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Power supply for back light of LCD monitor

Discussion in 'Electronic Repair' started by Bob Engelhardt, Sep 27, 2012.

  1. I have an HP Pavilion f1903 19" LCD monitor that has gone bad. The
    symptoms are a blank screen and a flashing power light. Google finds
    are pretty consistent that the problem is with the inverter board
    supplying the back lights. My DMM shows a few volts on the 4 outputs -
    not the "high" voltage warned of.

    Google found this page that describes the fix(es):
    http://h30434.www3.hp.com/t5/Deskto...Flashing-Power-Button-blank-screen/td-p/12212
    or
    http://tinyurl.com/95d3xw7

    It says first look for cold solder joints. I couldn't find any, but my
    eyes aren't what they used to be, even with a magnifier 8-(. Then,
    bulging caps (none of those), replace them anyhow. And, "might as well
    replace the power transistors while you're at it".

    If that's what it takes, it's not so bad (4 caps, 4 transistors, on a
    single-sided board). But I'd rather a more methodical approach that
    would actually identify the bad part(s), since I don't have the
    replacement caps & transistors.

    Your advice would be appreciated,
    Bob
     
  2. Jamie

    Jamie Guest

    bulging caps isn't the only item on the list when inspecting caps.

    You need to do a ESR test, if you have a meter that will do it, and
    do a capacitor value test. These are mainly the electros you find on the
    inverter board.

    Next problem. It most likely has a Xformer on the board or maybe even
    two of them. Check the windings, especially on the output, to make sure
    they are not opened. Also, look for HV caps on the output near the
    xformer if it has them.

    it also is possible you may have one or more fluorescent tubes out.
    Many inverters for the back light will not come on if it detects
    insufficient load, this would indicate a bad CLFL unit.

    THen there is always that possibility the main part of the system
    isn't starting.. .

    Jamie
     
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