Yamaha CR 2020 41Vdc on outputs!

Discussion in 'Solid State' started by Mid-Fi, Sep 12, 2017.

  1. Mid-Fi

    Mid-Fi AK Subscriber Subscriber

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    I did while I had the board out they are replaced as pictured.

    upload_2017-9-13_19-0-29.jpeg

    +230mv R1

    Curious if lifting R1 would allow the relay to close and Left channel to play.

    And yes confirmed +41 on both channels
     
  2. Mid-Fi

    Mid-Fi AK Subscriber Subscriber

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    No idea how to diode test. In or out of circuit. Will scan YT for video
     
  3. avionic

    avionic " Black Knights " Subscriber

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  4. mbz

    mbz AK Subscriber Subscriber

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    Plenty of good posts on how to diode test as per avionic above.
    I like this one from markthefixer who updated a graphic from echowars.
    Red/black refer to probe orientation.

    DiodeTest.JPG
     
  5. mbz

    mbz AK Subscriber Subscriber

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    Right In (yellow wire) is higher than LI, problem with right channel. TR611 and maybe TR612 are prime candidates, however certainly check outputs
    (TR613,4).

    If left channel dc offsec is below threshould then relay should activate. If this is just a solder connection then ok to try, but carefully secure
    this floating wire. If this is a wire wrap connection then don't tinker.
     
  6. Mid-Fi

    Mid-Fi AK Subscriber Subscriber

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    Gotcha. I'll dig in as the opportunity arises.
     
  7. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

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    Hi guys, this fine piece of Yamaha gear is under new ownership. (Thanks Mid-Fi!) Though I've always been fond of Pioneers, I feel Yamaha nailed it with this series. I've never worked on any Yamaha gear, and am a novice, as I've only repaired about a dozen pieces, in a variety of types. (Turntables, receivers, reel-to-reels, equalizer...) But they were all Pioneer. Not familiar (at this point) with Yamaha terminology nor the "Yamaha way" of doing things. That's not a criticism, just an observation from a rookie.

    Regardless of the gear, I don't know how to troubleshoot electronics. I can follow instructions, and don't jump all over the place. Can't read a schematic for crap, though.

    So where're we at? I've opened up the beast and gotten access to the main Circuit Boards--I think Yamaha refers to both boards as Main Circuit Board 1?

    I pulled TR611 and TR612 (1 from each board) and hit them with the diode test, they're all good. I then tested the outputs, TR613, TR614 (again, from both boards) and they all checked out good, too. (Testing done the six-way testing method.)

    I've left them out of the boards for now. When they go back in, I'll clean off the the old thermal grease and apply new. (Clean off old flux, etc)

    I'm not sure of the next step, and would gladly accept suggestions.

    Thanks,

    Jeff

    PS I have a copy of the Service Manual as well as the three service bulletins
     
  8. avionic

    avionic " Black Knights " Subscriber

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    What voltage are you seeing on the output transistor cases(collector). Should be around + and - 60vdc.
     
  9. avionic

    avionic " Black Knights " Subscriber

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  10. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

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    Ok, I'll put all the transistors back in. When I power it up and check the voltages, I'm assuming positive to the case collector, and negative to chassis ground?

    Thanks for that, avionic! I'll get those ordered.
     
  11. avionic

    avionic " Black Knights " Subscriber

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    Correct.
     
  12. avionic

    avionic " Black Knights " Subscriber

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    If the negative rail is missing to the amplifiers that will cause the positive rail to be present at the output -- ie DC offset
    The pos and neg. rails must be equal. ie +60 and -60vdc (ballpark)
     
  13. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

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    Ok, cleaning, new thermal grease, transistors back in. Decided to check my work with dim bulb, it lit bright, then quickly dimmed. Excellent.

    Put my DMM to work. I'm getting -59 vDC on both 554 outputs (the ones toward rear of unit) and +59 vDC on the 424 outputs. Does that mean my power supply is doing what it's supposed to?

    And I've ordered the resistors.

    fyi, one existing symptom, don't know if it plays a part or not, is none of the white lamps illuminate. (I haven't investigated these at all, but thought I should mention it)

    I do get a red power light that comes on.
     
  14. avionic

    avionic " Black Knights " Subscriber

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    That means the unregulated supply is working as it should.
     
  15. avionic

    avionic " Black Knights " Subscriber

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    Still getting 41 volts on the output ?
     
  16. avionic

    avionic " Black Knights " Subscriber

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    Post a photo of the top of the Electrolytic board showing the solder lugs and wires connected.
     
  17. avionic

    avionic " Black Knights " Subscriber

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    This board...
     

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  18. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

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    Sorry, where do I take that measurement?
     
  19. Oilmaster

    Oilmaster Ozzy Subscriber

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    The thing with the white light bulbs is that they are hooked up in "parallel-series", meaning that two sets of two lights in parallel are connected on series. A very twisted way to ensure same light intensity (current regulation). The weak point in that design is that if one bulb dies, than the parallel brother gets the full current of the other set in series and burns out quickly.....and then the entire chain is dead..... really shitty design.....

    In other words: you need to order 4 new light bulbs, and in theory you should match the bulbs that are in parallel, otherwise a different current runs through them and shortening the lifespan even more. I converted everything with warm white leds, 5 of them in series (which includes the dial pointer light) with a 220 ohm resistor, all fed from the VU-meter lighting terminal (hence no longer using the dedicated lighting supply terminal for the dial pointer)
     
  20. hertzdonut

    hertzdonut Press Play and Stand Back Subscriber

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    Ok, started digging in. The first thing I notice is loose wire. Loose as in not connected on one end. I don't know if a fragile connection gave way as I started to move the board that plugs into the cap board or what, but there it is. One end is connected to Pin E, the other end I have no idea where it's supposed to be.

    Moving on.

    I took some shots, let me know if I didn't get what you were after.
     

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