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Denon AV reciever shut down

Discussion in 'Electronic Repair' started by Bob Urz, Apr 26, 2007.

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  1. Bob Urz

    Bob Urz Guest

    I got an Denon AV receiver in that immediately goes into shutdown. Plug
    it in, no display. Hit the momentary power up switch, relay clicks by
    small power transformer, display goes through two different displays,
    relay clicks again and display goes mute. It says nothing on the display
    about protection or such. Non of the outputs seem to be shorted.
    Ot seems like a classic case of outputs shorted and the unit shutting
    down, but the outputs are not shorted and the display does not say
    protect before it goes blank. I resoldered up the main board and no
    change. ESR'ed the caps and nothing jumped out bad. DOn't have the print
    yet but that next if the customer wants to pony up more bucks.
    Any ideas on the shutdown? I'll post the model number latter.

    Bob
     
  2. N Cook

    N Cook Guest

    =----

    Perhaps something like a zener has drifted so its falsely registering an
    imbalance of B+/B- or something. If you are loathe to temporarily disable
    the protection cct,for diagnosis, try adding a power diode or into one DC
    rail and then the other to see if there is a change.
     
  3. **In cases like this (all too frequent, with modern equipment) I bypass the
    power relay contacts and ramp the unit up with a VariacT. Watch for smoke,
    of course.
     
  4. Arfa Daily

    Arfa Daily Guest

    Ditto

    Arfa
     
  5. Had a Denon recently with a similar problem - it was a bad 7815 regulator.
    It was necessary to disable the protection circuit by lifting a diode in
    order to troubleshoot. In my case bypassing the relay didn't work - it still
    triggered the protect without revealing any cause, since the problem
    disappeared as soon as the protect triggered. When the protect was disabled
    a wall-to-wall 60 hz sine wave appeared at the output of the amp. Good thing
    there was no load at the time...

    MarkZ .
     
  6. Bob Urz

    Bob Urz Guest

    Thanks Mark, you got me on the right track. I had the high voltage
    rails. But the center voltage on all the outputs was 1/2 of the B+ rail.
    I had hot wired the turn on relay. There was a 5 volt 3 legged regulator
    and it was fine. BUT, right next to it was another low rail with 4
    discrete diodes with a 1/2 watt resistor in series with the power
    transformer. This resistor was open. None of the diodes were shorted.
    replaced the resistor, checked all else, and it fired up.

    Bob
     
  7. Cool!

    mz
     
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