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GK no output burning resistor

Discussion in 'Amps and Cabs [BG]' started by lowellg, Mar 12, 2008.


  1. lowellg

    lowellg

    Mar 12, 2008
    hello all,
    i've got a 1001rb that came to me w/ no output. I managed to trace some audio paths, replaced a few parts and got some sound, but then it quickly died and I saw a resistor (R27) go up in smoke. I cannot figure out what's causing it. I replaced the transistors that are schematically wired to that resistor and it still fries. When testing the output xistors they all test kind of weird... that is they do not pass the traditional "diode" tests. Anyone know if that sound like it's the problem or should I remove them and test 'em.
     
  2. jrfrond

    jrfrond

    Jul 11, 2006
    NYC
    Tech Director, dBm Pro Audio Services, New York
    DC-coupled solid-state amps can be an enigma to people who are not familiar with their topography, operation and troubleshooting procedures. Because many stages are coupled directly to each other and no isolated through capacitors to block DC (hence the term "DC-coupled"), a problem upstream can cause failures downstream.

    You need to check the output transistors OUT-OF-CIRCUIT, because the peripheral components required for biasing will conduct with in-circuit static testing methods.

    Do you power it up slowly on a variac to see if it is doing a soft or hard current draw? If not, you are going to shoot yourself in the foot many times over replacing damaged components. You might want to call in a tech who is a SS whiz.
     

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