1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

CR420/CR66ll Lights

Discussion in 'Yamaha' started by Fhamre, Aug 29, 2017.

  1. Fhamre

    Fhamre AK Subscriber Subscriber

    Picked up a nice little CR66ll. Needed a little attention.
    Looking at some great older posts I repaired a very stiff tuning shaft. Replaced the lights with LEDs.
    I found the DC offset to be about -95mv /channel.
    So I put a 1k trimmer in place of R407 and R408.That allowed me to get to 0mv easily.
    So while I was patting myself on the back I noticed that I no longer had my lights. Was a bit of work to do a nice job putting them in. But I have since taken them out and checked each one,again. No luck.
    I am getting 39V at L1,L2,L4. 6V at L3.
    Any suggestions?

    420.PNG 420a.PNG
     

     

    Please register to disable this ad.

  2. Roboturner91

    Roboturner91 AK Subscriber Subscriber

    Messages:
    1,127
    Location:
    SW Indiana
    This probably isn't the technical response you are looking for, but I don't have that expertise...

    However I do remember somebody here telling me when I had my CR-420, that the lighting circuit was really sensitive to tapping around in there and bulbs would blow out for no apparent reason. I believed it after going in to tighten up the tuning string and suddenly all the lights were dead. I put new bulbs in and it was fine after that, but I was dealing with regular incandescent bulbs and not LEDs.
     
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    Did you check F503 ?
     
  4. Fhamre

    Fhamre AK Subscriber Subscriber

    Yes !
     
  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    What kind of voltage are you seeing from L1 to L4 ?
     
  6. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    Wired in series. If one goes they all go.
     

     

    Please register to disable this ad.

  7. Fhamre

    Fhamre AK Subscriber Subscriber

    We talking DC or AC? 2.5VAC, 0V DC
     
  8. Fhamre

    Fhamre AK Subscriber Subscriber

    Yes I am aware they are in series. Thx. Strange that the three LEDs worked fine until it seems I addressed the DC offset. Although that could be just a coincidence.
     
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    I would have been looking for a DC voltage there.
     
  10. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    I think I see whats going on. To get your DC offset under control.Your probably going to have to replace the long tailed pairs.(Diff pair) TR403/405 or TR404/406 with Hfe matched transistors. Any who, the trimmers are loading down the regulated power supply.
     
  11. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    Or you have a power supply issue.:idea:
     

     

    Please register to disable this ad.

  12. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    Have you recapped the power supply circuit yet ?
     
  13. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    Check R501 180Ω 5 watt'er. So says the schematic.
     
  14. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    I would have been expecting around 35-36 volts DC.
     
  15. Fhamre

    Fhamre AK Subscriber Subscriber

    The unit has been performing fine. It was a freebie that I plan to pass on to my daughters room mate whom expressed interest in a vintage piece. The gist, I wasn't planning to recap it if I didn't need to.
    What would be good subs for those transistors?
    Maybe I could try increasing the DC offset to say 35mv or so.
     
  16. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    Did you use individual dropping resistors with your LED's ? What Ω value and wattage ?
     

     

    Please register to disable this ad.

  17. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    See what happens.
     
  18. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    Each LED would be required to drop 11 - 12 vdc.
     
  19. Fhamre

    Fhamre AK Subscriber Subscriber

    The 180 ohm tests fine!
     
  20. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,740
    Location:
    Fort Dodge, Iowa
    Damn I was hoping that was it.
     

Share This Page