Gallien Krueger MB150S Output Issue

[stereomonostereo]

Hey guys,

I'm working on a Gallien Krueger MB150S amplifier with no output. When you initially turn the amp on, you hear sound from the speaker for a split second. Tracing the signal, I'm getting sound all along the preamp to P2. The effects send and the headphone jack both have output. The effects return gives me nothing at the output. I'm thinking it's something in the output section cancelling the signal. I'm seeing an Overcurrent and Thermal shutdown on the schematic. Could that be the culprit?

Thanks!

[Jazz P Bass]

Thanks for posting the schematic.

There will Not be a signal at the FX Return jack.
The jack has a normally closed contact that passes the preamp signal.
When a plug is inserted into the FX Return, it interrupts that signal.
You could try a jumper cord from send to return to prove out the jack.

Alternatively , a signal can be inserted into the FX Return jack, thus bypassing the preamp.

Keep searching for where the signal drops out.