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peavey XR8600 channel issue 90v on speaker out

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  • peavey XR8600 channel issue 90v on speaker out

    Hello all
    This one is doing my head in
    It came in dead. Blown fuse replaced fuse and under Lamp limiter i can see excess current draw.
    Removed the power leads to Power amp and found one channel is the cause.
    with the bad channel disconnected all working correctly on the other channel

    Located a s/c bridge replaced tested still the same
    I saw a couple of the 0.22R 5watt to be ok but dis coloured, where the others were not.
    So as i have all the transistors in stock i decided to to blanket change of them
    4 x 2sc5200
    4 x 2sa1943
    2 x 2sa1837
    2x 2sc4793
    All like for like and all new

    on start up excess current draw through the lamp limiter , then i spotted it The triac on speaker board was short
    Could of kicked myself , anyway replaced it , with no speaker load, there is 90+v on speaker out with no excess current draw

    These are difficult to work on at the best of times, so before i removed the transformer so i can test on the bench and work on it easier So i have gone over the board trying to do some cold checks comparing working to non working

    I have found nothing,
    Im not so hot on the ss amps. sadly .... But i have found one thing which i think is nothing but i would like to ask

    when i use the DMM on the output transistors i have different reading from

    Base to emitter on Q220 -Q219 23 ohms ( R279 and R403 ) ( 47R ok
    Base to emitter on Q120 -Q119 6 ohms ( working channel )
    I have checked all 0.22r and all diodes and other semi's that can be tested
    all the other reading from channel to channel are the same
    LT +/- Rails are there
    Ht + /- are present
    peavey_xr8600_sch.pdfany help on this would be grateful

  • #2
    + 90 Vdc on the output?
    Seeing that this is a 'rail switching' output design it would appear that you have at least two issues.
    1: the positve rail high voltage is on all of the time (Q100)
    2: your negative rail is not conducting.


    • #3
      Ok Its been a week or so since i last looked at this.
      Ive retested and this is what i got

      I know i said i had 90v on the speaker outs but on this retest this morning i have
      i have -35V on speaker outs.

      voltages on faulty channel are as follows all checked while on lamp limiter

      Q201 - B+97v C +35v E+97v
      Q202 - B+97v C +35v E+97v
      Q210 B +35v C+35v E+35v
      Q207 B +35v C+35v E+35v

      Q216 B +35V C-35v E +35v
      Q214 B +35V C-35v E +35v
      Q219 B - 97v C -35v E -97v
      Q220 B - 97v C -35v E -97v

      Q200 B +27 C +97v E +35v
      Q208 +35 all pins
      Q221 B - 35v C-97v E -35v
      Q215 B -35v all pins

      R 252 but has got a little hot, was not burnt out but replaced it anyway
      15+ /15- present and 25V +/-
      as stated before all the output transistors and 4 drivers ( all of the above ) been changed for new and like for like
      all have been checked that they are ok and correct

      I'm a little stuck for idea's at present
      Mr A