LG 42LH50 Turns on has backlight no picture.

[Shinju]

Hey all!

I just picked up this LG Broadband LCD Panel, When I plug it in the red standby light comes on, hit the power button the red LED blinks a few times then changes to blue and the backlights come on and nothing else.

I tried cycling through the inputs to see if I got sound but I couldn't seem to get any audio.

Any suggestions on what to test for when I crack it open? T-con/mainboard?

Thanks!

(sorry no gut shots yet, will dive into it hopefully on Friday!)

[budm]

Re: LG 42LH50 Turns on has backlight no picture.

T-CON fuses and voltage on both ends of the fuse.

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

T-CON fuses and voltage on both ends of the fuse.

Will do! I did do a search and it seems this panel has not been here yet so I will do my best to document what I find for future references.

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

So I got a minute to tear I to this. I cleaned and reseated every cable I could, no change, I checked the voltage on both sides of the fuse on the t-con if I set the DMM right I saw 12.15v on each side. There is a small blue LED that illuminates on the t-con for about 20-30 seconds after the unit is powered up is slowly dims after the 30 seconds. Also there is a red constant led on the mainboard.

Here are some photos.

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

/bump

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

I think it just might be the mainboard, I cannot get audio VIA HDMI I will try Analog inputs and see.

[budm]

Re: LG 42LH50 Turns on has backlight no picture.

How are the voltages on some of those test points on the T-CON board? I.E. VIN, VCC, VGH_M, VGL, VGH, and U11?
http://www.shopjimmy.com/media/catal...-4700f-top.jpg

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

Assuming these are correct

VIN 12.12
VCC 3.32 (not sure if this was the right point as my t-con is 120hz looks different in areas)
VGH_M 25.2
VGL 4.83
ULL 1.19 (not sure as my U11 was located different if it was the chip or the pad next to the top of it)

Also the VCC painted text looks like it was half gone, photos inc.

[budm]

Re: LG 42LH50 Turns on has backlight no picture.

Well it looks like the sub voltages are present. BTW, did you try having just one ribbon cable between the T-CON and the LCD panel connected one at time to see what you get?

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

I will try that, since there is 4 cables total I am assuming you mean pull one from the top and turn it on?

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

The top 2, what ever side was unplugged was White other side was black. Unplugging either of the bottom 2 cables did nothing.

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

Just tried 2 tested working t-con boards and still the same.

[budm]

Re: LG 42LH50 Turns on has backlight no picture.

You will have to try using the scope to see if you do have any LVDS from the main board feeding the T-CON next.

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

O-scope? I don't have access to one anymore.

Anything else I can try?

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

Got a working mainboard all numbers match and still he same issue.

Any other suggestions?

[Glitcher]

Re: LG 42LH50 Turns on has backlight no picture.

I would guess towards the tcon board, otherwise panel.

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

Hmm possible but I am going to try and stay positive that is something else.

When I disconnect either side of the upper t-con the half the screen goes white on the side that's unplugged as you can see here.

The red LED being illuminated on the mainboard up on power up seems to me something is halting the mainboard from going further.

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

Apperently this is an EEFL backlit panal, the blue LED on the t-con excites the EEFL lamps into firing so that's the purpose of that led.

The red LED on the mainboard LD2400 the manual states use it as a visual guide but doesn't state anything about illumination or if it changes color if the 3 things is monitors is working

Here is the manual, maybe someone here can decipher what it means of you want of have time. Ugh lol if I wasnt 80.00 deep in it I probably would just scrap it.

http://www.scribd.com/mobile/doc/214500864#

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

Also, would a bad panel cause the audio to not function too?

[Shinju]

Re: LG 42LH50 Turns on has backlight no picture.

/bump

Open to suggestions!

Also if anyone else reads this here or via google and you have a working unit please chime in on the LED LD2400 light you can see it from the back of the panel just above the input section on the upper right side plain as day if its illuminated!