Behringer PMX2000

[e_c_mccollum]

I am looking for a schematic for a Behringer PMX2000 mixer amp.

[Enzo]

Good luck. Seriously. The company won't send them out, and as dealers we had to sign a non-disclosure agreement. We are specifically told not to share the drawings. I asked them what is a competent repair shop suppossed to do after the warranty? Their response was refer the customer to the nearest service center.

I cannot give you schematics, but I can answer questions. The 2000 is the box mixer, right? What is its beef? My experience with their power amps is that the MOSFETs fail and take out the 0.1 ohm - or whatever - ballast resistors. Doesn't usually burn up a ton of stuff like a bipolar stage.

[e_c_mccollum]

My customer thought is was a good idea to cover his mixer amp with a sheet to protect it from the dirt flying around. The fan inside couldn't get enough fresh air so one of the channels overheated. I am having to rebuild the complete channel. The other channel tests and works okay. I hope it stays that way but exposed to that much heat, only time will tell.

It turns out the thermal cuttoff swicthes on the heat sinks failed to open. I tested them on their heatsinks without the transistors mounted using a hairdryer. The meter kept showing continutity.

In my experience when a channel blows up, the thermal fan circuit messes up also. The amp is used in Mexico and it is very hot there. I will either wire the fan full power or disconnect it and use a 3" 120v fan wired to the power switch.

To figure this out, I guess I have no choice but to remove all the components on the bad channel (need to anyway), clean it up, and carefully draw a schematic of the fan circuit.

I love Behringer equipment.

[Enzo]

I am sorry, that model is not one with the MOSFET modules is it. Looks like conventional bipolars. If you need R# values or anything, please ask.

The fan circuit may not be working right, but it doesn't connect to the power amp. I don't know why the power amp failure would affect it either way. The fan circuit runs betwen the + and - raw voltages before the +/-15v Vregs (VCC2). I would guess those are about maybe 20 volts each? The fan itself runs off the neg VCC2 and a transistor to ground, T23, with a 4.7 ohm in series. T22 controls 23, and its base is controlled by a pair of 330k thermal resistors R28,29. If I had to guess, I'd bet those resistor/thermistors are onthe heatsinks. T23 is a type BD239. An EC short on T23 would leave the fan on full all the time

[e_c_mccollum]

I see what you are talking about when you say short E to C on T23.

The fan motor feels a little stiff but it will run. It looks like a cheap fan. At first, the motor looked okay (spun freely) until I ran it a while to check funtionality. The parts have areadly been ordered and there is no time to order a new fan from Mouser Electronics. He needs it this Saturday. I have called around to find out only 12v fans were availiable. I would have to drive 60 miles to Mcallen, Texas to get the fan. At the current gas prices, it will be a expensive fan.

I have found a 120v 3" Orion fan with ball bearings. I need to check the clearence in the case (fan deeper than the old one) before getting too far. I don't like plastic fans especially down here where it is very hot and humid. These dc fan may be standard issue but I noticed they don't last long here.

How can I set the dc fan circuit to "idle" since it won't be used anymore (for now). I don't want it to cause problems with the other circuity. Nothing test bad in the fan circuit but I am not sure about the thermistors.

I will retest the thermal cutoffs but still, they should have turned off the amp before the channel burned up.

[Enzo]

The fan control ckt has its own thermal sensors, they are not the same ones that would remove power.

All the fan control is is a couple thermistors controlling a couple xstrs, which control the fan. Disconnect the fan and the rest of the circuit will just sit there. It would be like pulling the bulbs from your dining room light fixture and wondering if the dimmer circuit on the wall will be OK. It will.

The fans may be plastic, but the motor shaft and bushings are not. Any motor can bet gummy. SOmetimes I peel the little label back and apply a drop of lubricant. Deoxit even works.

Let us know how the channel rebuild progresses.

[e_c_mccollum]

Thanks for a prompt response.

This amp should work awesome when finished. I will let you know.

The only other concern I have is the AC voltage input. Mexico has a poor electrical systems. The voltage/current can vary. Most Mexican bands have to use a generator because of this.

[Enzo]

Never hurts to use a line conditioner, there are constant voltage units that wil work quite well. Although these circuits are not regulated, so if the mains drop to 100v, then the amp will just produce less power.