Behringer PMP3000 failure analysis
I know this is an old thread, but since i found it, others may be looking here, too.
I am analysing a broken Behringer PMP3000. Be warned that the PMP power supply and amplifier section contain several terrible design mistakes.
Example:
When we look at the amplifier schematics available at electrotanya, you can see that the power stage output switches IRF250 and 2x IRF9640 are AC coupled. This has been mentioned before. What happens during power up? Capacitors C19 to C22 need to charge through the respective 18V zeners and 15K resistors. Now, depending on power-up speed, all output switches will get partially conductive at the same time, to effectively shorten the PSU. That means, during the softstart phase of the power supply (current limited by the two 22 Ohm resistors mentioned before), the amplifier switches get hit hard. The designer tried to avoid the problem using circuits in front of the IXDD404 driver inputs, but thats just a confusion.
Lets not even think about 100 Hz supply line ripple. At least the zeners should have been 12V for clamping.
The power supply unit has similar horrible errors. As soon as you sharpen the overcurrent protection in order to really protect the IGBTs and the secondary rectifiers, the protection will trip each time at the beginning of the softstart phase. If you are able to apply some mods and cure that problem, you will find the protection now trips once more at the end of the softstart phase, when relay K1 closes. That means, without mods the IGBTs and the rectifiers are at risk each time you turn on the PMP3000. Ah, with a short in one of the amplifiers, the two 22 Ohm resistors are doomed to melt down. Ah, another one: Please observe that the existing overcurrent protection senses the current of one of the two IGBTs. And the other one doesn't need protection?
Sorry this had to be a little technical. In my opinion the Behringer Power Mixer line PMPxxxx cannot be trusted. Difficult to understand how those products made it onto the market. I think Behringer have been hiding their schematics because they are a shame. Now, if you buy a replacement power supply, or you get rid of your Behringer and buy something else, maybe of other brand, that won't last any better, since they copy from each other instead of doing their work.
I know this is an old thread, but since i found it, others may be looking here, too.
I am analysing a broken Behringer PMP3000. Be warned that the PMP power supply and amplifier section contain several terrible design mistakes.
Example:
When we look at the amplifier schematics available at electrotanya, you can see that the power stage output switches IRF250 and 2x IRF9640 are AC coupled. This has been mentioned before. What happens during power up? Capacitors C19 to C22 need to charge through the respective 18V zeners and 15K resistors. Now, depending on power-up speed, all output switches will get partially conductive at the same time, to effectively shorten the PSU. That means, during the softstart phase of the power supply (current limited by the two 22 Ohm resistors mentioned before), the amplifier switches get hit hard. The designer tried to avoid the problem using circuits in front of the IXDD404 driver inputs, but thats just a confusion.
Lets not even think about 100 Hz supply line ripple. At least the zeners should have been 12V for clamping.
The power supply unit has similar horrible errors. As soon as you sharpen the overcurrent protection in order to really protect the IGBTs and the secondary rectifiers, the protection will trip each time at the beginning of the softstart phase. If you are able to apply some mods and cure that problem, you will find the protection now trips once more at the end of the softstart phase, when relay K1 closes. That means, without mods the IGBTs and the rectifiers are at risk each time you turn on the PMP3000. Ah, with a short in one of the amplifiers, the two 22 Ohm resistors are doomed to melt down. Ah, another one: Please observe that the existing overcurrent protection senses the current of one of the two IGBTs. And the other one doesn't need protection?
Sorry this had to be a little technical. In my opinion the Behringer Power Mixer line PMPxxxx cannot be trusted. Difficult to understand how those products made it onto the market. I think Behringer have been hiding their schematics because they are a shame. Now, if you buy a replacement power supply, or you get rid of your Behringer and buy something else, maybe of other brand, that won't last any better, since they copy from each other instead of doing their work.
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