mixer Main out volume fades in and out?

[briancayko]

i have a Behringer SL2442FX-Pro, one of the main outs fades in and out while the other main out channel has a consistent output level.
I have the mixer taken apart and have pictures if that helps, an electrical engineer friend said it sounds like a bad resistor that overheats and causes the fade out and then cools down again and allows the fade in and so on. any input would be helpful as to what i would need to replace.
thanks,
Brian.

[Enzo]

Nah, nothing overheats in the signal path, there is no current anywhere.

Each MAIN out has an insert jack. That jack is probably dirty electrically. Pole a plug into and out of it a couple times and see if it either wakes the channel back up or if it causes the symptom when it is otherwise behaving. The cure is usually as simple as spraying contact cleaner down the jack, then poking a plug in and out to exercise the contacts inside.

If you look at those inserts, and can "read" the legs on the circuit board, you will find the angled corner leg is sleeve (ground) and the pairs of legs on either side are sets of contacts. measuer resistance of those contacts, they should read less than half an ohm. If they read something low but higher than that - 2 or 3 ohms for example - you WILL have a problem. 2 or 3 ohms won't interfere, but the fact the resistance is that high tells us the contacts are not healthy, and tomorrow they may not measuer so low. Clean them.

On those inserts, the tip is send, and the ring is return, so you can use the jack as a break point for troubleshooting before or after.

The other source of trouble can be the litttle assign push buttons.

Note that each input channel also has an insert jack. In my experience, in these mixers, the insert jacks and the little push switches are the main source of trouble. Those and the sliders. When I get one of these in for service I just automatically clean all the insert jacks with deoxit, then I pop all the little button caps on the assigns and mutes and such buttons, and squirt a drop of deoxit down beside the button shaft of each to clean them.

[km6xz]

Odds are that Enzo is right on the money, but your description does not fit the common use of the term "fades". Does it abruptly change and at times sound distorted when weak or does it fade as in slowly ramp down or up in level. "Breaking up", "cutting out" and "fade out" suggest different sorts of problems and solutions. To clearify, what does the signal do when the problem is noticed?

[briancayko]

okay, thanks for the quick responses, so did some more troubleshooting to be more specific as the type of audio loss I was experiencing. I found out that both the Main L and R XLR and 1/4" outs result in the same loss. I also found out that it was "cutting in&out / Breaking up" when I would physically move the boards around. for example the section of the mixer that has the main outs is connected to the sub out/main out section with the ribbon cable. well, when moving those sections around I would experience either break up or complete cut out, then I could get it to come back in if I tapped on the boards again physically jarring them I guess.
I hope that helps diagnose it a little bit better, I planned on going to pick up some contact cleaner this afternoon to clean the inputs and faders/eq etc. but thought I might wait to see if the new info gave you any other leads or suggestions before doing so.

thanks again for the quick responses.
brian.