recapping sx-850 for my son

Discussion in 'Pioneer Audio' started by nackesww, Mar 22, 2018.

  1. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    149
    Location:
    Mamou, Louisiana
    Don't use the hold mode when checking voltage. You need to ohm out the 3 transistors and see if any of them are shorted, in particular Q2. Unplug the 850 and put your meter on ohms and check between the collector and emitter, collector and base, emitter and base, and tell me what it reads in ohms. That will tell you if it is shorted.
     

     

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  2. LesE

    LesE 110284 Subscriber

    Messages:
    773
    Location:
    Ontario, Canada
    mf could be millifarad. If so, 2.15mf = 2150uf.

    Les.
     
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  3. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    all transistors check out ok
     
  4. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    hmmm thats possible i guess. The old one was still good so ithrew that back in un til i get a new replacement. I did test the old one and it read 2180uf.
     
  5. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    149
    Location:
    Mamou, Louisiana
    Did you say that the emitter of Q4 is 17.35 volts? If so that Zener you put in there is not working. Are you sure you installed it correctly? Anode to emitter of Q4 and cathode to ground?
     
  6. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    do you think the transformer needs to be looked at? Q2 collector goes directly to D1,D3 anode so not sure how we would drop the voltage after that. I took some more measurements.
    pin no.
    16. 34.38 AC
    17. 47.01 DC
    18. 47 DC
    19. 34.36 AC
    22. 7.76AC
    23. 7.97AC
    24. 8.33AC
    25. 49.61AC
    26. 49.53 AC
    27. 21.1 AC
    28. 21.04 AC
     

     

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  7. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    149
    Location:
    Mamou, Louisiana
    Q2 drops the voltage through biasing. Please forget about the transformer and D1, D2, D3 and D4. I already know that is working! Please tell me the voltage on the emitter of Q4.
     
  8. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    Q4 emitter -17. I'll check the zeener diode.
    83 volts from cathode to Q4 emitter
    cathode to ground 65.8
     
  9. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    Q4 emitter to ground is 17.25
     
  10. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    I hope thats what you were asking for
     
  11. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    149
    Location:
    Mamou, Louisiana
    Cathode of the Zener should be 0 volts when measured to ground. That diodes Cathode MUST be soldered to ground, or it will not work! The emitter of Q4 is supposed to be 13.6 or so volts, not 17.35. Another thing, all voltages are referenced to ground.
     
    Last edited: Apr 8, 2018

     

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  12. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    my mistake the cathode of the zener is 0 to ground. I thought you were referring to D2.:(
     
  13. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    149
    Location:
    Mamou, Louisiana
    And you still have 17.35 volts on the emitter of Q4 to ground?
     
  14. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    -17.35 yes
     
  15. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    149
    Location:
    Mamou, Louisiana
    The Anode of the Zener diode is either not connected to the emitter of Q4, or it is not installed properly, or it is bad! OR, it is not the right diode!

    Until you correct this problem, there is not much more we can do! The emitter of Q4 MUST be 13 volts.
     
  16. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    I'll change it out with a new one. Glad I bought a kit so i would have plenty to spare.
     

     

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  17. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    149
    Location:
    Mamou, Louisiana
    Well now my concern is, why didn't the one you put in there work? Polarity is a must. Cathode to chassis ground and Anode to the emitter of Q4.
     
  18. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    The new zener brought voltage down to 12.74 on Q4 emitter. Thats odd, the old one tests ok. Oh well
     
  19. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    149
    Location:
    Mamou, Louisiana
    Well probably it was not connected or soldered well. What are the voltages at pins 13, 14 and 15 now?
     
  20. nackesww

    nackesww Member

    Messages:
    96
    Location:
    New Auburn, Wisconsin
    ................B............C..........E
    Q2 - 50.13.......-67.6......-49.54
    Q4 -13.45........-50.16.....-12.93
    Q6 -19.91.......-44.32......--17.44
     

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