Sanyo DP26670 cej508a PS problem

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  • craigc15
    Senior Member
    • Jun 2012
    • 53
    • USA
    #1

    Sanyo DP26670 cej508a PS problem

    I'm working on this Sanyo 26" (It's in like new condition, otherwise I wouldn't bother) and the backlight power supply is only putting out around 17v.
    I've checked and replaced the 2 caps in the circuit, the KIA431 shunt regulator and the MOSFET with no success. I can't locate a schematic but from what I can see on the board, it's a circuit I haven't seen before.
    The backlight supply has a MOSFET on the secondary side of the xfmr (labeled "MOSFET" in the attached pic). The drain of the MOSFET has 27 V (unloaded) and the source has about 19v. It's an N-channel FET (2SK3703) whose gate seems to be controlled by the shunt regulator. When I take the MOSFET out and short the D-S, the backlight works fine, but I can't figure out why the MOSFET doesn't seem to be turning on completely when it's in the circuit, which I thought would blow the MOSFET. I checked the gate, drain and source with my frequency meter and there doesn't seem to be any PWM happening.
    I guess I could just take the MOSFET out and leave it shorted, but I tend to like to leave circuits as designed.

    Any help would be greatly appreciated!

    Craig
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