Behringer 880S Left Main Cuts out

[chaddz3]

Hi, I have a Behringer 880S powered mixer that I have has an issue where the Left Main starts cutting out after about an hour and a half of use, The right channel is ok. Opening it up revealed to Amp modules that are ID'd as DPA400 PCB302060REV E. I am wondering if the cutting out could be caused by a bad MOSFET transistor or if something else is the cause. R18 and R19 on the board are slightly darker in the center of the resistor like they have been warm. Also along the block of Aluminum just right of center on the board are 4 components that look like MOSFETS, but are labeled as D9, D2, D7, and D10 on the board.

If I am unable to just order a new board complete, what would be the most likely cause of the cutting out and what are the part numbers for sourcing from Mouser or Digi-key to repair my current board myself... The Numbers on the components are faded enough i can no longer read them.

I really appreciate any assistance anyone could give me on this.

Thanks

[Enzo]

My very first suspect would be the things that get the signal TO those power amps. I'd be looking for a bad contact in a power amp in jack or something like that. The slide switches that assign the power amps are always suspect, and the speaker processing switches as well.

If you still doubt the power amp modules, exchange their input connectors. If the same one still cuts out with its new inoput signal, then it is at fault, but if the problem now transfers to the other side,then the trouble is coming in from the mixer.

[chaddz3]

Ok heres what we have so far.. I ran the system under test for about 30 minutes (the problem didnt occur this time) but i did notice the left channel's amp heatsink was beginning to get warm fairly quickly where the right channel's heat sink stayed relatively cool, The speaker switches on the front have always stayed in L MAIN R mode and speaker processing has always been off (Never used this feature) When the channel would cut out, the level meter for that channel would still show activity, and the audio in connectors appear to be solid. I will continue to try to get the thing to mess up again so i can switch connectors and see if the problem follows, but assuming the mixer is not the problem (because of the heating issue on the one amp) are these modules easy to obtain and if i do need one where can I get one from? If replacing it isnt an option, what are the part numbers for T1, T2, D9, D2, D7, and D10 since that heat sink is heating up, i am assuming its one of those pieces.

[Enzo]

The transistors are marked, I think they are IRF640 or something. I sincerely doubt the diodes are overheating.

You may never use those slide switches, but the signal is still routed through them, and if those switch contacts get oxidized or otherwise dirty, you can lose your signal. I highly recommend flipping them back and forth a few times to clear the contacts, and a squirt of cleaner wouldn;t hurt.


I can't get those power amp modules and I am an authorized service center.

[chaddz3]

Thanks Enzo, I really appreciate the advice..