Hello. I have a bit of an issue with my powered mixer. My Behringer PMP4000 has an issue with output. The sound is very under-powered and distorted even at the lowest levels. The cooling fans do not energize and even the small distorted sound it does pass through, seems to fade to mostly noise only. Any and all help would be greatly appreciated. I did have an issue with the PSU and had to replace T3 and T4 power Mosfet's, which gave me power to the amplifier board again but I am not sure if the current issue is because of a low power supplied from the PSU or if it is a Amplifier board. The schematic for this unit is not readily available, but the Behringer PMP6000 schematic is available in many places and that unit is very similar to the 4000. The SMPSU29 Power supply board in both units are exactly the same. Again, any and all help would be greatly appreciated. Thanks.
Some clarification
Ok, Here is where things sit after replacing the Mosfets T3 and T4. Upon power-up, the unit comes to life. A small audible click is heard from the Amplifier board, The fans still fail to energize, Amplification of input from any source is weak and distorted. The amplification of the audio is moderately clear for a split second when volume is initially turned up, and degrades quickly, with a fading of the source audio moments after to a point of basically static and distortion. Seeming almost like the amplifier board is not receiving the power it needs to cleanly and clearly output an amplified signal. The diagnosis continues....
Ok, Here is where things sit after replacing the Mosfets T3 and T4. Upon power-up, the unit comes to life. A small audible click is heard from the Amplifier board, The fans still fail to energize, Amplification of input from any source is weak and distorted. The amplification of the audio is moderately clear for a split second when volume is initially turned up, and degrades quickly, with a fading of the source audio moments after to a point of basically static and distortion. Seeming almost like the amplifier board is not receiving the power it needs to cleanly and clearly output an amplified signal. The diagnosis continues....
I'd apply a sinewave to an input, and scope it out along the signal path.
At least before / after the channel fader, and then the main mix fader(s).
If all that checks out, then the issue's in the power amp section.
At least before / after the channel fader, and then the main mix fader(s).
If all that checks out, then the issue's in the power amp section.
Unfortunately I have no scope. Have just ordered one but even still, I have never used one before so the learning could be interesting. As far as the Mixer part of the system is concerned, using the PMP4000 with the amp board disconnected and using an external amp, the mixer works fine, so I know it is not in the Mixer part of the circuit. I have found that there is no voltage on the secondary side of TR4, Neither the A nor B secondaries show any signs of life. I know this may be out of the purview of this site, however I was hoping that one may have had some experience with this unit.
Hey DaedalusWren, wondering if you ever figured out what was wrong with your PMP4000. My son and I bought a PMP6000 for $25 that wasn't powering up. We replaced a blown diode on the PSU board and got the mixer to power up and it works great. Being a hobby level electronics person, I was really excited we got it to work. However, once we tried out the power amp side we found the signal to be exactly like you were experiencing, almost no volume that was extremely distorted. And the fans don't work as well.
All of our mosfets seem fine on the PSU but just like you I've noticed no power coming out of the secondary side of the TR4. Almost everyone has said it's highly unlikely for a transformer to fail but I can't seem to find any other issues with caps or resistors or diodes. Seems like the power amp board just isn't getting any power.
Curious to know what you came up with. Thanks!!
-brian
All of our mosfets seem fine on the PSU but just like you I've noticed no power coming out of the secondary side of the TR4. Almost everyone has said it's highly unlikely for a transformer to fail but I can't seem to find any other issues with caps or resistors or diodes. Seems like the power amp board just isn't getting any power.
Curious to know what you came up with. Thanks!!
-brian