Behringer PMX2000 Fried!

[brant]

Hey there! I have a Behringer PMX 2000 power amp and the amp module is burnt up very badly. I have been communicating with Enzo via E-mail and we have decided to post this project here to share with everyone. I think what we are going to do is isolate the pre-amp/mixer section and re-engineer new amps.

Enzo- I powered up the unit today in order to test the pre-amp. I plugged the monitor out and L,R out seperately into my guitar amp and with a microphone tested the mixer. Channels 1 thru 4 seem to function OK 5&6 have no output.7,8,&9 have a weak signal and no monitor out. #10 has a good signal. The unit starts to smell hot after several seconds and I can't find the source. The Ic's and visible components on the mixer section all look OK and no sign of burning or smell of smoke. The amp section however has a large black patch and lots of smoke damage at the site of the lower amp between the two heat sincs. Also on the reverse side of the amp circuit the IC6 is burnt. Everything else on this side of the board looks OK. There are 5 other surface mount Ic's on this panel do they have any relevance to the pre-amp. Ie: could IC6 control the output for channel 5&6? The IC6 is so badly burnt that there are no visible #'s Can you provide a part # or sell me that IC? My thought is to replace IC6 and maybe get the mixer working properly before we proceed to next step. How can I make sure the power is cut to the amps to ensure that nothing else burns? I removed the fuses and the whole unit is dead. Thanks for now....BRANT

[Enzo]

The power amp provides the power supply for the preamp. There is also a power-up mute signal to the preamp. otherwise the power amp has nothing to do with the preamp, and certainly not individual channels.

You have the function listing of the ribbon cable to the preamp. All you see there is power supply, the mute, and L and R signals. No other circuits.

If the amp is still getting hot, look into the power amp. Remove any shorted power transistors from the board. I find it easier to snip their legs off near their body. Toss the old part. Now it is easy to remove the remaining leg bits from the solder holes. That alone should stop a lot of burning.

The high voltage wires from the transformer just plug onto fast connectors at the end of the board. You could just pull them, but I think we'd have to fudge the mute, since it refers to V-.

As I mentioned, IC6 is just a 4580 dual op amp in a SOIC package. I'd get them at Mouser.

There are five little ICs along the edge of the board on the bottom side. From the power supply end they are: IC6,5,8 and then 7,4. The full size ones - 6,5,4 - are all 4580. The two smaller ones are the limter chips, 3080 type.

[brant]

Ok I'm getting started on this re-power. If I use a different amp module I may have to use another transformer with a different voltage. What does the phantom power do? Can I eliminate it? Or do I still need +48 volts going to the front? .....BRANT

[Enzo]

Phantom power is +48VDC and serves only one purpose. It is there for microphones that require phantom power. The mixer will work just fine without it as long as you don't connect any phantom powered mics to it. They won;t work. WOn;t hurt the mixer, but those type mics will not function.