SVT -4 Pro distorted output on both amplifiers

[diydidi]

Hi All.
I have this amp for repair. Fx send out gives good, clear signal. The power amplifiers are both giving a distorted signal. Looking at the schematic of the power amps, I get clean signal up until IC1. IC1 pins 1 & 7 are both distorted.
NOW, I can't seem to figure out exactly the arrangement and workings of the circuitry surrounding IC1. Anyone?
My question however is: Can a faulty mosfet in the output stage, or faulty driver transistors cause me to see a distorted waveform on the output pins of IC1??

[Steve Conner]

Yes, IC1 is part of a feedback loop along with the driver and output stages. If there's a problem with any stage, you'll see distortion at every stage as the feedback tries to compensate for the problem.

Given that both channels are showing a problem, the first thing to do is check the things common to both channels. Supply rails?

[diydidi]

Hi Steve.
Thanx for your reply.
So what you're sayin is that the probability of the culprit being IC1, is vey low. Correct?

[Steve Conner]

No, I said that you can't tell which part of the loop is causing the problem from a casual inspection. Could be IC1, could be something else.

[Enzo]

Steve suggested the supply rails. Are BOTH low voltage power supplies up to voltage and clean? For that matter are BOTH high voltage power supplies up to voltage and clean? Nothing works if its power supply isn't right.

[diydidi]

Will check supply rails today