keeley compressor not working

[rutledj]

I have a 4 knob compressor and I'm not entirely sure it even works. I bought it off ebay. I can play sound through it with no problem. All of the controls affect the sound when they are turned but I don't really hear any compression, even with the sustain knob completely CW.

When you turn the sustain knob CCW you don't get anything out, regardless of where the level knob is set. As you turn up the sustain it gets louder. Is the correct behavior for this pedal?

Any suggestion on where to look for a problem (assuming there is one)? I replaced the IC with a new one of the same type. Doesn't look like much else there to go bad unless one of the 4 transistors are bad. It uses mps A18 transistors.

Thanks,
Rut

[petemoore]

Responding to qoote of your first paragraph...
Comps can be hard to discern: Speakers compress, amp might compress...
,,,and depending upon the type of compressor, even through a big amp after, and high output pickup before, compression can be hard to notice. Feeding an envelope filter "speaks'' of the attack/sustain ramps, making an otherwise transparent sounding compression cause the envelope filters Q to sweep quite differently than uncompressed.
Reading an advertisement for the unit probably tells that it is designed to compress hard if not even signal ducking, being a keeley 4 knob 'n all.

When you turn the sustain knob CCW you don't get anything out, regardless of where the level knob is set. As you turn up the sustain it gets louder. Is the correct behavior for this pedal?
A look at the schematic will tell whether this is normal or not.

Any suggestion on where to look for a problem (assuming there is one)? I replaced the IC with a new one of the same type. Doesn't look like much else there to go bad unless one of the 4 transistors are bad. It uses mps A18 transistors.
Better familiarity and understanding of the pedal circuits [try youtube for reviews/use/demo, any guitar sales site for 'brochure', google, search here] comes with the schematic.