Model LD-4258
Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/
Some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement.
SOURCE: screen goes black but still have sound
MINE TOO AND SANYO TOOK THIS TV OFF ITS SUPPORT WE SHOULD ALL SUE THIS COMPANY [email protected]
SOURCE: screen goes black,with sound
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.
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
SOURCE: HELP! KDFE55A20 watching TV and screen goes black and loses sound
Yes, its most probably lamp issue.
Please but original Sony lamp from Sony store and replace it in TV.
SOURCE: power led blinks but no picture or sound
Had the same problem myself. Took some doing but I managed to find a service bulletin that I downloaded. The problem is with the siene module and all you need to do is unplug connector JP63A from the main board and your TV will work again.
Take the back off the TV (there are a lot of screws) and look on the left hand side of the main circuit board that is mounted in the center of the TV. You will see a small white connector that is labelled JP63A, simply unplug it. Plug the TV back in and let it reboot. That's it, should be able to watch immediately.
SOURCE: video flickers on and off
Bad capacitors in the unit that are in the signal board.
Testimonial: "Guess this means if warranty is active, send it to get fixed, otherwise buy new TV. OK, thanks!"
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