JCM 2000 TSL 122 FX Loop Buzz

[EVHalen]

The FX loop in my JCM 2000 TSL 122 combo has been a nightmare for me. I just recently discovered that I had the loop level switch in the wrong position, which was causing a volume and tone drop (I now keep it pushed IN instead of OUT, as this works best with my floor pedals), and I now have the FX Mix on 10 to turn the loop into a series loop, but my problems still continue.

I now have an ugly sounding 60hz buzz as a result of keeping the level switch pushed IN. Is there a way to simply have a well-functioning loop without having to choose the lesser of two evils? I want neither a tone/volume drop OR a 60hz buzz. I've already tried taking a patch cable and plugging it straight from the send to the return of my loop: same result. But obviously this test wouldn't have anything to do with the problem anyway, since the buzz is nonexistent with the level switch OUT. Anybody know what to do? Thanks in advance!

[DrGonz78]

Tell us what pedals are connected to the loop...??? We need to know what you are dealing with as to figure this out. Also, I would go through the loop with each pedal one at a time and see which pedals might be causing trouble(hum).

Edit: I read this question wrong sorry... ignore...

[nickb]

Does this happen on both A and B loops?

There should not be any change in level when you operate the level switch as when it reduces the level to to the pedal it adds gain to the the signal back to exactly compensate. Thus it just changes the drive level to the pedals. IN is best for pedals that were intended for use between guitar and amp, OUT is best for pro rack type FX.

A very common reason for failures are the connectors used internally. There is one that is used for the FX loop. I might be worthwhile taking it one on and off a few times to clean the contacts.

Edit: "E V Halen", very funny.

[g1]

As nickb mentioned, there should be no level difference when changing the switch position. Try this: patch cord from loop A send to return, fx mix set to 10. While playing is there a volume change when you change the switch position? Now try the same patch cord thing with loop B, playing through the crunch or od channel. Any change in the volume when you change the loop B switch?
If you are lucky, it could just be an oxidized/dirty contact at one of the switches or jacks, give them some exercise, plug in and out of all the FX loop jacks several times and work the switches a bit.
FX loop schematic: TL10-62-02 (1998) iss6.pdf