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Sharp TV dead

Discussion in 'Electronic Repair' started by Golf, Jul 3, 2006.

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  1. Golf

    Golf Guest

    I have a model #27F-S120 TV that is dead. Raw B+ good to power
    transformer. No low voltage on primary of power up relay. I have
    studied the board for over an hour and simply can't see where the stand
    by voltage is supplied, to further troubleshoot. Hoping someone may
    have a schematic, or knowledge of this particular model/problem.
    Thankyou group as always, still a beginner here.
     
  2. Tech Data

    Tech Data Guest

    On the other side of the 'power transformer' , actually the standby
    transformer, you'll see 4 diodes. That's the bridge for the standby 24
    volts. If that voltage isn't there, then you have an open winding in
    that transformer. Really common fail. If it's still available, runs
    around 25bucks. If not, there's other options.

    www.techdata-kicksass.net
     
  3. Golf

    Golf Guest

    Thanks asskicker, I have 120V on the primary, zero on the secondary.
    The way it looks though, the power on relay must energize to supply
    current to the transformer primary, and induce a voltage in the
    secondary. How is this standby transformer made/wired? Their is an IC
    (full bridge rectifier), on the secondary that is connected to the 24V
    of the relay. I trust your info, just don't fully understand. Thanks
    again techdata.
     
  4. Tech Data

    Tech Data Guest

    Ok, to cut it short, the ac line in goes straight to the primary of
    that transformer. That alone energizes the windings to induce the 24
    volt standby source which also goes to the relay, as well as the 12,9
    and 5 volt lines. When the relay latches, THEN ac is routed to the
    primary of the swithcing power supply that provides the B+ for the
    horizontal circuit. Without the smaller standby transformer working,
    NOTHING else is going to work. To prove or disprove, use an ohm meter
    and measure resistance on the two secondary pins of that transformer. I
    got a buck says they're open. Should read shorted or near shorted.
    There may or may not be a thermal fuse inside the transformer but, the
    way that's designed, you'll destroy it before you get to it. Best to
    replace.

    www.techdata-kicksass.net
     
  5. Golf

    Golf Guest

     
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