Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: sawasawa2 on December 29, 2011,06:36:58
-
:sign0144: This LCD set is a new venture after many years of CRT and video repair. This set has what seems like a back light problem in that the top 1/3 of the display is normal brightness but the lower 2/3 is very dark. Using a colour bar input the colours on the lower 2/3 are much darker with yellow being almost brown. This morning the power supply quit but fortunately a spare unit had been supplied, but no change to the original fault when fitted. Strangely, after I received the set and confirmed the fault, it disappeared and the set worked OK for about 2 weeks, then the fault returned. Have tried various adjustments and factory resets but got nowhere. Any help would be appreciated. Derek
-
what is the screen type fitted, if the lamps are in parallel as some are now you may have a lamp or two out, on sets fitted with multiple outputs error detection is carried out but the parallel ones have been known to continue
-
Thanks for reply TV Tony. Slight delay due to festivities! Screen type? other than being LCD, can't find any other info. No part numbers visible. What appears to be the wiring for the backlighting comes off PL802 1-5 which according to the schematic are 24V supplies and this is the only loom that goes through the back shield. Are backlight tubes normally 24V? And are they installed horizontally across the back of the screen or is edgelighting normal? Horizontal seems to be indicated by the nature of the faulty display, being split horizontally.
I should have mentioned earlier that the fault is apparent with no signal input, and so far, not tapworthy.
Are replacement tubes available? Looks like a dockyard job to get at them! Cheers Derek
-
The tubes operate from high voltage.
If all you can see is a bundle of 24V wires dissapearing through the chassis, then your set has the inverter board burried behind the first chassis layer, which can be a PITA to get at. Lots of dismantling, then very often hard to jig them so you can power up with it all exposed.
-
Hi Derek,
This seems to be a modern set (have no details apart from PS cap probs) most older sets had inverter panels with individual connections to tubes, some few others had just two backlight connections where tubes were presumably connected in parellel (not yet had had a screen apart to check)
Thought is - how many feeds to the backlights - Chris
PS - Thanks Pro-Dave, and Prosperous N/Y our chum, your input beat mine to the post
-
Thanks for the info guys. No. of wires going through back plate, all from PL802, 5 x24V,3 ground, 1 yellow,1 blue from pins 11 & 12. Looks like it'll be a dockyard job - or off to the scrappy. Cheers Derek
-
I should have mentioned that PL802 pins 11 & 12 are marked A DIM and BL ON OFF, whatever that might mean. This line is connected to a pnp transistor emitter, rigged as a switch but can't find the other end of either A DIM or BL ON OFF. Need the rest of the schematic. Will do some voltage checks asap. Cheers Derek
-
One tip for later sets which have various fmw problems go to customer DVB menu and choose/perform "First Time Installation". This rewrites a basic version of the fmw and can cure a multitude of problems
may help :33: