Question about Samsung LN-T5781F TV

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SOUND OK BUT NO PICTURE.

I HAVE A SAMSUNG TANTUS 43" PROJECTION T.V silver colour 3 guns ,chassis no PCL545R, mechanic suggest s to change PCB part THYRISTOR no 2SD 921 .
EXPERT OPINION REQUIRED.




THANX.

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The 2sd921 is not a thyristor, but a High Speed Switching Transistor. It's used in the HV circuit of older televisions. If is is for the HV, make sure that he re-solders the horz driver transformer while he's at it, also check the hv safety caps. Just a word of caution, the CRT's in that model have a history of arcing, that could be why your 2sd took a dive. If that's the case don't have it repaired, besides I doubt if you'll be able to get them.

Posted on Feb 28, 2009

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THAT MAKES SENSE, CHECK FOR HIGH VOLTAGE- YOU CAN SIMPLY HOLD A NY SMALL NEON BULB[LIKE THOSE USED IN PILOT AMPS] NEAR THE ANODE LEAD OR FLYBACK TRANSFORMER IF IT'S ACCESSABLE, AND IT SHOULD GLOW. THE NEXT STEP IS TO CHECK THE FILAMENT CIRCUIT FOR THE PROJECTION TUBES- OFTEN IN MODERN SETS, THE FILAMENT [HEATER]VOLTAGE IS OBTAINED WITH A COUPLE WINDINGS AROUND THHE FLYBACK. IF YOU HAVE HIGH VOLTAGEE, AND NO FILAMENT, A 'HACK' THAT WORKS IS TO USE A SMALL POWER TRANSFORMER [MOST FILAMENTS [HEATERS] ARE 6.3 VOLTS, BUT DOUBLE CHECK THAT- IF YOU HAPPEN TO HAVE ONE OF THE LESS COMMON LOW VOLTAGE HEATERS, AND YOU OVER-VOLTAGE IT, YOU'VE JUST DESTROYED A VERY EXPENSIVE TUBE.THE 2SD921 IS IN AL LIKEYHOOD THE HORIZONTAL OUTPUT, WHICH DRIVES THE HIGH VOLTAGE CIRCUIT. IF YOU HAVE A SCOPE, CHECK FOR APPROX 15KHZ SIGNAL AT THE EMMITTER OR BASE- BUT BE CAREFUL ABOUT THE GROUND LEAD- USE A 3 PRONG ADAPTER, AND DEFEAT THE EARTH GROUND OF THE SCOPE, OR YOU COULD DAMAGE THE TV'S POWER SUPPLY

Posted on Feb 28, 2009

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