Ivan Barberis wrote in message
...

Hello!
I have to repair an old Cabotron amplifier.
The amp is a common class A-B, with MJ15015 e MJ15016 power transistors.
I have the output stuck to negative rail: checked all the transistor
searching for an "opened" one, every transistor is ok (also in the driver
part).
What may cause this kind of fault? Fuses are not blown.
Thanks a lot for the answers!
Ivan.

Does it have a preamp section ? if so break it at that point and check for
any DC offset , perhaps from failed opamp in the preamp