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Yamaha R-V905 Won't power up

Discussion in 'Electronic Repair' started by Jakthehammer, Feb 16, 2008.

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  1. Jakthehammer

    Jakthehammer Guest

    Open up, check your power transistor/mosfet temperature after it power off, if hot then it proofs your thermo cutoff is working. Next figure what causes it to overheat.
  2. ICESoft

    ICESoft Guest

    Been working on this unit off and on for a while. It will power on for
    about 1/2 second then power right back off. History on this unit is that
    for a while it started to power off on its own with no rhyme or reason, it
    progressively got worse to the point that it wouldn't power up. Display
    just barely appears before the unit turns back off.

    I've checked the output transistors, they tested ok, also checked supply
    voltages, they appear good as well. I also resoldered any suspect solder
    joints I could find, still no dice. I don't have a full manual to work by,
    just some schematics for it.

    Looking for a kick in the right direction...

    Benjamin Jennings

    Posted via TITANnews - Uncensored Newsgroups Access-=Every Newsgroup - Anonymous, UNCENSORED, BROADBAND Downloads=-
  3. N Cook

    N Cook Guest

    As the display goes out , is it a switch mode power supply ?
  4. Arfa Daily

    Arfa Daily Guest

    Many of the Yammies use some 4 pin regulator ICs. They are common failures.
    Usually the +5v ones, type PQ05RD11, and their output will drop typically to
    about 2v or so. When they go faulty, they tend to give just the symptoms
    that you describe. There are usually type PQ3RD13 around too. These are
    +3.3v. I'm not certain if that model uses them, but have a look in your
    schematics, and if yes, have a careful check on their outputs with your DVM.


  5. Useless generic advice - and contradicts what the OP already said about this
    unit. The R-V905 has no thermal cutoff. It's detecting a power supply
    problem, though it could be falsely triggered.

    Mark Z.
  6. Loop the main (polarized!) power cord back into one of the switched outlets
    at the rear. Run a double - ended polarized cord from the other switched
    outlet to your variac or switched power strip. In this way you can bring up
    all the internal voltages without regard to protection status.

    A few Yamaha models had problems with the backup cap leaking near the
    microprocessor and causing problems like this - but I'm thinking your model
    is NOT one of these. Worth keeping in mind, though. If it comes to
    troubleshooting the protection function of the micro I can probably help.
    Post back here or you can e-mail me direct at:

    and revers the domain name to read

    Mark Z.
  7. N Cook

    N Cook Guest

    Important safety note:
    A mains cable with an unshrouded plug on either end is very dangerous
    practise, especially in the UK. If you must have such a cable lying around ,
    add some sort of springloaded shroud on one end. eg cable tie around the
    cable, to take one end of a spring and a small plastic bottle , cap end
    touching the other end of the spring. The bottle large enough to take the
    plug but deep enough when retracted to be reasonably enclosed.

    ps could anyone explain to me why my newsreader has failed to pick up the
    jackhammer posting, no cross-posting AFAICS, checking on Google grouips,
    which does have that posting. About once a week it occurs in a thread I'm
  8. Jamie

    Jamie Guest

    Check the caps in the power supply..
    You most likely have a bad one in the safety circuit and is
    shutting down due to a ripple in the voltage there.
    At least that is what I have found in a few amps I just recently
    serviced for a local business."
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