Rockford 400a4 problems

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Hello everyone, im the n00b here! I searched and was sent here from DIY mobile audio forums. To make it short, i bought a Rockford 400a4 amplifier used and it is having some problems. It's near mint in physical condition and the board inside appears totally clean. Two of the 4 channels are very dirty, noisy, and just plain broken sounding. This really makes the amp un-usable. Im familiar with working on electronics but not with amplifiers. I searched the net and found a couple other people saying they have had similiar problems with thier 400a4 amps. Someone said, "Dr Fosgate" would help me here... ANyone have a good starting place?
 
Do you have access to an oscilloscope?

Are any of the 8-legged op-amps getting hotter than the others?

With no RCAs plugged into the amp, what is the resistance between the shields of the front and rear inputs?

Is the distortion affected by the position of the switches or the potentiometers?

I don't have the schematic for this amp. If you get one from Rockford, it will make troubleshooting easier.
 
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