Studer 962 oscillating

[JRJR]

Hey guys!
I've encountered a very strange problem with a Studer 962 mixing desk that I have no clue how to solve.
Switching the desk on it serves a thumping, clicking, stuttering sound. Like fast drum hits almost.
When one of the master channels is unplugged it stops immediately. It does not matter which one.
When I put the cassette back in it takes 1-2 seconds then it comes back.
With plugging in some jacks into the inserts the frequency can be modulated and changed.
The thing is: I don't want a synthesizer - I want my mixing console back!
What could cause this and what would be a solution to this?
I was thinking about adding caps to the voltage rails to calm down the currents but I'm not sure.
Your help is very much appreciated!

 

[pucho812]

Fault finding in a console can be a tedious task especially if the issue is intermittent. In this case the issue only happens when both master channels are in play, connected. That would lead me to look for a problem that is common to both, which would be power. But that is just a guess

 

[Brian Roth]

Hopefully you have access to a DVM and an oscilloscope. Check the power rail voltages to see if they are correct and steady. If those are off, use the 'scope to see what's going on.

Bri

 

[JRJR]

Yeah it must be the power rails. I get clean signals out of all modules in all configurations - just when I add the second master section it starts to program an 80s bassline.
I'm gonna recap the PSU first, that needs to be done anyway and see what happens. Hopefully it's the leakage of the elkos causing it. If not I'm gonna dig out the oscilloscope. Thanks guys!