Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: lew247 on January 02, 2016,09:56:55
-
50LA620V the picture and sound it working perfectly
The problem is there is no backlight on it at all, the screen is totally dark, but if I get close enough to it I can see the picture perfectly, it just has no light at all
Do I need a new ccfl or could it be the inverter that the problem is?
Also
Any idea where I could find a service manual for this tv please?
-
OK, I'm stupid, LED tv's don't use ccfl's - they use strings of led's
I'm not used to working on LED tv's I'm more used to the old CRT types as I did my c&g224 many years ago
(I would imagine before led tv's were thought of)
Anyone got any suggestions or things it may be?
-
Hi Lew,
That could be a bit curly as LG service manuals are about as useful as a jockstrap in a blizzard. The LED driver board may be separate or it may be incorporated into the power supply, but find the lead that enters the back side of the panel from this board. It may be 2,3 or 4 pairs of wire or 1 or 2 flat flexie cables. The leads will be in pairs, 1 lead of each pair supplying volts to an LED strip or strips, the other an earth return that acts as an error sensor. The first will have high V, the second near 0V.
Measure the voltages wrt chassis earth at the connector on the board for a few seconds at the moment you switch the tv on. The hi-V ones should rise to a particular level, then drop off a bit and settle down. The voltages may also be marked at the plug on the board or marked something like L1+ and L1 for each pair and you're looking for a comparison of the hi-Vs. Not easy to describe without schematics or a board, but I'm home ATM.
If you find a hi-V that rises, but stays at that high level and doesn't drop back down, that lead will be feeding a faulty LED strip (probably an open LED) because there is no load on it. As the LED strips ignite they will gobble up some of the voltage. Some strips may be fed at a different voltage level to others. Just look for the drop-back in volts at the initial switch-on process to identify a strip that isn't drawing current ie it is inoperative due to a faulty LED or LEDs.
Bruce
-
Nice one Bruce,
Like Lew, transistors only appeared after my C&G final.
Triffic on valves, esp WW2 surplus.
Guess could make a return, as retro is a continual biz - Chris.
-
lew247 I personally think there is a manufacturer's fault with these LG Led backlights as there are a lot of these LG's I have seen with sever burns inside. Almost a fire hazard.
Strip your screen down and you would see a burn out area where the backlight has failed, usually 2 end strips. change that strip and your problem should be solved.
hope this helps
-
That's true, obagama, but I don't see LG putting out a product recall.
Bruce