PSU troubleshooting questions

[Family Hoof]

I have a power supply for my Soundcraft 200 console (not 200B) circa 1985 which is acting up. The phantom supply is fine (comes from a separate tap on the TX, has its own circuit), but the +/- 17V is off. The plus side measures 18V and the minus side is -17.4. Almost all of the push buttons on this console make a loud pop when pressed, and I'm assuming this is from DC offset in the audio path (because of the difference between the two supply voltages?). Guess they're non-shorting. Also, I believe the VU meters are reading quite a bit of DC (pinned in the red as soon as the power is on, and my multimeter agrees) but they're f*cked anyway.

Apart from the first, largest smoothing cap following the rectifier I don't think anything else has been replaced, so I'm certain the entire thing is in desparate need of a recap. The other components seem alright, not that I'd really know.

The main questions are:
1) Any tips before I finish reverse engineering the thing (no schematic :sad and blow a bunch of money replacing all the wet tantalums?
2) Could old caps be solely responsible for the difference in voltages, or is there something else going on?

I'm afraid the regulator outputs are off, but they have no adjustments, are regulating to approx 0.05%, and I haven't done the math yet to know what they're supposed to be giving me. Perhaps change some of the bias resistors and my problem is solved...?

Also, is it cool to replace the wet tantalums with solid tantalum or even some high quality aluminum electros?

Thanks!,
Jens

 

[gyraf]

Voltage difference between the two power rails should NOT whatsoever result in DC in your signal path.

remember, that everything refers to ground, (I hope) not to the supply lines.

And most opamps has huge psurr at DC...

Your DC in signal circuits is probably due to leaky capacitors, not to the psu.

Jakob E.

 

[Family Hoof]

Thank you, Jakob. Well said. Of course everything is referenced to ground! That's how I measured it! It's frightening how I forget such obvious concepts sometimes. Guess I will just have to start recapping the board. Thanks for your input!

-Jens