JC-120 Chorus is making my wife seasick!

[onthegreenline]

Help! Just was given a slightly beat up but great sounding original (rocker switch) JC-120 from a friend for my upright bass and rhodes... It was in perfect working order with the exception of some noise on the volume/EQ pots and a little hum. I cleaned up the board and pots with some contact cleaner and I'm quite pleased with the now-silent pots and the reduction in idle noise... my only problem is that the chorus produces what I would describe as a ping pong tremolo effect when activated - I know what normal chorus on a JC sounds like and this isn't it! You can hear the chorus, but it's accompanied by a 2-times per second vibrato/tremolo sort of effect and it's so obnoxious my wife threatened to kill the amp as it was making the piano sound like a honky tonk and causing her to feel seasick!

I know you can't adjust the rate/depth of the vibrato, and I've tried switching the speakers to see if this is a phase thing. All the solder contacts look good, and I can't find any components that look "blown", etc. The amp sounds great cranked on both channels, the vibrato works perfectly... any ideas on where to start?

[Don Moose]

I cleaned up the board and pots with some contact cleaner

Ooh. Contact cleaner on pots - badness. That can eat the elements in certain plastic pots (like I would bet are in a JC120). You may want to replace the chorus-related pots to see if that's it.

Is there a footswitch to control the vibe or chorus? Those contacts may be bad/broken.

My Schematic seems to have gotten away. Anyone care to post?

Sorry - tired - fiddle with the footswitch jack a bit before you bust the thing open and get out the iron.

[onthegreenline]

Don - thanks so much, nailed it! I've always been taught it was ok to sparingly clean dirty pots with a little cleaner... guess I was led astray. I replaced the depth and speed pots and the chorus is back to normal! I had to use 500K pots in place of the 250K, even Roland tells me they usually substitute 500K or 1000K when working on these older models. While I was at it I replaced all the pots (using new 500K ones) with the exception of the distortion, and the amp is much quieter and sounds like a new piece of equipment... thanks!!!