Question about Sharp 20F640 20" TV

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Beeping noise and no power

I have a Sharp TV and I turned it off and noticed a beeping noise somthing simular to a cricket. When I went to turn it back on it didn't work. The power light didn't come on or anything.

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The "cricket" sound you heard can mean any number of things:

1. A component in the power supply that sets the frequency failed, causing a high frequency (hence over-voltage) in the SMPS, which then also failed. The initial failure may have occurred in a small high-voltage capacitor in the power supply (around 160V or so rated)

2. A failed horizontal drive or vertical stage, which drew so much current that the switching semiconductor in the SMPS failed.

Note that such failures often occur like dominoes (one, then two, then three, and so on). Sometimes the fuse itself will not even blow out. The best thing to do is to first remove the line-output transistor and then replace the switching semiconductor(s), nearby zeners, capacitors, and fuse if blown. Then turn the unit on and check for about 105V on the collector terminal of the line transistor. If that's fine then turn unit off, replace the line transistor.

Of course the above procedure is only a guide; the precise steps taken will depend on your exact make and model. Also, if the above sounds mind boggling then rather take it down to your nearest repair shop. Good luck.

Posted on Jan 18, 2008


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