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Thread: Behringer PMP4000 half working

  1. #36
    I'm a member? nickb's Avatar
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    Quote Originally Posted by Enzo View Post
    My concern was that he reported finding no signal on the transformer windings, and I doubt a meter could detect such even in a working unit.

    he also asked if he should measure the gates to ground. Regardless what they are referenced to really, none is to ground.

    I didn't want to see him basing measurements on a faulty premise.


    The shutdown pin on the IC4 has a bar over it, to me that means active low, so I would expect above the threshold to be NOT shutdown. Does the data sheet say otherwise?
    Gotcha When he said 'ground' I interpreted it as 'local ground i.e the source of each FET.

    I made the same assumption as you about active low. It's just not true as far as I can see. When that signal is high the PWM inv input is held low, the soft start cap is discharged, the PWM flip flop is held SET and both drivers are set to pull down via the OR gates. I also found a reference elsewhere that said the same thing. ALso, the lab test fixture shows a switch pulling the signal high to turn off. It just seems to be a documentation quirk and something of a timewaster for us.

    sg3525.jpg

    sg3525_test.jpg

    Go figure...
    Last edited by nickb; 01-07-2017 at 11:14 PM.
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  2. #37
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    Looking at the Lab Test pic, I would also assume the same. When Vref is applied to pin 10, bringing the pin high, the shutdown is in effect.
    IC3 has 0.64vdc at pin 6 and 5.04Vdc at pin 4 or Vref.
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  3. #38
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    Quote Originally Posted by DaedalusWren View Post
    Looking at the Lab Test pic, I would also assume the same. When Vref is applied to pin 10, bringing the pin high, the shutdown is in effect.
    IC3 has 0.64vdc at pin 6 and 5.04Vdc at pin 4 or Vref.
    Sorry been busy..

    There are 3 ways for IC3 pin 6 to be low:
    (1) Overcurrent via IC2c - since you don't see an output I don't think that is it.
    (2) Amplifier error via IC7. the amp is disconnected so that can't be it and
    (3) Undervoltage via IC2a. Check pin 7 it should be about 8.5V
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  4. #39
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    As far as you being busy, you have helped me a tremendous amount with this and i appreciate the time you have spared to aid me in this issue. So I do not mind you being busy at all.
    As far as this project goes, I think I will put all probed readings thus far here to avoid having to re-trace the progress in previous posts.
    Also, since you mentioned the amp being disconnected in the last post I thought I would ring through all the voltages again with the amp connected just to see if there was any difference. I found that the only difference was that Vcc increased by only o.o2Vdc with the amp connected while the rest stayed the same.
    The following are all probes taken thus far.

    IC4 pin 10 (shutdown) =3.7Vdc
    IC4 pin 15 (Vcc) =15.3Vdc
    IC3 pin 4 (Vref) =5.04Vdc
    IC3 pin 6 =0.45Vdc
    IC3 pin 12 =0.01Vdc
    IC2a pin 7 =7.56Vdc
    IC2a,d,c pins 6.9.11 =5.04Vdc
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  5. #40
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    as a side note. In regards to the function of pin 10 of IC4. The following was found regarding the SG3525, which from what I can gather is similar to the KA3525A (IC4) except for some different values. However the Shutdown is also labeled the same on this chip with the line over the shutdown name.

    Understanding SG3525 IC Pin Outs - Electronic Circuit Projects

    Pin#10 (Shutdown): As the name suggest this pinout may be used for shutting down the outputs of the IC in an event of a circuit malfunction or some drastic conditions. A logic high at this pin out will instantly narrow down te PWM pulses to the maximum possible level making the output device's current go down to minimal levels. However if the logic high persists for longer period of time, the IC prompts the slow start capacitor to discharge, initiating a slow turn ON and release. This pin out should not be kept unconnected for avoiding stray signal pick ups.
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  6. #41
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    Quote Originally Posted by DaedalusWren View Post
    As far as you being busy, you have helped me a tremendous amount with this and i appreciate the time you have spared to aid me in this issue. So I do not mind you being busy at all.
    As far as this project goes, I think I will put all probed readings thus far here to avoid having to re-trace the progress in previous posts.
    Also, since you mentioned the amp being disconnected in the last post I thought I would ring through all the voltages again with the amp connected just to see if there was any difference. I found that the only difference was that Vcc increased by only o.o2Vdc with the amp connected while the rest stayed the same.
    The following are all probes taken thus far.

    IC4 pin 10 (shutdown) =3.7Vdc
    IC4 pin 15 (Vcc) =15.3Vdc
    IC3 pin 4 (Vref) =5.04Vdc
    IC3 pin 6 =0.45Vdc
    IC3 pin 12 =0.01Vdc
    IC2a pin 7 =7.56Vdc
    IC2a,d,c pins 6.9.11 =5.04Vdc
    Nice table

    Well since IC2 pin 7 is > IC2 pin 6 then undervoltage is not the reason that IC2 pin 1 is low. So, we keep looking. Ignoring the possibility that IC3 is bad until other possibilities are checked, measure IC2 pin 10: I'd expect that to be zero. On the other hand it may be retrying. If that is the case then IC2 pin 10 will be greater than zero and we will have learned something interesting, namely that we have a overcurrent problem. This is an example point where a scope would give a quick unambiguously answer.

    The other possibility is there is enough current flowing through the DC shutdown optoisolator LED IC7 to turn the phototransistor on and so pull down the signal of interest. To check that measure the voltage across pin terminals +15V and DC_SD.

    Lastly IC7 could be bad, I suppose. And the other things I might have missed, of course...

    On the SHUTDOWN polarity, the data sheet for the pin compatible UC3525 from Texas Insts shows the shutdown as active high and gives some descriptive text the says the same thing. Bizarrely, in the their lab fixture, they have the shutdown switch pulling the signal low
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  7. #42
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    Ok. since we have both found indicators of the shutdown being active when Pin 10 of IC4 is logic high, The most solid I could find supporting this in the last sentence of the pin description. " This pin out should not be kept unconnected for avoiding stray signal pick ups." Meaning to me that the IC will function properly with this pin unconnected (logic low), but should not be applied as such. Assumption follows, that something is pulling this high and shutting down the circuit. Also seeing as these voltages are consistent, whether the amp it connected or not, can I tentatively assume that the amp board is not the cause of this state?

    The probes you mentioned in your last post were as follows.

    IC2 pin 10 = 0.00Vdc
    voltage across +15 and DS SD of the IC7 Optocoupler = 0.07Vdc
    voltage across the Emitter and collector of IC7 = 0.44Vdc
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  8. #43
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    With a reading of zero on IC2 pin 10 we can be fairly confident that it's not retrying. The main outputs will also be zero if so. We also now know the DC_SD signal is not the cause. That leaves R39, IC2, IC3, IC7, T7, R52 and C32. With the power off you should be able to measure the resistance across R52 - this will test R52 & C32. Do the same with R39. Try meter both ways round and pick the higher for these measurements. IC3 would be my next target since it's connected to IC4 which was damaged.

    With the others you can remove the chips one at a time or, if you are very careful, you can lift the pin connected to that signal of interest. Since this will be defeating the built-in protections and there still might be another underlying fault, it might be a good idea to disable the main switching path - I think the easiest way is to remove C21 temporarily.
    Last edited by nickb; 01-10-2017 at 07:59 PM.
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  9. #44
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    Well I have been dealing with a cold for the past few days so I have not done too much. I did manage to get out and check the resistors though. The readings were not what I expecting. Neither rung through as 47kohms, but as they are in circuit I imagine they would not.
    R52/C32 = .424 tested both directions with the same value.
    R39 =1.830 tested both directions with same value.

    I will get further into testing hopefully tomorrow.
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  10. #45
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    0.4242 and 1.83? What are the units? It may not be possible to measure these in circuit. That's often the case but sometimes you get lucky so it's worth a try. BTW R39 is 4.7K.
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  11. #46
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    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?
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  12. #47
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    On IC4 - sorry I was getting muddled with another thread where the PWM chip was bad. Ignore the remark.
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  13. #48
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    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.
    Last edited by DaedalusWren; 01-12-2017 at 04:20 AM.
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  14. #49
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    Quote Originally Posted by DaedalusWren View Post
    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.
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  15. #50
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    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.
    Last edited by DaedalusWren; 01-12-2017 at 08:57 AM.
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  16. #51
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    Quote Originally Posted by DaedalusWren View Post
    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.
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  17. #52
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    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?
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  18. #53
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    Quote Originally Posted by DaedalusWren View Post
    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.
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  19. #54
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    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.
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  20. #55
    Supporting Member The Dude's Avatar
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    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!
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    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
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  22. #57
    Supporting Member Jazz P Bass's Avatar
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    Quote Originally Posted by DaedalusWren View Post
    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

  23. #58
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    Thanks for the file Jazz.
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  24. #59
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    Quote Originally Posted by DaedalusWren View Post
    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.
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  25. #60
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    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.
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  26. #61
    Senior Member Enzo's Avatar
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    Look on the boards. The power supply and power amp boards will have some model number on them, like SPS1000 or HSA2400. Those are older models, but they act as examples. Then compare to your schematic.
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  27. #62
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    Dug out the iNuke

    I'm back. I got my NU3000DSP out of storage and opened it up to get board numbers. Well it seems there is only one combo board inside combining the PSU and Amp circuitry. I have taken pictures, and from a screen print on the board close to the mains, it mentions the different fuse ratings for the 3000 and the 1000. This leads me to believe that the NU1000DSP and the NU3000DSP share the same base board with different Amp transistors. The only board numbers I could find were ( PCB107071REVC_02 POAEJ/POAHO ). As far as I can remember, one channel is not working, I believe channel A. I will have to set it up and test it out again. Some pics will be attached. So, who might have a schematic for the NU1000DSP? Cheers.
    Attached Thumbnails Attached Thumbnails nu3000dsp-full-board.jpg   nu3000dsp-fusemap.jpg   nu3000dsp-model.jpg  
    Last edited by DaedalusWren; 01-24-2017 at 08:07 AM.
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  28. #63
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    Sorry don't have that schemo. It would be best to start a new thread - maybe a mod could move? My strategy in a case like this would be comparing signals between the working channel and the bad channel combined with a general idea of the architecture and using the datasheets for the various ICs.
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  29. #64
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    Yes, that sounds like the best way forward here. Tracing backwards from the output through the circuit. Best would probably be to split the sound from a signal generator to both inputs, would it not? And yes, I will start a new thread with this if it is not moved by a wonderful mod. Cheers.
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