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post #1 of 7 (permalink) Old 07-29-2002, 02:51 AM Thread Starter
 
Join Date: Feb 2002
Location: Helsinki, Finland
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Dirty pots in amp?

My trusty Marshall Valvestate 8040 makes horrible crackling and popping sounds when turning the volume pot and adjusting volume is very inaccurate. The reverb also turns on and off pretty randomly. I guess these have to do with dirty pots or something like that.

How shold I fix this? I've heard about spraying CRC on the contact surfaces of the pots, are they reachable by just opening the amp? I'm pretty bad in electrics, is there any condensators or such inside that could result in electric shock even when power unplugged?
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post #2 of 7 (permalink) Old 07-29-2002, 03:32 AM
 
Join Date: Jun 2002
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I had this problem too with my marshall head (too long time without playing it).this is a simple trick to try:turn quickly each pot right and left for 1 or 2 minutes....it's cure the pot very often, if not....wait another answer (cause i don't know further )
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post #3 of 7 (permalink) Old 07-29-2002, 03:51 AM
 
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the trick as told by black napkins will only push the dirt/dust away or to another area and its not a fix.

the way to fix pots that crackle it to clean them.

This can be easily done with pot cleaner. make sure you get a kind that wont eat thru plastic.
i use Deoxit only, but thats me.

to do this,
expose the pot- this may require serious tear down/rebuild of the housing depening on what you have but a valvestate just has the top 6 screws; (make sure you dont let the amp crach down when removing the last few screws)

then, on each pot, there is a small opening if you will, spay the cleaner in the pot and THEN work the pot left to right in full rotations for a minute or so. once you've done this once, repeat.
If this doesnt fix the problem,(almost always does if done correctly) then the pot will need to be replaced..
also be sure to check for cold solder joints before replacing the pot as well.


scott
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post #4 of 7 (permalink) Old 07-29-2002, 07:37 AM Thread Starter
 
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What about electric charges inside? Are there any big condensators to look out for?
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post #5 of 7 (permalink) Old 07-29-2002, 02:25 PM
 
Join Date: Nov 2001
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hmm... will this same fix work for pickup selectors and tone knobs on a guitar?

-Drew
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post #6 of 7 (permalink) Old 07-29-2002, 02:37 PM Thread Starter
 
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Well I just finished cleaning the pots with CRC contact cleaner and now they're smooth. There were some scary looking 2200uF condensators so I stayed well clear of them I think, same treatment works with guitar.
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post #7 of 7 (permalink) Old 07-29-2002, 03:40 PM
 
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Quote:
Originally Posted by Drew
hmm... will this same fix work for pickup selectors and tone knobs on a guitar?

-Drew
yes indeed it does!
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