportunity just to figure out how the output amplifier and offset stage works.?

Szabolcs


Froggie the Gremlin <jonpaul@...> ezt ¨ªrta (id?pont: 2024. febr. 20., K, 15:07):

?Szabolcs many thanks , I? have old friend from Budapest back to 1981. Redl held microwave chair at Tech U of Budapest.


1/ Agree the? old flat cable connectors are unreliable, but I have not had any issues in the 3325A.


2/ RE AMPL CAL FAIL,? ? culled a box of 50 Ohm BNC terms to find one exactly 50 Ohms.

On my HP 6.5 dig DVM, 34465A,? with 3325A set for? 10V out DVM with 50 Ohm term is? reading ~ 9.85 V?

I wonder the tolerance on the AMPL CAL to show FAIL?

3/ Need to find time to perform the simple AMPL CAL procedure.

Have a great day,

Jon





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