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CR-2020 - Smoking Resistor

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

  1. zaskarx

    zaskarx Member

    Messages:
    95
    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:
    43,684
    Location:
    Fort Dodge, Iowa
    While you are in there. Pull and test TR612 driver as well. The green one with the little heatsink.
     
  3. zaskarx

    zaskarx Member

    Messages:
    95
    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:
    43,684
    Location:
    Fort Dodge, Iowa
    No
     
  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,684
    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

    Messages:
    43,684
    Location:
    Fort Dodge, Iowa
    R627 and R628 and the final output emitter resistors R631 and R632.
     

     

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  7. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,684
    Location:
    Fort Dodge, Iowa
    Yamaha " chernobyl"
     
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  8. zaskarx

    zaskarx Member

    Messages:
    95
    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.
     
  9. zaskarx

    zaskarx Member

    Messages:
    95
    Location:
    Phoenix, AZ
    Making progress, the new parts are in, passed the DBT test and no smoke under full power. No relay click and I don't seem to have an idle current on the right board, it is stuck at .7mv no matter what I do to the pot. The board is receiving ~112v from the power supply. Left channel is fine and solid at ~10mv after a little adjustment.
     

    Attached Files:

  10. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,684
    Location:
    Fort Dodge, Iowa
    +56vdc and -56vdc you mean. Measured between E and +B and E and -B . Are both of those fuses still serviceable?
    Did you check the ....
    And ....
     
  11. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,684
    Location:
    Fort Dodge, Iowa
    Were these verified out of circuit?
     

     

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  12. zaskarx

    zaskarx Member

    Messages:
    95
    Location:
    Phoenix, AZ
    Yes, that's correct, just rechecked and it is closer to +59vdc and -59vdc. Fuses are OK, as are all resistors besides FR601, which was bad, I replaced all of the above mentioned resistors and the diode out of an abundance of caution.
     
  13. zaskarx

    zaskarx Member

    Messages:
    95
    Location:
    Phoenix, AZ
    Yes, both transistors were verified out of circuit and replaced.
     
  14. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,684
    Location:
    Fort Dodge, Iowa
    On the bad channel measure the DC voltage between the O and E lugs on the top edge of the circuit board. Do not short those two connections together. Or you will be buying more output transistors.
     
  15. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,684
    Location:
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    What did you replace R627 and 628 with ?
     
  16. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,684
    Location:
    Fort Dodge, Iowa
    On the bad channel measure the base voltages of TR611 and 612.
     

     

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  17. zaskarx

    zaskarx Member

    Messages:
    95
    Location:
    Phoenix, AZ
    O-E - 41.3v
    TR611 - 42.4v
    TR612 - 42v

    Replacements:
    R627, R628 - ERX-1SJ4R7
    R631, R632 - PAC500004707FAC000
    Fried resistor (can't remember the number) - CFM12JT470R
    FR601 - ERG-1SJ680
    D607 - 1N4148

    I also replaced TR608 with KSC1815YTA since the original has a reputation for being noisy

    Thanks again for the help, much appreciated!
     
    Last edited: Sep 24, 2018
  18. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,684
    Location:
    Fort Dodge, Iowa
    Did it get installed correctly?Rounded side against the heatsink.
     
  19. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,684
    Location:
    Fort Dodge, Iowa
    OH oh shaggy.. That is about 41 volts to high. Were they both positive or negative with reference to ground ?
     
  20. zaskarx

    zaskarx Member

    Messages:
    95
    Location:
    Phoenix, AZ
    I sure hope so! The rounded back rests against the large aluminum heatsink for the outputs, not the tab that holds in place on the PCB.

    The measurements were both positive, I grounded the negative lead of my multimeter to the chassis.
     

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