Noisy Input Pot : Lexicon Reflex

[yekuku]

hi guys ,
i have a Lexicon Reflex effects proccessor.
when using the input pot for adjusting the gain, noise is produced.Even if nothing is connected to the input the same thing happens.
by searching the forum i understood that this problem may occur when:
1) there is dirt or dust on the pot.
2) the pot is damaged
3) DC getting to the pot via a leaky coupling capacitor
Is there sth else i must look for?
I cleaned the pot with a philips contacts cleaner but the problem persists.
I tested the pot with a multimeter and it seemed to work fine.
when adjusting the pot , i get noise in random places.
it is probably a leaky coupling capacitor but i dlike to have some experienced advise before going into that.
Does anybody know where can i find a Service Manual for the lexicon reflex?
Any help/suggestion about this would be very much appreciated.
thanx

[Extreme_Boky]

The pot can be noisy because of stubborn dirt build-up. The graphite (plastic?) resistive track can be damaged or the wiper could be misaligned…

Next, try to measure DC voltage. Use CRO (or good milivoltmeter). Normally – there should not be any DC voltage present at the pot input (but this can depend on the input topology…). There may be a buffer section placed BEFORE the pot that’s spitting out some DC current.

I would look at replacing the pot with something really cheap ($2 dirt cheap dual pot from Dick Smith…) – just to rule out the original pot fault. If it turns out that you are getting the same problem with brand new good working pot, try to obtain the circuit diagram and post the input CCT. I should be able to help you further…

It’s hard to guess what causes the problem. You mentioned that problem did not go away after you washed the pot… so it could be electronics’ problem.

Also, remove the pot (if it’s not too much of a hassle), dip it in to isopropyl alcohol and turn the wiper vigorously 10 times from end to end. Dry it, install it back and if it does the same thing, it’s probably electronics’ problem.

Boky

[yekuku]

posted by Extreme_Boky


I would look at replacing the pot with something really cheap ($2 dirt cheap dual pot from Dick Smith…) – just to rule out the original pot fault.

done that and the new pot is workin fine. But of course its not identical so it doesnt fit right.
i opened the faulty pot , cleaned it carefully with a contacts cleaner spray but the problem persists.
It seems that some of the graphite is wiped out.
So i am planning to order a new pot , i ve just contacted lexicon and they seem to have spare parts available.
Note: Lexicon gives access to all their discontinued products service manuals, just by contacting their technical support. So if anybody is interested , he can grab some...

Boky thanks for helping me out , bro