Boss CS-3 Problem

[bluetubes]

Just got a Boss CS-3 compressor for real cheap (It's not working right).  Pedal powers on and I get output.  The problem is the Sustain knob.   When Sustain is @ 0, the pedal sounds normal but turning it up clips the signal like a distortion pedal.  I opened up the pedal and it looks like a bunch of caps have been swapped out.  All the resistors look like stock values.  Checked over the bottom of the board and it don't look like anything is shorted either.

Any ideas on what it could possibly be?

Thanks,
BT