quick question about the Behringer PMP5000

[cowabungamusic]

I got one of these in trade over the weekend and it seems to work fine, except the fan does not run when you turn the unit on.... can anyone here tell me if the fan should run all the time or not? I would think, being that this is a fairly high powered mixer/amp, that it should run all the time instead of cycle. I have a replacement fan for it, but I thought I would stop in here and ask before I swap the fan out.

[Enzo]

Is the fan inert? Or does it spin once or twice and stop at power up? For that matter, might it spin a couple turns at power down? If it moves at all, the fan itself is likely OK.

And you can always unplug the fan from the SMPS and apply 12v to it... or whatever voltage it likes.

And while everything sits there, put a voltmeter on the fan connector - is there voltage there or not?


Wait, are there TWO fans? They would be in parallel, and not likely two would fail together. I don;t remember.

On the SMPS, T7 drives the fan, with T15,16,17 controlling it.

Fan runs on the -21v rail.

[cowabungamusic]

Is the fan inert? Or does it spin once or twice and stop at power up? For that matter, might it spin a couple turns at power down? If it moves at all, the fan itself is likely OK.

And you can always unplug the fan from the SMPS and apply 12v to it... or whatever voltage it likes.

And while everything sits there, put a voltmeter on the fan connector - is there voltage there or not?

I don't see it move at all, on startup or power down. It isn't locked up, I have the thing apart so that my service guy can check it out when he comes in, and I can spin it easily with my fingers. It's a 24 volt fan, I don't have anything that puts out 24v but Bill (my service guy) probably does. I will fire it up and check if there's voltage on the connector.


Wait, are there TWO fans? They would be in parallel, and not likely two would fail together. I don;t remember.

This unit only has one fan. So am I correct in assuming it should likely run all the time?

On the SMPS, T7 drives the fan, with T15,16,17 controlling it.

Fan runs on the -21v rail.

Thanks for your help, Enzo, I appreciate it. I will check first the voltage at the connector, then swap the fans and see what happens, hopefully that's all it will need. This thing has a butt load of power for being a powered mixer, I was pretty surprised, and it sounds pretty darn good too, but obviously I don't want to run it very long without the fan if it's supposed to run all the time. I figured I would ask here, so I have a leg up on getting it going, since this is my shop's and not a customer's unit. This way I don't take time away from customers' stuff getting repaired any more than I have to. I'm definitely not an electronics tech, although I solder pretty well and do a lot of guitar electronics mods and repairs, but mostly I'm a woodwind and brasswind tech. Thanks again, I appreciate it.

[Enzo]

Even 12v ought to spin the 24v fan, or a couple 9v batteries clipped together for 18v.

My expectation is it runs all teh time, speeding up when necessary, but I don;t recall really.

You definitely DO NOT want to operate the unit without the fans going.

[cowabungamusic]

Ok, so I put the known good fan in it and it runs for a couple seconds then shuts off. It does at least let me know the old fan wasn't working, as I can't get it to do anything when I put voltage to it. I guess I need to find someone familiar with the unit or someone who has one who can tell me if theirs runs all the time or not. At least I am a step closer than I was before, regardless.

[Enzo]

Then it is probably OK.

There is a thermal sensor on the amp. I'd be surprised if the fan was bad and also the drive circuit at the same time.

There is a small 6-pin cable from the SMPS to the HCA2400 power amp. Between pins 4 and 5 is a 330 ohm thermal resistor on the amp.

If you look on the amp board, connector X12, pins 4 and 5 should trace to the resistor. I don;t recall, but I'd bet it was on the heat sink, y'know? Maybe one of those little things with a screw hole tab. It will be labeled R2. Hit it with some heat and see if the fan wakes up.

Ah, I have a dead one here, right in the corners at either end of the heat sink is a small gray thing with a screw tab. R2 should be easy to read silkscreened on the board. Says 330 ohm, mine reads 100 ohms cold. ANyway, pop the lid off the amp board, and heat that part.