Fixing a crunchy pot

[N8Nagel]

Just thought I'd finished cleaning up a thrift store preamp - Luxman TP-117 if it matters - and after a couple days I have a new problem. The controls were ever so slightly staticky so I did a D5/F5 treatment. This seemed to fix a channel blending issue. Then I did a water/isopropanol/CRC QD treatment on the top sides of the circuit boards to get rid of the mess of tar, dust, and who knows what else. Then I gave it another F5 treatment just in case anything else has got in the pots while cleaning. Things were fine for a few days but now the balance pot feels super crunchy going through the left half of its rotation. No crackling, but it feels awful. I doused it in F5 but it feels like as soon as the carrier evaporates it will feel the same. Does anyone have any ideas? Maybe try to get some silicone grease inside on the wipers and tracks?

 

[redk9258]

Maybe needs lube where the shaft goes through the bushing.

 

[N8Nagel]

Doesn't feel like it as it crunches in the same spot every time.

I'm torn between trying to put some dielectric grease in through the openings in the pot to try to get a little on the wipers, and spraying in some non-conductive silicone lube. anyone care to comment? If this works, I have a Marantz 4270 that could use the same treatment as well, it's just not as bad.

I think the tech that worked on the 4270 (I can't fix tuners) used a contact cleaner by MG Chemicals that contained silicone, so I'm thinking maybe something like CRC 02094 (or the actual MG product that my tech used) might be the ticket - if I knew where to get it. Apparently my local electronics supply closed not long at all after the last time I stopped by there. D'oh.

 

[KingBubba]

You need some Caig Fader. Always use it after Deoxit has dried. Deoxit removes the built in lubrication and Fader will restore that. It is also suggested to follow Fader with an application of Gold or Shield, which protects the part from having the corrosion come back.

 

[UncleBingo]

Also, I would suggest looking for galling where the pot-shaft enters the threaded section of the pot. Aluminum pot shafts will often exhibit this behavior. Look for a black mess at the shaft/bushing junction (with the knob removed). Clean it with a dry rag while gently pulling the shaft in order to get any stray metal out of the junction. Light lubrication after doing this will discourage re-occurence.

 

[northpaw]

+1 on the shaft issues, as it sounds primarily mechanical rather than electrical. It may be that the water you used did not get completely removed from that recessed location, or get displaced by the solvents as much as you probably hoped it would.

 

[N8Nagel]

Well, I've flooded them again with F5 and I do mean flooded... we'll see how they feel when the carrier dries (it's been about a day)

 

[N8Nagel]

Update: it's friday and balance pot doesn't feel quite as silky as bass or treble but is OK... guess I just need to flood it again and call it good.

 

[N8Nagel]

Update: it's now the following Thursday and after another flooding with F5 it feels pretty good.

Am considering purchase of some F100 next time I place an order for stuff. Opinions? I have a lot of gear that has required abusive Deoxit/Fader applications to get the controls working well, and some of them (Marantz 4270) don't feel as silky as they could.