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My Samsung PS50C91HX won't turn on. The power light lights up but that's it. The screen stays black. My small child kept pressing the on/off and then the set quit never to come on again. Someone said it may be the logic board. Any ideas what my son did to this television?

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  • robert_hayes Nov 20, 2009

    Thank you for the fast response. First off the power light is green and not flashing. It will go out when I press it and come on when I push it again. But nothing I connect to it brings the screen up. So I'm hoping this information may further help with this problem.
    Also it was unplugged for 3 weeks and still nothing.
    Thanks for the help!

  • robert_hayes Nov 20, 2009

    I will check the power supply and go from there! Thanks again for your direction.


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Rather than the logic board (that is also possible), your kid may have damaged the power supply, by turning on and off power button.

If after the fault the TV went in standby and does not wake up, then the TV has gone on protect mode after detecting a fault, probably caused by repeated switch on and off.

When this happens higher voltages are shut down to prevent further damage. The PSU will keep a low voltage +5V line to hold the TV in standby.

Try first leaving the TV power cord unplugged for some times, let say one hour or so.

Also ensure that the fault is not coming from a faulty receiver box sending bad signal, check if you get same problem with no receiver box or dvd connected.

If that does not work, and you keep having a flashing led on front of the TV, and tv turning off by itself after a while, that indicates a fault condition.

The flashing light indicates a diagnostic state called protection.
When the TV goes on protection there are only two possible reasons.

1The internal circuits are jammed because of electrostatic charges accumulating on capacitors, or because of a wrong voltage read by the main chip on your monitor controller board. this started the protection circuit.

2 The protection circuit detected a wrong voltage or a broken contact, identified an internal fault and kicked in , starting the flashing light.

If you are in situation one, then theTV will reset just unplugging power cord for one or two hours,sometimes even minutes.

If you are in situation 2 , then there is an internal fault.

Parts that may have blown after turning on and off are PSU (fault on higher voltages), logic board, sustain boards or buffer board.
The plasma TV must be tested to find out.

If the TV is less than one year old, then it is still under warranty, in that case contact the manufacturer ringing the number on the user manual

If you want to repair at your own expenses, just locate any good qualified repairer.


Posted on Nov 20, 2009

  • Ginko
    Ginko Nov 20, 2009


    Thanks for the clarification.

    The steady green light is not a great indication. Protect mode may show a different light and symptoms depending on the model.

    When the unit stays in standby and does not wake up then there is an internal fault.

    All I can tell you without testing is that the only part that makes repair not worth on this TV is the plasma display panel.

    If the problem happened clicking switch many times, then the panel is likely Ok.

    the part that gets more easily damaged by this operation is the Power Supply board, located behind the back panel.
    PSU capacitors are not allowed discharge because of the fast turning on and off, and they keep charging, until one of them will blow.
    Sometimes you can even notice that one of the big electrolytic capacitors in PSU is bulged or leaking.

    Parts for this set are difficult to find on third party distributors list. I checked the three biggest ones, no luck. In case I suggest calling Samsung to order the part or ask part price, or a quote on replacement. The PSU must be tested before replacement.



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