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Eight Deluxe power supply board issues

Discussion in 'Exclusively Sansui' started by bobok7787, Oct 10, 2018.

  1. bobok7787

    bobok7787 New Member

    Messages:
    19
    Greetings!
    I recently started having problems with my 8D, the relay intermittently kicks out and quickly back in at seemingly random times. I've been meaning to re-cap this receiver for quite some time so I went ahead and did so (all except tuner boards), hoping it would alleviate the issue (it didn't).

    I found a thread with a similar issue from about six years ago, but it seemed to go unresolved: http://www.audiokarma.org/forums/index.php?threads/intermittent-relay-speaker-cutout.477880/

    Adding to this, maybe related or not, but after the recap and subsequent relay problems I was poking around with a wooden stick to see if I could re-create the relay issue and I noticed a few components on the F-1201 power supply board were very hot to the touch (hot enough to burn my finger if I left it on there).

    The hot components were D001, D002, R001, R003, TR001, and TR002. I check voltage on incoming 35V OA and OB points and noticed it was a tad high at 39 volts. Would that be enough to overheat the components that much?

    In addition, I pulled the affected diodes, resistors, and transistors and all tested good and within spec. I also checked R004, R014, and TR003 and again, all good and within spec.

    Am I heading in the right direction by testing the surrounding components until I find an issue, or would the problem lie further downstream somewhere on the 24V and 14V rails? I haven't checked these output voltages yet, I will tonight after I've reassembled the pulled components. Any advice is much appreciated.

    Thanks for reading!
     

     

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  2. bobok7787

    bobok7787 New Member

    Messages:
    19
    Rechecked a few voltages after reassembly:
    OA - 38.80 V
    OB - 38.75 V

    OD - 13.92 V
    OE - 25.41 V

    Components are still very hot to the touch.
     
  3. dr*audio

    dr*audio Fish fingers and custard! Subscriber

    Messages:
    18,774
    Location:
    Cleveland, Ohio
    When the protection relay kicks out, the first thing to look at is the DC voltage on the speaker terminals (measured with the relay engaged and volume at 0. If this is close to 0V, within +/- 20mV, the problem is on the protection board. You already replaced the caps so the next suspect is the driver transistor for the relay. Often the HFE drops and they don't engage the relay.
     
  4. Robisme

    Robisme Sansui Enthusiast Subscriber

    Messages:
    11,783
    Location:
    Martinez California
    Do you hear a pop in the speakers when it trips into protection?

    Rob
     

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