Moog Music Forum

I had a bad 12v short in my system ...all the other modules seem fine but my 904a is dead. I'm assuming it's the short that caused the problem as it was fine up to then.

I'm wondering where to start looking...I guess it must be a blown transistor ? as I cannot see any component damage or track / problems .

The unit is totally dead ...nothing at all from it not even a click.

Any suggestions where to start looking ? I'm loathe to replace any transistors for test as their all matched.

Power supply all ok ..that's not the problem

This is where guessing ends and logical diagnostics start.

If you have an oscilloscope and a signal generator (don't want to damage a VCO), route a signal to the input jack and trace it from there on the scope.

Troubleshooting with a failure of this kind is not guesswork. It is tracing from input to output, as well as verifying power rails on key components.

Thanks ...

I'm hoping the victims are Q17 Q 21 as they look like there in the front line for incoming fire.

Turned out to be a dry joint and extremely bad coincidence ....why am I so surprised ?