Question about Philips 42FD9954 42 in. Plasma HDTV

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Screen goes black,with sound

Screen goes black,some times only half screen.sound is on,it happens when its on for about 1 hr.please help

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  • romypautsch Oct 20, 2008

    I have no screen display. It was working til last night. There is a red sensor light flashing and everytime I press the power button nothing happens...including the sound of the power when turned on. Hope this makes sense.

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No picture sound ok
Note 1 a Raster is the name for a screen made of lines of brightness
Note 2, A Blank raster has no snow or picture, its just a lit up screen

Sound ok but no raster.
First increase tube's first anode voltage (knob on the loptx) to see if the screen is just too dark.
if after you have turned up the bottom knob on the loptx, there is still no brightness,check, for crt heaters, and EHT 25kv and focus voltage (2kv) and A1's/Screen/G2 voltage is 300-600v.
and check for field timebase (height), the next thing to check is the sandcastle pulse.
If it's present, colour decoder chip is probably faulty or lacks supply from the LT regulators.

NO LINE DRIVE If it's absent,check the line driver, locate the loptr(big and usually has heat sink).
follow the print from the base back to the driver stage , where you will usually find a tiny transformer with 4/5 pins
resolder it, even if it looks good,then with power on, check for voltage on all its pins, 2 should have LT(12v to 32v) or HT (90v to 150v), if not there follow the print back and look for either a transistor(linedrivetr), or the feed voltage line (maybe regulated),
If the voltage is ok on two of the driver transformer(drvtx) legs, the look from the base of the driver transistor to locate the timebase chip
and check round its pins for a 12v supply line, if there ,replace the timebase generator chip

Method of testing line drive, remove line output transistor, and connect a normal red led, across the B/E (longest leg to base), and when you power up the led should lite up.


Trace the pcb back from the BASE leg to find the line driver stage,
Its usually a very small transformer (4/5 legs) and a transistor connected to it,
The driver transformer legs(pins) will be two with voltage and two without
The two with power will either be about HT level (110v=145v) or about LT level(25v)
If not then trace back and look for a biggish 3w resistor.
screen goes black,with sound - linedrv.jpg
If the voltages are correct the look for line pulses from the Timebase oscillator chip to the base (some overvolts protection circuits remove pulses if ht is too high).
If the voltage is low and the feed resistor is getting hot then check the base of the driver transistor if its HI over 0.5V then its being turned on by the timebase oscillator chip (protection ?)
If the voltage is zero check the feed resistor
If all seems normal check that 12v is getting to the timebase oscillator chip (IC) (12v regulator?)
Method of testing line drive, remove line output transistor, and connect a normal red led, across the B/E (longest leg to base), and when you power up the led should lite up.

Hope it may help you;
Regards,
VOTIT

Posted on Oct 10, 2008

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