Quest QA3004 - suspected blown output stage

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  • Amraks
    Badcaps Veteran
    • Nov 2011
    • 725
    • Australia

    #1

    Quest QA3004 - suspected blown output stage

    First time really working on a amplifier.

    Symptoms where
    person plugged in on the outputs.
    4 output stage fuses died.
    They put in another set of fuses and only 2 on one side died this time.

    Upon my inspection I have found water on the side that killed the 2 fuses the second time.
    I have included pictures of little pool of water its hard to know how much water has been in this as I found some on a few mosfets as well.

    I am not sure if my in circuit transistor tester(jaycar or dicksmith) is capable of testing these transistors.
    as I have used it and they are all reading short on both channels.

    Desoldering one of the resistors from the base of transistor apparently make for easy testing the transistors.

    What should I be looking for when testing these?
    Attached Files
  • andy1
    New Member
    • Apr 2019
    • 9
    • USA

    #2
    Re: Quest QA3004 - suspected blown output stage

    You could try using a hair dryer and get rid of the moisture before powering up.

    Comment

    • Amraks
      Badcaps Veteran
      • Nov 2011
      • 725
      • Australia

      #3
      Re: Quest QA3004 - suspected blown output stage

      I will have to try that.
      I just hope they haven't switched it to bridge mode with a load under 8 OHMS
      as it says in the books it will blow the A side.

      Comment

      • Amraks
        Badcaps Veteran
        • Nov 2011
        • 725
        • Australia

        #4
        Re: Quest QA3004 - suspected blown output stage

        I am having a crack at this amp
        Found 2 Blown Transistors on the A Side
        Found 9 blown Transistors on the B Side

        Now my question is if I have cleared all these shorts would I adjust bias 1 side at a time
        So do A side first
        then B side

        would I need to turn down the bias first?
        Would I need more than 1 multimeter for negative and positive side to balance the bias?
        Last edited by Amraks; 11-16-2019, 06:51 AM.

        Comment

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