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electrovoice_zlx_15p up in smoke

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    #1

    electrovoice_zlx_15p up in smoke

    one of electrovoice speaker stopped working the other day pulled it apart and found a whole section burnt up. replaced q1(mosfet) and a bunch of resistors around it. turned it on and it worked all voltages are there (+12 +15 -15) but then it started smoking again in a different area resistors R57 and R37. cant find anything else shorted but if i replace those burnt resistors they just get smoking hot and burn not sure why. added the schematic with whats bin done any help would be appreciated about to throw in the towel on this one
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    #2
    Re: electrovoice_zlx_15p up in smoke

    Check the gate drives, maybe one is stuck on. What is VCC doing on the 3845? If the FET was totally short on all pins, it dumped full power to the gate drive.

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      #3
      Re: electrovoice_zlx_15p up in smoke

      finally had time to look at this again
      the 3845 vcc was 8.3vdc

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        #4
        Re: electrovoice_zlx_15p up in smoke

        I repaired two of these with similar problems a few months ago.

        As well as replacing all the burned resistors & Q1 I also checked all components around the TL3845 and ended up replacing:

        I2 = Gate driver IC TL3845
        R62 - R71 = 1ohm resistors (replaced with single 3W 0.1ohm)
        Q1 = Mosfet 17N80C3 replaced with Toshiba TK31E60X,S1X
        R26 = 100ohm
        C48 = 100nF
        R120 = 180ohm fusible
        C49 = 0.1uF
        R28 = 150ohm
        R100 = 100ohm
        R121 = 680ohm
        D10 = Bat54 (replaced with Bat54C)
        Q8 = 6B = BC817 (2N3904)

        One also had problems on the pre-amp board that was sorted with some new MC33178 op-amps and a new gain pot.

        Both speakers back in service again ... one last thing to watch for is I found that one of the TDA8953 woofer amp chips was not making good contact with the raised heatsink platform for it (check with a torch from several angles when bolted down) ... I sorted this by replacing the original 1mm thermal pad with a 2mm pad.

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          #5
          Re: electrovoice_zlx_15p up in smoke

          Finely got the TL3845 in mail and that fixed it, stopped R57 and R37 from burning up.

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            #6
            Re: electrovoice_zlx_15p up in smoke

            Congrats! Another device saved from the bin!

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