Behringer PMP4000 half working

[DaedalusWren]

The measurement unit for R52 & R39 were ohms. Guess I will end up pulling these to test them. You mentioned in a couple posts back that you would look at IC3 next as it is connected to IC4 which was damaged. Perhaps I missed something, but I don't recall IC4 being deemed damaged. If you think it may be damaged, I might as well replace it along with IC2 & IC3. They are cheap enough. I did swap out T3 & T4 though. Perhaps that was what you were thinking of?

[nickb]

On IC4 - sorry I was getting muddled with another thread where the PWM chip was bad. Ignore the remark.

[DaedalusWren]

Ok, I may have found something. R39, R52 and C32 were removed and tested. The Resistors measured out properly but the capacitor measured .327 on the 2K ohm setting. I pulled C34 also to compare measurements as both C32 and C34 are supposed to be the same value, and C34 measured infinite. Now, to try and clarify if C32 was faulty or C34, I tested a few more and all I tested showed infinite resistance, so I can assume that C32 is in fact faulty.

[nickb]

Ok, I may have found something. R39, R52 and C32 were removed and tested. The Resistors measured out properly but the capacitor measured .327 on the 2K ohm setting. I pulled C34 also to compare measurements as both C32 and C34 are supposed to be the same value, and C34 measured infinite. Now, to try and clarify if C32 was faulty or C34, I tested a few more and all I tested showed infinite resistance, so I can assume that C32 is in fact faulty.

Capacitors don't pass DC and therefore should measure infinite, ergo C32 is bad.

[DaedalusWren]

Ok, now seeing as though C32 is bad, could its failure cause a low voltage state at IC2 pin 1? I am not sure how that parallel coupling of R52 and C32 effect the circuit when in proper operation, and what difference there is when C32 is bad like this as it seems to me to basically be a filter. The short through C23 however would allow current through, lowering the total resistance of the RC circuit. (seem to be answering my own questions now.) Would it be enough to cause the low pin? Just trying to absorb as much as I can. Thanks.

[nickb]

Ok, now seeing as though C32 is bad, could its failure cause a low voltage state at IC2 pin 1? I am not sure how that parallel coupling of R52 and C32 effect the circuit when in proper operation, and what difference there is when C32 is bad like this as it seems to me to basically be a filter. The short through C23 however would allow current through, lowering the total resistance of the RC circuit. (seem to be answering my own questions now.) Would it be enough to cause the low pin? Just trying to absorb as much as I can. Thanks.

I think you did answer your own questions

If C32 is low resistance then the voltage across it will be reduced since V=IR. C32 and R37 do form a filter that prevents high going spikes from triggering IC3A. WHen going high C32 is charged through R39 ( IC2 has a very high impedance when high). That signal is low to shutdown and C32 doesn't do much filtering now as the output impedance of IC2 is very low in this case so discharging C32 quickly.

[DaedalusWren]

Ok then, that being said, and seeing as though this RC configuration is only a filter, I went and removed C32 and powered up the unit without the Amp connected. The fans came to life on high, as there is no control from the amp board. First signs of life! I then attached the amp and mixer board and it all worked like a charm. I have to find a ceramic cap to replace C32 and all should be beautiful again. The funny thing is, I just ordered a new board from Behringer three days ago. Should be here in a few more days. I was going to use it as a test board to compare probe measurements. It seems I now have a backup board. In the mean time. Would running the board without C32 pose any issues till I replace that cap?

[nickb]

Ok then, that being said, and seeing as though this RC configuration is only a filter, I went and removed C32 and powered up the unit without the Amp connected. The fans came to life on high, as there is no control from the amp board. First signs of life! I then attached the amp and mixer board and it all worked like a charm. I have to find a ceramic cap to replace C32 and all should be beautiful again. The funny thing is, I just ordered a new board from Behringer three days ago. Should be here in a few more days. I was going to use it as a test board to compare probe measurements. It seems I now have a backup board. In the mean time. Would running the board without C32 pose any issues till I replace that cap?

Good to know it's working again.

That's so sad that you ordered another board. You were doing so well and all that work... I'm sure you can get a refund. I really can't say for sure whether you'll have any problem w/o the cap as we'll never know what the designer had in mind. It would tend to cause it to come out of shutdown too soon but the soft start cap has to recharge it would probably be OK but why risk it?

PS: It's been really nice helping you. Many folk just can't follow directions or fail to present the results of the measurements coherently or even be polite. You excelled on all fronts. Oh and thanks for all the 'likes'. That was every generous of you.

[DaedalusWren]

It was easy to follow through with the repair when I had such a knowledgeable, helpful and diligent mentor. It was an absolute pleasure working with you in seeking out and eradicating this fault. I was not very optimistic on finding the problem when I first posted here, as many other sites came up with no help at all, but you sir, have renewed my faith in internet help and the kindness of complete strangers. I truly appreciate all the time you put into this with me and humbly thank you for all assistance.

Cheers and peace brother. (and for all that help, you deserved all the likes.)

P.S. If you hear of anyone with a Behringer PMP4000, PMP6000 or PMP1680s that is in need of a SMPSU29 Power supply. Let me know.

[The Dude]

I love how this turned out and the respectful way in which the results were achieved. We recently had a thread here that was quite the opposite. This is a great example of how it's supposed to work. Kudos!

[DaedalusWren]

Just an update. Had a busy weekend, hosted Karaoke on Friday night and DJ'd a dance on Saturday night with the repaired mixer and it drove my Behringer B1520 pro speakers without issue. Thanks again guys, especially nickb for all the help. I think next week I may pull out my Behringer nu3000dsp iNuke amp. It has an issue with one channel. Any takers on helping with that? Cheers guys

[Jazz P Bass]

I think next week I may pull out my Behringer nu3000dsp iNuke amp. It has an issue with one channel. Any takers on helping with that? Cheers guys

NU3000.zip

[DaedalusWren]

Thanks for the file Jazz.

[nickb]

Just an update. Had a busy weekend, hosted Karaoke on Friday night and DJ'd a dance on Saturday night with the repaired mixer and it drove my Behringer B1520 pro speakers without issue. Thanks again guys, especially nickb for all the help. I think next week I may pull out my Behringer nu3000dsp iNuke amp. It has an issue with one channel. Any takers on helping with that? Cheers guys

I have the schemo for the 3000 but not the 3000DSP.

[DaedalusWren]

I too have the schematic for the 3000 and not the DSP. I am hoping that the power amplifier and associated components will be the same.