Fender M-80 Chorus Troubleshooting

[ACEE]

Hi all,
I've noticed the strangest problems with my M-80 Chorus and was hoping someone could give me some direction. My clean channel is all messed up. When I jiggle the input jack the signal cuts in and out, the volume knob becomes unresponsive, the bass knob at 2 seems to go to 11, treb and mid knobs become unresponsive. NONE of this happens in the gain channel. I looked at the schematic that Enzo so graciously provided (thanks again for that) and I don't see how this is possible. The signal goes through the clean channel before it reaches the gain circuits. The switch either sends the distorted signal through or sends it to ground (on/off respectively). If it goes through the clean channel regardless, how does the jiggling not affect the gain channel? I did a semi-check of the solder joints of the input jack and they look alright. Any ideas would be greatly appreciated. I'll keep probing.

[Enzo]

Because when you wiggle the input jack, you are not only wiggling it, but also everything on the board it is soldered to.

Pull the boards and look closely at the solder under every control. Also while the board is out, look for cracked controls. When they are tighened into the panel they don't move. But the plastic wafer that is the heart of the pot can crack across, leaving the pot either open or intermittent. Cracked pots can either fall apart or get really "flexible."

And if nothing else, plug a signal into the front and don't touch it. Now use an insulated probe - translation: a stick... a chopstick works nice - and gently push on each part on the board, looking for any part that sems to respond to a nudge. they should ignore all nudging.

[ACEE]

That's really interesting. I was thinking of replacing the pots anyway because I was told that scratchy sound you hear (out of the speaker cab) when you adjust a knob is due to a dirty pot. Maybe there's something else wrong with them.

Quick edit: In my first post I said the signal goes through the clean channel before it gets to the gain channel. That's wrong. I double checked the schematic this morning and found the signal splits between the clean channel and the gain.

Thanks a lot for your suggestion Enzo, that will be the first thing I do. Unfortunately I can't do any continuity tests yet because I don't have a meter, but I plan on getting a Fluke 179 soon.

[52 Bill]

If the pots are dirty, use a spray cleaner/lubricant. No need to replace them unless as Enzo sez, they have broken off where the case meets the mounting lugs.