HP3312A function generator repair

[tom.holzwurm]

Hi guys,
I'm currently working at the repair of one of the famous HP3312A function generators. I got it as a spare part sale, but it's a condition, which hopefully allows me to get it up and running again.
I've two questions:
Is it worth the effort to replace the tantalum capacitors preventively and if, whats the better replacement: 35V tantalum caps or low ESR caps ?
The manual copies which can be found in the web are all the same crappy and very hard to read pdf-files. Is there a more readable version or is there the chance to purchase a paper manual ?
Thanks in advance for your replies
Regards
Thomas

[wn1fju]

Artek Manuals has a very nice readable copy of the 3312A service manual ($7.50 USD for a downloadable pdf).  But be aware that there are several later variants of the boards in the 3312A and the manual may be for an earlier version.  Better to see what board versions you have and check with Artek first (there was a recent eevBlog post where a person needed, and couldn't find, a later manual).

I wouldn't bother with a preemptive replacement of tantalums.  I might consider that for electrolytic capacitors, but only if one or more were showing the warning signs: bulging, leaking electrolyte, etc.  With tantalums, I just wait for them to pop, clean up any mess with alcohol, and then drop a new tantalum in there.  It doesn't happen all that often.

[precaud]

Great little generator. Make sure the manual covers the serial number of your unit. The later units had a major redo of the A2 board.

I would clean all switches and molex connectors first. Twice on mine I have spent hours chasing issues that ended up being intermittent contacts.

[tom.holzwurm]

Hi,
a big thank you for your valuable hints, espacially the manual. In the meantime I got the pdf from Artek, which is a much much better high-res scan than the omnipresent but partly illegible version from Agilent.
Well invested small change ! In the meantime after a good soak in contact cleaner the basic functions were working.
I had a 50Hz rectangular noise at the mains output, which persisted even at power off. Solution: cleaning and tightening the screws of chassis parts did the job, obviously improper ground joints.
The only open issue is the dial for the frequency, it's range is far too big and it's nearly impossible to adjust the real frequency output values according to the dial.
So I think of replacing it by a Dial Button with a 10 turns precision potentiometer.
Regards Thomas

[precaud]

after a good soak in contact cleaner the basic functions were working.

So typical! Lots of DC being bussed around via those switches and connectors. Fortunately there are little slots in the top of the swiches perfect for squirting some IPA into... and vac'ing out after working the switch a bit.

The only open issue is the dial for the frequency, it's range is far too big and it's nearly impossible to adjust the real frequency output values according to the dial.

Also typical for an analog VCO. Hard to get an exact frequency without drift. Have to go digitally-generated for that.

[petieken]

I also have a 3312A that I bought a few years ago. I've had to open it up 2 times to replace a shorted tantalum. Since a few months ago, it's dead again, the 3rd time now. I haven't had the time yet to open it up and inspect what's wrong. If it's a shorted tantalum again, I'll replace them all this time.

[tom.holzwurm]

Have to go digitally-generated for that

basically yes, but as I have an AWG in my DSO, I use the HP3312 for fast probing, where a potentiometer and simple push buttons are much faster than entering values by a virtual keyboard on a touch screen.