Boss CS-3 making a 'fuzzy' noise

[elvis80]

I've just got back into playing the guitar after a few years in the wilderness. I (literally) dusted off my pedal board and all but one pedal worked. When switched on, the Boss CS-3 compressor gives off a fuzzy / distorted sound. The compression still works, but it sounds awful. The noise doesn't seem to change if I give the pedal a bit of a shake (so I'm assuming it's not a loose connection). Any ideas chaps? I've tested it with a variety of equipment so it's definitely not the pedals or cables.
Thanks in advance

[Mark Hammer]

Is the fuzziness unique to any point in a "note lifespan"? I.E., more likely at the fadeout than at the start.

Is the power sufficient? Is there a "compromised" battery in there?

[elvis80]

Is the fuzziness unique to any point in a "note lifespan"? I.E., more likely at the fadeout than at the start.

Is the power sufficient? Is there a "compromised" battery in there?

The fuzziness appears at all times. It is more pronounced when playing a note but not at any time within the note lifespan particularly. I'm using a proper Boss 9v power supply and it works perfectly with my other Boss pedals; noise free.

Thanks

[Mark Hammer]

Okay. The FETs used for switching are not always able to handle all manner of signals passing through them. Any possibility you are feeding the pedal too hot a signal?

One possible test is to simply jumper the FET that would normally be electronically enabled by the switching circuitry. From the information I have, this would be the K30A transistor labelled Q4. Run a temporary jumper between the wiper (middle lug) of the Level pot and the .047uf cap that the FET normally connects to. This will put the pedal permanently "on". If the sound coming through is clean when the FET is effectively out of circuit, then I think you have our culprit.