HH Electronic MX1200 Power Amplifier Fuse shorted

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  • 9w2tzw
    Member
    • May 2013
    • 14
    • Malaysia

    #1

    HH Electronic MX1200 Power Amplifier Fuse shorted

    Hi,

    Currently i got one unit of HH Electronic MX1200 power amplifier.it can be turned on without any indicator of protect LED being in ON state.But the problem is, it can't detect any input signal.So, when i open the cover, i noticed that the 1A fuse of both channel keep blown even i had replaced it.Original owner said it the power amp has gone down since he "misshorted" the + and - terminal of the speaker.Any idea? by the way i had attached the schematic for reference.
    It uses 10 pair of BUZ901 and BUZ906 Mosfet transistor.total 20 for both channel.













    Attached Files
    Learn a Little but Often,
    Practice Makes Perfect,
    Repetition is the Key of Success,
  • Th3_uN1Qu3
    Believe in
    • Jul 2010
    • 6031
    • Romania

    #2
    Re: HH Electronic MX1200 Power Amplifier Fuse shorted

    The 1A fuse is for the 70v rail as per the schematic. Measure between either end of the fuse holder and ground. You'll find one of the ends is shorted. Then it's a matter of tracing thru the circuit and see which part has caused the short.

    Also, have you checked the output transistors already? If they are blown, it's gonna be an expensive repair.

    A word of warning: This power amplifier uses high voltage rails and has large capacitors. Make sure the main capacitors are discharged prior to attempting any work on this unit, otherwise serious damage to you, your tools, or the amplifier itself may occur.

    If the caps still show over 30 volts after several minutes after unplugging the unit, use a regular mains voltage lightbulb to discharge them.
    Last edited by Th3_uN1Qu3; 05-27-2013, 10:15 PM.
    Originally posted by PeteS in CA
    Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
    A working TV? How boring!

    Comment

    • 9w2tzw
      Member
      • May 2013
      • 14
      • Malaysia

      #3
      Re: HH Electronic MX1200 Power Amplifier Fuse shorted

      Originally posted by Th3_uN1Qu3
      The 1A fuse is for the 70v rail as per the schematic. Measure between either end of the fuse holder and ground. You'll find one of the ends is shorted. Then it's a matter of tracing thru the circuit and see which part has caused the short.

      Also, have you checked the output transistors already? If they are blown, it's gonna be an expensive repair.

      A word of warning: This power amplifier uses high voltage rails and has large capacitors. Make sure the main capacitors are discharged prior to attempting any work on this unit, otherwise serious damage to you, your tools, or the amplifier itself may occur.

      If the caps still show over 30 volts after several minutes after unplugging the unit, use a regular mains voltage lightbulb to discharge them.

      i had 2 times replacing the fuse.and they both got blown after i powered on the unit.

      thanks for reminder, can i use 82 ohm 5 watt resistor to discharge the capacitor?for smaller capacitor, i use this method to discharge them.

      i still dont know the exact ways to test the mosfet transistor.any guide?
      Learn a Little but Often,
      Practice Makes Perfect,
      Repetition is the Key of Success,

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #4
        Re: HH Electronic MX1200 Power Amplifier Fuse shorted

        Did you check the 4 1n4007 D40~D43 to see if they are shorted out?
        If the MOSFETs shorted out the fuses FS1~FS4 will blow also.
        Never stop learning
        Basic LCD TV and Monitor troubleshooting guides.
        http://www.badcaps.net/forum/showthr...956#post305956

        Voltage Regulator (LDO) testing:
        http://www.badcaps.net/forum/showthr...999#post300999

        Inverter testing using old CFL:
        http://www.badcaps.net/forum/showthr...er+testing+cfl

        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
        http://s807.photobucket.com/user/budm/library/

        TV Factory reset codes listing:
        http://www.badcaps.net/forum/showthread.php?t=24809

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #5
          Re: HH Electronic MX1200 Power Amplifier Fuse shorted

          Did you check the 4 1n4007 D40~D43 to see if they are shorted out?
          If the MOSFETs shorted out the fuses FS1~FS4 will blow also.
          Never stop learning
          Basic LCD TV and Monitor troubleshooting guides.
          http://www.badcaps.net/forum/showthr...956#post305956

          Voltage Regulator (LDO) testing:
          http://www.badcaps.net/forum/showthr...999#post300999

          Inverter testing using old CFL:
          http://www.badcaps.net/forum/showthr...er+testing+cfl

          Tear down pictures : Hit the ">" Show Albums and stories" on the left side
          http://s807.photobucket.com/user/budm/library/

          TV Factory reset codes listing:
          http://www.badcaps.net/forum/showthread.php?t=24809

          Comment

          • 9w2tzw
            Member
            • May 2013
            • 14
            • Malaysia

            #6
            Re: HH Electronic MX1200 Power Amplifier Fuse shorted

            Originally posted by budm
            Did you check the 4 1n4007 D40~D43 to see if they are shorted out?
            If the MOSFETs shorted out the fuses FS1~FS4 will blow also.
            D40-D43 i had checked and they just doing fine.

            How to tests out the MOSFETs shorted or not? Thanks for reply
            Learn a Little but Often,
            Practice Makes Perfect,
            Repetition is the Key of Success,

            Comment

            • rievax_60
              Badcaps Veteran
              • May 2012
              • 897
              • australia

              #7
              Re: HH Electronic MX1200 Power Amplifier Fuse shorted

              Originally posted by 9w2tzw
              D40-D43 i had checked and they just doing fine.

              How to tests out the MOSFETs shorted or not? Thanks for reply
              There is no reason to suspect the MOSFETs at this stage. Are there shorts to 0v on the VS2 rails?

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #8
                Re: HH Electronic MX1200 Power Amplifier Fuse shorted

                Then check the resistance reading on the output of the D40~D43 (full bridge setup) output to see if they are feeding shorted loads. You have shorted circuits that are causing the fuses to blow.
                "D40-D43 i had checked and they just doing fine" What are the readings?
                You are using Time Delayed fuses, right?
                Never stop learning
                Basic LCD TV and Monitor troubleshooting guides.
                http://www.badcaps.net/forum/showthr...956#post305956

                Voltage Regulator (LDO) testing:
                http://www.badcaps.net/forum/showthr...999#post300999

                Inverter testing using old CFL:
                http://www.badcaps.net/forum/showthr...er+testing+cfl

                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                http://s807.photobucket.com/user/budm/library/

                TV Factory reset codes listing:
                http://www.badcaps.net/forum/showthread.php?t=24809

                Comment

                • 9w2tzw
                  Member
                  • May 2013
                  • 14
                  • Malaysia

                  #9
                  Re: HH Electronic MX1200 Power Amplifier Fuse shorted

                  Originally posted by budm
                  Then check the resistance reading on the output of the D40~D43 (full bridge setup) output to see if they are feeding shorted loads. You have shorted circuits that are causing the fuses to blow.
                  "D40-D43 i had checked and they just doing fine" What are the readings?
                  You are using Time Delayed fuses, right?
                  I cannot managed to get reading at ON State since i am not using time delayed fuses.I just use normal 1A fuses since at my area are hardly enough to get this type of fuses.During OFF state, i managed to get 0.45 /0.47 V at all diodes , D40-D43.
                  Learn a Little but Often,
                  Practice Makes Perfect,
                  Repetition is the Key of Success,

                  Comment

                  • 9w2tzw
                    Member
                    • May 2013
                    • 14
                    • Malaysia

                    #10
                    Re: HH Electronic MX1200 Power Amplifier Fuse shorted

                    any helps?
                    Learn a Little but Often,
                    Practice Makes Perfect,
                    Repetition is the Key of Success,

                    Comment

                    • ben7
                      Capaholic
                      • Jan 2011
                      • 4059
                      • USA

                      #11
                      Re: HH Electronic MX1200 Power Amplifier Fuse shorted

                      Originally posted by 9w2tzw
                      any helps?
                      Check transistors T3, T4, T5, T8, T9, and T10 for shorts (desolder them from the board if you aren't sure if they are shorted or not, then measure them)
                      I think it's highly likely that at least one of them will be shorted out.
                      Muh-soggy-knee

                      Comment

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