Very Dumb problem seeks Very Dumb solution

[jasonallenh]

I've got a G-Pultec here (a very simple project) that was working as expected, but slightly bumping the bypass switch or first boost pot is causing the audio to partially cut out (either overall level or low frequencies). First guess here is that the pots or switch contacts are dirty, but before my can of deoxit arrives, does anyone want to chime in with any other possible issues (maybe circuit-specific to the G-Pultec)?

 

[mjrippe]

Check your solder joints

 

[jasonallenh]

Check your solder joints

This is a previously-working circuit that has since stopped. Solder joints aren't the issue here. I did see what looked like dried coffee in the case, so that's certainly a clue. Now how to get this crud out of the sealed rotary switches (gulp)

 

[industrialarts]

As far as cleaning goes, I will say that sealed pots are necessarily as sealed as you think. I would start with rubbing alcohol, which has become my go to 'solution' for cleaning just about everything. I seldom revert to anything else nowadays, even with the worst culprits. The naptha based solvents have caused me a lot of problems, especially with plastic elements. 70% alcohol is fine, I have a little bottle with a needle style applicator that gets into small spaces. Compressed air can also be very helpful. Exercise the pot and/ or switch a lot

I would also advise that if you do use something like De-Oxit, the less you use, the better.

If after that you still have noise or intermittents, then the component would need to be replaced

 

[hodad]

This is a previously-working circuit that has since stopped. Solder joints aren't the issue here.

This is not necessarily the case. It's worth your time to make sure there are no problems with the soldering.

 

[L´Andratté]

This is not necessarily the case. It's worth your time to make sure there are no problems with the soldering.

I have noticed this too, probably barely functional solder joints going dysfunctional over time (by oxidation or vibration or whatever).

 

[cyrano]

My dad's Yamaha CR700 receiver is full of visible/invisible cracked solder joints. The first time I repaired it, the cracks were obvious, because they were sparking. The last time, a few years ago, I touched up every solder joint. That revived it for a few years. The last time it failed, I gave up and bought him a new NAD. Then my mum moved the speakers to the attic...

As it's in the living room, moisture isn't a problem. Nor has any of the other gear had cracked joints. One X-rated cap failed on the DUAL turntable. Nothing else. Vibration also isn't an issue. Nor unleaded solder, as the thing is too old for that.

I'm guessing the weather conditions while it was being produced were unfavourable. Just like the Liberty class transport ships during WWII, that broke in two while in harbour. It was discovered later that moisture in the air caused metal fatigue.

 

[jasonallenh]

Update- I replaced one pot that would not clean up no matter what I did- that helped. However, I'm now able to recreate my friend's initial issue. Just bumping the lorin rotary switch the right way causes a short that causes either a signal drop or a 'bypassing' of that filter. I used a little bit of deoxit fader (plastic safe) to try and help, and I'll go ahead and reheat the solder joints (there aren't that many anyway). but I am concerned that the switches are too full of dried sh*t to ever really be cleaned up.

 

[cyrano]

In case the switch is very dirty, unsolder it completely and throw in the ultrasonic cleaner with some water/IPA mixture...