Problem Behringher PMP 1280s

[burntfuse]

I have a Behringher PMP 1280 with output problems. I have disassembled the amplifier and have found that a 30Mohm resistor on the output of the amplifier is burnt. I am unfamiliar with this type of output circuit as it differs from every other amp I have worked on in the past. The Circuit traces are intact and unburnt and the Neutrik connector board appears to be undamaged. This amplifier circuit seems to have only a single output transistor on each channel, and then two smaller transistors mounted next to each. The mixer and effects stage and all line level outputs appear to function correctly. I am not sure how to proceed as I do not understand the purpose of the 30Mohm resistor, unless it is some type of overload protection and possible acting as a shunt or fuse?

If the amplifier is fried to the point that the costs outway the time to fix it all may not be lost, If someone with a schematic can tell me what the voltages are for the 5 power(4 black, 1 red) wires to the mixer section are. I am thinking that it may be 48v dc as the mixer does have phantom power. If I can match the voltage and amperage then I may be able to use it as a stand alone mixer and/or wire it to another two channel amp as the mixer section is completely self contained.

any help greatly appreciated, thanks.

[Enzo]

The output is odd in that there are two smaller output transistors on one rail and one larger one on the other - so three outputs.

The resistor is 30 milliohms, not 30 Meg. Just in case.

The resistor is in series with the output and is used to sense current.

Check that 250 and the pair of 9640 MOSFETs for shorted.

Also, there are a couple triacs on the output connector board, make sure they are not shorted - one per channel - a short would be right across the output.

Are both channel outs dead from the power amp?

There are two sets of main power wires running from the power amps to the power supply board. There is also a smaller 6-pin cable from the power supply to the power amp. You can unplug the two heavy wire power cables AND the small 6-wire one from the power amps, then just continue to run the mixer portion with the existing power supply, if it is working.

If the power amps are blown, the power supply usually shuts down. But with the main power disconnected, the amp will sense that and send a shut down signal to the power supply. That is why you need to disconnect the small connector from teh amp as well as the two large ones.

Be aware that with no power amp connected, those main power supplies will hold a charge for a LONG time. You can come back a half hour after you unplugged the thing and still find 60v in each supply. WHAP!

I am an authorized repair station for those, and I cannot for the life of me figure out a reasonable way to get them apart. I always wind up pulling everything off the panel and it is a pain in the ass. If you have discovered some more convenient method, please share it.

[e_c_mccollum]

Be very cautious with the pwr supply caps for the pwr amp. I have a pmp5000 which generates -/+ 90vdc. If you know how to safely discharge them, it will help you alot. Good Luck

[burntfuse]

Thanks Enzo, That helps considerably. I think I will forego attempting to repair the amp section, as money is tight and it is just as useful to me as standalone mixer. I also think this amp was designed for ease of assembly at the plant, and completely uneasy disasembly at the bench. I had to completely remove the chasis from the housing, so I don't think there is any other way to gain access to it's seperate modules. Oh and if they would use just a little more hot glue on the connectors maybe they would be impossible to disconnect at all (last sentence sarcastically spoken) :^).

[Enzo]

Spray the hot glue with some freeze-it, and it then is easily shattered. Try it.

[burntfuse]

Thanks, I will do that. I don't have any freeze-it but I do have some canned air, sprayed upside down it should achieve the same result.

[chickenwatt]

Hi Enzo, I am servicing a PMP-1280 and after an hour disasembling the unit I have been unable to reach and take out the amplifier, do this console have a treaky way to take this amp apart?
Have pictures on how to take the amp out?

[chickenwatt]

Ok I did find the way to disassemble the power supply and amp board, whoever design this should be candidate for a NOBEL for idiot, what's the need to complicate things to us that we are going to solve a problem to it's owners, my god, I have one channel good and the other not sounding, all mosfets are ok, I interchaged IC1 and IC2 and the same problem and get to the conclution that the big IC there HCA9001 is the guilty, as every other device is good.
I found it only on EBAY from Hong Kong,
Do you have had this same problem in your experience?