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Behringer PMP4000 half working

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  • Behringer PMP4000 half working

    Working on half dead Behringer PMP4000. Wondering if the fans are supposed to come on when the unit is powered on, or if they are thermostatically controlled. My reason for the inquiry is to deduce whether the PSU or amp board need to be changed. Tested out low voltage power to mixer board and all test out ok, the mixer lights all work fine and the board works fine with an external amp. The high voltage is not present for the amp board, but I hear that these switching PSU's can be tricky to diagnose as they require a load for them to actually switch into operating mode. With this in mind, I figure it can either be the amp board or the PSU. The fans seem to get powered from a winding on the same transformer as the hi voltage mains to the amp board, so if they are supposed to come on without thermostat, then can I safely assume the PSU is culprit. Does anyone know beyond a shadow of a doubt if the fans fire up on power-up? Is there something I might have to look at that I haven't thought of yet? Any help would be greatly appreciated. Thanks.
    Last edited by DaedalusWren; 12-16-2016, 09:40 PM.
    What light reveals that, which is hidden within the shadows of the mind?

  • #2
    Is there a separate PSU for low and high voltage sections? I find it hard to believe the PSU is sophisticated enough to shut down the voltage to the power amps yet leave the mixer running. I think a fault would shut down the whole PSU ?
    Originally posted by Enzo
    I have a sign in my shop that says, "Never think up reasons not to check something."


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    • #3
      I would think so too.
      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        The fans are powered by the Pos+ & Pos - buss.
        Which I can only assume is the high voltage rails.
        Attached Files

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        • #5
          Originally posted by Jazz P Bass View Post
          The fans are powered by the Pos+ & Pos - buss.
          Which I can only assume is the high voltage rails.
          Unfortunately, this is not the PSU from this unit. It is an SMPSU29 switching psu.
          Attached Files
          Last edited by DaedalusWren; 12-18-2016, 05:27 AM.
          What light reveals that, which is hidden within the shadows of the mind?

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          • #6
            Is it just the time of year, or are there really so little people here to help? Someone must have had some experience with this power supply.
            What light reveals that, which is hidden within the shadows of the mind?

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            • #7
              Y'know...there are many of us here who do little else but help people learn, bu tthis is primarily a guitar amp forum, so this mixer is not really the type of thing most here work on.

              Also, you only provided half the SMPS schematic.

              The SMPS has a low voltage circuit, making the 15v rails. But it also makes VCC for the HV supply control circuits. SO make sure VCC is being generated. D6, C12.

              Yes the PA can shut down the SMPS.

              Get VCC to the HV supply controller IC. Make sure the shutdown pin on IC4 is not low, shutdown is controlled by IC3.

              WARNING
              the SMPS is very dangerous to work on, please use an isolation transformer. The "ground" in all these control circuits is NOT chassis ground, it is the -170v from the rectified mains.
              Education is what you're left with after you have forgotten what you have learned.

              Comment


              • #8
                As Enzo said, you provided only half of the power supply schematic. This mixer has two power supplies (clearly visible when you open the enclosure), one for low power supply (+5V, +/-15V) and the other for the high power supply (power amp rails and fan supply). From what you write, the high power supply is not working. It may be due to its failure, or the power amp failure - you have to find out the reason for the failure.

                Mark

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                • #9
                  Originally posted by DaedalusWren View Post
                  Is it just the time of year, or are there really no little people here to help?
                  That is correct.
                  The little people are very busy at the north pole at this time of the year.
                  Originally posted by Enzo
                  I have a sign in my shop that says, "Never think up reasons not to check something."


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                  • #10
                    Is this the same supply?
                    BEHRINGER PMP6000 SCH Service Manual free download, schematics, eeprom, repair info for electronics
                    Originally posted by Enzo
                    I have a sign in my shop that says, "Never think up reasons not to check something."


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                    • #11
                      Yes, the 6000 and 4000 have the same SMPS.
                      Education is what you're left with after you have forgotten what you have learned.

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                      • #12
                        You need to do some probing. For a start what is the shutdown pin 10 of IC4 doing? Is the supply VH present? What about VCC? Can you disconnect the power amp from the power supply and see if it powers up - it might not regulate properly but you should get something.
                        Experience is something you get, just after you really needed it.

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                        • #13
                          Thanks for the starting point to check. Yes the 4000 and 6000 have the same PSU. I will test out the points suggested and get back to you. As it sits now. With the amp disconnected it remains in the same state. The low power voltage is present but nothing to the high voltage amp supply pins or fans. Will get back with the other points. Thank you all for your assistance.
                          What light reveals that, which is hidden within the shadows of the mind?

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                          • #14
                            If "VCC" doesn't come from the LV supply, then nothing will happen in the HV circuits.
                            Education is what you're left with after you have forgotten what you have learned.

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                            • #15
                              Ok, did some probing. First off, I would like to thank all who have added to the thread and given me information and points to probe. I understand basics of electronics, know how to probe and could probably diagnose this PSU if it were a basic bridge rectifier, capacitors and transformer. The Switching ones are Greek to me, so thanks again.

                              The probing of D6 and C12 provided me with 15.2vdc
                              IC2 pin 7 or VH is 7.5vdc
                              IC4 pin 10 or Shutdown is 3.7VDC
                              IC4 pin 15 or VCC 15.2vdc

                              Hope this helps.

                              (edit) After doing some looking around and finding the spec sheet for KA3525A, which is IC4. The Shutdown threshold voltage Vth=1.3vdc Typ. or 1.7vdc Max. So if I am reading these specs right. The voltage at pin 10 being 3.7vdc should be sufficient. If I am associating the right values to the right pin.
                              Last edited by DaedalusWren; 12-23-2016, 01:51 AM.
                              What light reveals that, which is hidden within the shadows of the mind?

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