CR-2020 - Smoking Resistor

Discussion in 'Yamaha' started by zaskarx, Sep 13, 2018.

  1. zaskarx

    zaskarx Member

    Messages:
    61
    Location:
    Phoenix, AZ
    I picked up a non-functioning CR-2020, it looked great outside but ended up being somewhat of a basket case inside, likely due to heavy use. The main filter cap board had a number of traces that had been roasted off of the PCB and some not so happy caps, transistors and resistors. I replaced all of the bad components (including all electrolytic caps) and performed the service bulletin updates. I made SURE to orient the incorrectly marked cap correctly on this board.

    Figuring the rest of the caps were likely in sorry shape, I decided to recap the entire receiver and give it a thorough cleaning. I finally fired it up yesterday on the DBT, everything seemed OK so I plugged it directly in. It was fine for a few minutes, but when I started adjusting the idle current, a resistor on the right output board went up in smoke. It is the 470 ohm resistor right above diode D607, pics are attached.

    I'm hoping this doesn't mean that the output transistors are shot, I am planning on taking them out of circuit this evening and testing but would appreciate any guidance/advice from those who are more familiar with the CR-2020 on what else to inspect/check. I can't imagine it is just an isolated bad resistor. Thanks!
     

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  2. avionic

    avionic " Black Knights " Subscriber

    Messages:
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    While you are in there. Pull and test TR612 driver as well. The green one with the little heatsink.
     
  3. zaskarx

    zaskarx Member

    Messages:
    61
    Location:
    Phoenix, AZ
    Thanks for the advice, both outputs are shorted as are TR612 and TR611, I wonder what happened to this poor receiver.

    Here are the replacements I'm considering, would appreciate any thoughts:

    2SB554/2SD424 > MJ21193G/MJ21194G - Should I replace the outputs in the left channel as well so that they match? The left outputs tested OK.

    C1624/A814 > MJE15032G/MJE15033G

    Anything else that you'd recommend testing/replacing? Parts are cheap so I'd rather be safe than sorry!





     
  4. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,159
    Location:
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    No
     
  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,159
    Location:
    Fort Dodge, Iowa
    Check the fusible resistor FR601 (68Ω/100ma) and D607 between the emitters of TR611 and 612.

    FR601-- 68Ω/1 watt flameproof
     
    Last edited: Sep 13, 2018
  6. avionic

    avionic " Black Knights " Subscriber

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    Location:
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    R627 and R628 and the final output emitter resistors R631 and R632.
     

     

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  7. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,159
    Location:
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    Yamaha " chernobyl"
     
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  8. zaskarx

    zaskarx Member

    Messages:
    61
    Location:
    Phoenix, AZ
    Thank you Avionic, you are a wealth of knowledge! I'll check and replace the parts and report back. May take me a week or so since I have to order the parts from Mouser or Digikey.
     

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