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Yamaha CR-600 Offset Issue

Discussion in 'Yamaha' started by ivandezande, Oct 21, 2018.

  1. ivandezande

    ivandezande Super Member

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    I think I'm cursed from working on CR's, second one with strange issues. This guy had a blown bridge rectifier and everything else seemed to be fine.

    On the driver board I replaced the caps, the bias transistors Q707,8, Q705,6 as they were Sony's that I've had problem with, and trimmers.

    It biases perfectly, but when I measure for offset between test points, it looks to be almost negative 30V on each output! I checked for transistor installation, but 7 and 8 are fine if the SM is right and it biases so not worried about 5,6 and they are supposedly in correctly.

    I'm seeing -37V on the collectors of 707,8 which should be -1V. Emitters are -27V and -37 respectively. Bases are correct at 37V.
    On the input pair, I'm seeing 37V on both collectors which isn't right.
     
    Last edited: Oct 21, 2018

     

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  2. avionic

    avionic " Black Knights " Subscriber

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    Check F801.
     
  3. ivandezande

    ivandezande Super Member

    Messages:
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    Looks ok at 4.4 ohms.
     
  4. avionic

    avionic " Black Knights " Subscriber

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    Are you seeing +37.5vdc at the fuse?
     
  5. ivandezande

    ivandezande Super Member

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    Like the fuse resistor? 21.5V there. Seeing 38V on the main fused rails.
     
  6. avionic

    avionic " Black Knights " Subscriber

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  7. avionic

    avionic " Black Knights " Subscriber

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    What test points? TP-3 and TP-5?
     
  8. ivandezande

    ivandezande Super Member

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    Yup! And 1 & 3.
     
  9. avionic

    avionic " Black Knights " Subscriber

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    1 & 3 / 2 & 4 are bias TP's.
    3 & 5 / 4 & 6 are offset TP's
     
  10. ivandezande

    ivandezande Super Member

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    My bad, I did mean 3,5 4,6. Looked at the SM again too fast.
    Bias sets fine reading from 1,3 and 2,4.
     
  11. avionic

    avionic " Black Knights " Subscriber

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    So your seeing damn near rail on both channels at the outputs?
     

     

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  12. ivandezande

    ivandezande Super Member

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    Yessir. But the outputs aren't shorted. I've had this happen when I put in a transistor backwards before but I dang sure I didn't this time.
     
  13. avionic

    avionic " Black Knights " Subscriber

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    What voltages are you seeing around TR707 and 708?
     
  14. avionic

    avionic " Black Knights " Subscriber

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    Don't sir me.. I work for a living.:D
     
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  15. ivandezande

    ivandezande Super Member

    Messages:
    1,775
    Location:
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    I'm seeing -37V on the collectors of 707,8 which should be -1V. Emitters are -27V and -37 respectively. Bases are correct at 37V.
    On the input pair, I'm seeing 37V on both collectors which isn't right.
     
  16. avionic

    avionic " Black Knights " Subscriber

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    + or - 37?
     

     

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  17. ivandezande

    ivandezande Super Member

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    Negative.
     
  18. avionic

    avionic " Black Knights " Subscriber

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    -37 vdc is correct for the collectors of the LTP.
     
  19. avionic

    avionic " Black Knights " Subscriber

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    What did you replace the TR 707 and 708 with? KSC1845?
     
  20. ivandezande

    ivandezande Super Member

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    1,775
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    KSC2690
     

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