Howdy,
I recently cleaned the pots on my 1975 Yamaha g100 412. I truly thought the bass pot was shorted out given the symptoms. I could not believe the results from a good cleaning..like brand new now. So my Fishman SA 220 was having the same issues when I adjusted the treble on channel #1...the clip light even came on. But after reading numerous post I really did not want to disassemble the amp(sounds like quite the process after reading other posts) to try cleaning the pot. So I thought I would try the following. I took a piece of 1/4 inch (inside diameter) clear tubing and cut off 1/2". I unscrewed the nut holding the pot to the "face-plate". I gently "screwed" the tubing over the treads on the pot till it tightened up (bottomed out). I used the "factory cut" on the tube because it was a perfect 90 degrees to insure a good seal when it "bottomed out". Then I inserted the red straw of the contact cleaner down along the side of the shaft, tightly held a piece of tissue around the top to reduce the amount of cleaner escaping and sprayed. In between spays I rotated the shaft. After 3 good spray I checked it out...did not solve my problem. I repeated the process two more times and wow..it finally worked. I did notice the pot feels..hmmm..."dry" compared to the other controls. I'm assuming the cleaner removed any lubricant there may have been on the shaft and this may be the reason it took so many attempt to finally get it to work.....but it worked and I did not have to dissemble the amp. The amp was used 20 hours in the past week and no return of the problem. Just one word of caution...wear safety glasses...and of course read the label. I'm building a better version of the clear tubing "tool" It is sealed at one end and the red straw is super glued through a small hole in the side. This should provide more pressure, forcing the cleaner into the pot past the shaft. Hopefully I will not need to try it out for a while.
Have a great day.
PS:I hope my instructions were easy to decipher.
I recently cleaned the pots on my 1975 Yamaha g100 412. I truly thought the bass pot was shorted out given the symptoms. I could not believe the results from a good cleaning..like brand new now. So my Fishman SA 220 was having the same issues when I adjusted the treble on channel #1...the clip light even came on. But after reading numerous post I really did not want to disassemble the amp(sounds like quite the process after reading other posts) to try cleaning the pot. So I thought I would try the following. I took a piece of 1/4 inch (inside diameter) clear tubing and cut off 1/2". I unscrewed the nut holding the pot to the "face-plate". I gently "screwed" the tubing over the treads on the pot till it tightened up (bottomed out). I used the "factory cut" on the tube because it was a perfect 90 degrees to insure a good seal when it "bottomed out". Then I inserted the red straw of the contact cleaner down along the side of the shaft, tightly held a piece of tissue around the top to reduce the amount of cleaner escaping and sprayed. In between spays I rotated the shaft. After 3 good spray I checked it out...did not solve my problem. I repeated the process two more times and wow..it finally worked. I did notice the pot feels..hmmm..."dry" compared to the other controls. I'm assuming the cleaner removed any lubricant there may have been on the shaft and this may be the reason it took so many attempt to finally get it to work.....but it worked and I did not have to dissemble the amp. The amp was used 20 hours in the past week and no return of the problem. Just one word of caution...wear safety glasses...and of course read the label. I'm building a better version of the clear tubing "tool" It is sealed at one end and the red straw is super glued through a small hole in the side. This should provide more pressure, forcing the cleaner into the pot past the shaft. Hopefully I will not need to try it out for a while.
Have a great day.
PS:I hope my instructions were easy to decipher.