SA-7800 idle current creep ?

Discussion in 'Pioneer Audio' started by Markoneswift, Jul 11, 2018.

  1. Markoneswift

    Markoneswift Quartz locked n ready to rock

    Messages:
    3,277
    Location:
    Aotearoa New Zealand
    Hello all. I have just started cleaning up and adjusting my free SA-7800 and I have a question.

    The service manual is very straight forward and I surprised to find the only adjustments I can check are those for idle current

    On measuring the voltages and setting them at the appropriate pot, I see the mV at the test pins is creeping around and not holding steady. Is this normal ? I'm only talking about a slow creeping from say 53 mV to around 55 in .1 increments so I assume the tiny voltages concerned are nothing to worry about, correct ?
     

     

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  2. Watthour

    Watthour Electron Rancher - JS3600

    Idle current will move with temperature change. It is a function of the forward voltage drop of the P-N junctions being affected by temperature. If the idle current varies several tines per second, we might be concerned about the reliability of the trimmer. Of course, adjustment needs to be made with no signal applied to the amplifier circuit.
     
  3. Markoneswift

    Markoneswift Quartz locked n ready to rock

    Messages:
    3,277
    Location:
    Aotearoa New Zealand
    Thanks that's pretty much confirmed what I was thinking. The creep is very slow in very small amounts so I'm not going to worry about it.

    There's seems to be a capacitor 'upgrade kit' available online consisting of a bunch of Nichicons. Wonder if its worthwhile giving that a go.
     
  4. Watthour

    Watthour Electron Rancher - JS3600

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