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I have a Fender Princeton Chorus amp that I am repairing for a customer. The amp has serious scratching noises when turning the pot, in fact the gain pot is very scratchy (like very loud when turned) that sometimes completely cuts off sound when I touch the gain knob in any way.

I took the amp apart and I can not find anywhere the solder is damaged or broken. Everything looks pristine and in fact the pots turns tightly without any play. The amp was not easy to disassemble as I can't even access the pots without taking the entire circuit board off.

Any advise here? I plan on reflowing the solder anyways in case there is a microscopic defect somewhere, or take the gain knob off, disassemble the pot, and maybe some spring inside is loose?? Or perhaps replace the pots.

It took me an hour to take it apart and will take me another hour to reassemble it to find out if the fix even works.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

There is no spring inside those pots. What you have is a surface mounted circuit board, made with cheap components. They are not designed to be repaired. Fender recommends replacement with a new circuit board. They can be repaired, but its not easy and the correct cheesy part is hard to find.

_________________
"Act your age, not your shoe size" - Prince

Pots get dirty and wiper contacts oxidize. Very common in both instruments and amps.
First step is to get a shot of electronics contact cleaner like Deoxit into the pot, preferably through openings in the back, or even down the shaft in front. Both methods work, although spraying from the front is more messy. The stuff creeps everywhere, but doesn’t affect finishes. Work it back an forth several times. 9 out of ten times that will cure the problem, at least for a while.
If that fails, you replace the pot.


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Kinda weird a lawyer making good money cheaps out on his gears... but I guess it's his money. At least he's willing to pay according to the amount of work it takes to fix it (but he would have actually saved money AND given me more work had he bought high quality gears that are easily serviced).

The circuit board isn't that hard to desolder and repair assuming I can find replacement pots. Unfortunately this pot is completely sealed, like really well sealed that I can find no opening to spray contact cleaner into. I guess I'll just remove the offending part and find out where I can find replacements. Radio Shack like shops are everywhere in Taiwan and they always have the parts.

Hopefully these experiences will teach him to not cheap out on things.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

I really don't get the insult directed at your client...

it's a known name brand which most people would assume implies a certain level of kwality (misspelling intentional), probably made in the CCP and actually *edited*.

either way, pots getting scratchy is a fairly common issue...I've had it happen with both amps and guitars I hadn't played in ages and those were American made products (though I can't honestly say where the pots were manufactured, but I can say my stuff is from the 80's)...my solution was to simply rotate the pots back and forth repeatedly and the problem was solved.

I suggest you be appreciative of the fact you have incoming work as opposed to complaining about stuff like this...next time instead of whining (you want some cheese?) take a confident approach about it all and assure the customer you know how to fix it since you now have experience in it...

oh, and remember a certain law of physics...it's called entropy...read up on the concept and come to grips with it...

The amp in question isn't made by CCP. Says made in the USA on the board and has a stamp saying "assembled in Mexico.

I wasn't looking for advise in dealing with people. I'm bad at it and sorry if I made some mistake.

I can't really find the pots in Taiwan, at least not ones that look like the ones on the amp and plus I do not know how the sound would be affected if I used non Fender parts. I have advised the client on the costs and I'm waiting for him to get back to me.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

I’m repeating myself, but
Shoot some contact cleaner down the outside of the shaft so it runs down into the pot. Stewmac even sells a gizmo that fits over the pot shaft and keeps the spray from going everywhere. It’s not essential, but is less messy. Work the pot back and forth. 9 times out of ten that will clean up scratch pots.
Like I said, I’m repeating myself.


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Sounds like some dirty pots. See if you can get some contact cleaner like De-oxit and soak them and work them back and forth. sometimes they'll clean up really well and sometimes they won't.

If you can get to the pots and they need to be replaced. Try https://www.mouser.com/ as they pretty much have every component imaginable.

The pots are sealed, people. No cleaning possible. It was designed to be disposable.

_________________
"Act your age, not your shoe size" - Prince

The pot looks like this

I found a site that sells them, genuine Fender part. Not sure if I want to just replace it with some Chinese part. I also can't find pots that look exactly like that. If there is any gap it's microscopic and I had to take the whole amp apart just go get at it since it's sealed everywhere else.

I think it's more than just a dirty pot. I mean the amp sound completely goes out at times just touching the wrong pots. But the inside of the amp looks pristine, new, etc. and yet the pot is scratchy and broken.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

I never tried it but I was curious too, but didn't... Since you have found the proper pot then maybe you are willing to try this experiment. Drill a hole in the pot and inject the cleaner in.

Actually an update... I just kept turning the pot and it seems to be clearing up the issues. Basically this amp doesn't really justify the amount of money spent on pots... this amp is like 250 new. I'm trying to get him to get tube amps as he seems to be suckered into buying new fangled modeling amps. I told him if it ever breaks there's no way to fix them. All surface mounted components that is hard to track down. Like trying to fix a bad cap on an iphone but since the cap is the size of a grain of sand.. forget it.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com