Marshall sealed pots

[Randall]

I have a JCM200 Dual Super Lead in with scratchy pots. It has the square green sealed ones. Sometimes I have had success by basically soaking the outside of the pot and having some of it seep inside enough to do the job. In this case, however it doesn't seem to be working. Anyone have an answer for this?

[mozz]

Not familiar with those pots but would blast right here.

[Randall]

Yes, I have tried that. After looking thru my notes, I see that I had noted on his receipt from 3 years ago that both volume pots were noisy, and that there may be a leaky cap somewhere causing it. I must have tried to clean it then also. Now that I think about it more, the volumes are acting like there is dc on them, but I did get the treble pot to calm down by soaking it and turning it a lot, so no dc problem there. I will go check for dc on the volume pots.

[Randall]

I think I have a bad cap. V2, V4, V7 and V9 all have some noise, and are all in common on the upper right of the JCM2-61-00 board. C21 has 228v on the feed side and anywhere from 24 - 119 v on the other side depending how V7 is dialed in. I'm going to replace it.

https://drtube.com/schematics/marsha...01)%20iss5.pdf

edit: Changed C21, it didn't help

[olddawg]

Are you measuring any dc on the pots or at the cap?

[Randall]

Yes, gobs of it. It was a bit tricky, but after I realized the dc went away when SW4 was in the other postion, every where exept C20, which acted like it was shorted, and it turns out it was. All is well now. I'm surprised it even worked with so much dc everywhere.