C-Audio SR404 hand holding for diagnosis requested

[boomi]

Hi all

My good old SR404 is loosing it. It now behaves as if the protect logic was reversed: When switching on there's a loud cracking in the speakers, and input is immediately amplified. After a fraction of a second the soft start circuit cuts in, the relay seems to oscillate shortly. 'protect' stays on until power is turned off. When turning off the power, 'protect' goes off and the amplifier works for a short while, draining the capacitors.

It seems that just the protect circuit is broken. Contradicting to this, when I tried and switched to 'bridge' mode the amplifier turned on alright and worked (there was some distortion; I'm unsure whether this was due to the amplifier or the crappy speakers).

There are two threads on this board discussing protection circuitry of the SR606. My problem is that I am unable to follow the discussion, having only rudimentary knowledge of electronics, none on amplifier circuitry. (I do know how to use multimeters and solder irons.)

Any help in diagnosing my SR404 is welcome.