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help with classic NAD MR-20

Discussion in 'Electronic Repair' started by William Sommerwerck, Sep 1, 2007.

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  1. I'm new to this group. I'm a BS EE who's serviced electronic equipment most
    of his life, so don't hesitate to get as technical as you like.

    When I reviewed the NAD MR-20 for Stereophile 20+ years ago, I was so
    impressed I bought one. It's given me yeoman service; I suspect it has 20K
    hours on it. Until now, the only problem was some bad electrolytics on the
    video driver board.

    The current problem is intermittent loss of brightness accompanied by loss
    of focus. Adjusting the Screen and Focus controls improved things, and
    removing the back greatly reduced the frequency of the problem (presumably
    because the set runs cooler).

    This might be the CRT, but I suspect it's the HV rectifier. (Tapping the
    neck of the CRT has no effect, but that's not a definitive test.)

    The problem is that the HV rectifier appears to be potted within the flyback
    transformer assembly. The transformer is no longer available (nor is the
    CRT). Before I yank the transformer (it's not easily removed), I need to
    know whether the HV rectifier is accessible. And, of course, I'd appreciate
    _any_ thoughts on servicing this set.

    Thanks in advance.
     
  2. Chuck

    Chuck Guest


    The HV rectifier is in the flyback assembly. As a side note, I
    purchased the last flyback NAD had in stock about 7 years ago. It was
    the second most likely part to fail. The first being the electrolytic
    capacitor on the crt board. This set was actually made by Sampo but I
    don't believe any set made under their name used this flyback. Chuck
     
  3. Thanks for the info. I won't be rushing to remove the flyback.

    I assume you mean C13. Electrolytics are cheap, so I ought to replace a
    bunch.

    NAD's idea was, instead of designing a new color TV from scratch, they'd
    pick a "good" existing model and improve it. The Sampo was their choice, but
    it required more upgrading than they expected.
     
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