Restoring SX-3800 - From Power supply , moving to Amp section

Discussion in 'Pioneer Audio' started by John Hale, Nov 14, 2017.

  1. John Hale

    John Hale New Member

    Messages:
    23
    Hello all - I am declaring victory on the pwer supply (see thread " Restoring SX 3800... I have a few questions"). I thought I should start another thread so readers could differentiate the lines of effort. I have re-transistored (if that is a thing), re-capped and tested ALL resistors and diodes with one leg lifted. I have connected the Amp board to power supply (amp pins 1,2,6,7 and the plug ins at 29,30,31 and 35,36,37). I did NOT attach final output transistors.

    Status: brought up on variac. no explosions or Hot components (yippee). All the higher voltage test points (47, 45.7, -45.7, etc... test pretty well. However all the low voltage point are not correct :

    Q104 = - 8ish , should be 0
    Q104= -16ish, should be .7
    Also mirrored on the other side

    And all other subsequent Lower voltage points all reading in the negative teens rather than the required .7 or 1.2 volts.

    Can you give me a starting point? turning VR1 and VR2 potts had influence on Q104 but in no way could overcome that much variance.

    All input voltages from PS are within spec.

    I appreciate ya'll
    John
     
  2. John Hale

    John Hale New Member

    Messages:
    23
    Any takers?
     
  3. John Hale

    John Hale New Member

    Messages:
    23
    well folks - I am at my wits end. I was real optimistic when I got the power supply running, but the amp is driving ( ha get it) me crazy. I continue to chase some negative voltage coming from somewhere ( hate to be so vague) but i have traced the schematics , tested seemingly hundreds of components.... And I cannot find a "smoking gun". seems like I truck down a path, just seeing if I can make an impact on this -11V to -16V reading on all the places where ther should be + .7 v or +1.2V. The relay never kicks in (obviously).

    Please help ( and thank you in advance) . I have tried to narrow things but , nothing seems to effect the readings. I have worked for two weeks on this, I'm not the wicked smartest but I am no dummy either. I am going to give this one more day, then I'm going to pack it up and move on to a Marantz re-build.

    I feel terrible about my progress (or lack thereof) but I might have to get allot smarter before I can concur this NSA amp.

    I don't think I keyed any interest in a reply thus far, I would be happy to elaborate on details if that would generate some interest.

    Thank You
    John
     

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