Logik l423ed11 vertical lines

[efwiofoi]

i have a logik l423ed11 42inch lcd, the picture shows a vertical line that moves from left to right, i think it's the 'no signal' logo which is moving about. if i press menu a wider pattern comes up in the middle.



any ideas what this would be, panel / main board / tcon?

thanks

[tom66]

Re: Logik l423ed11 vertical lines

It's a fairly new TV so I'd be going "PANEL!!"
There is a chance, if the t-con is separate, that a loss of VGH or VGL voltage could also cause this.

BTW, you never PM'd me back about the Vestel board, are you still interested in it?

[efwiofoi]

Re: Logik l423ed11 vertical lines

hi tom i was thinking the same

it does have a tcon though so maybe there is hope?

it has an LG panel LC420EUN, with an upside down tcon













re the vestel board yes, i will pm you about it.

[tom66]

Re: Logik l423ed11 vertical lines

Need a shot of this board.
https://www.badcaps.net/forum/attach...3&d=1390070388

where the labels can be seen for test voltages. Like VON, VOFF, or alternatively VGH and VGL.

[efwiofoi]

Re: Logik l423ed11 vertical lines

here is a close up of the tcon




there is 11.85v on the main fuse.
what else can i check?

the main board has a jumper that sets either 5 or 12v for the tcon



i can get the tcon on ebay, £20

[efwiofoi]

Re: Logik l423ed11 vertical lines

the pads on the right half mostly measure -.97v
the left most one (vcomrfb?) is 5.61v and vcom is 5.61
z out is 5.8

[efwiofoi]

Re: Logik l423ed11 vertical lines

[tom66]

Re: Logik l423ed11 vertical lines

See image. Test each ringed point, board plugged in and set powered up, DC volts, red probe on point, black probe on chassis. Report adjacent label to each point - VGL, VGH, AVDD, AVCC, Vcore, VCOM_FB.

[efwiofoi]

Re: Logik l423ed11 vertical lines

ok i get:

VGL -0.97v
VGH -0.73v
AVDD 11.56v
AVCC 3.29v
Vcore 1.97v
VCOM_FB 5.14v

[tom66]

Re: Logik l423ed11 vertical lines

VGL and VGH are your problem. I bet, since voltages are so close, there is a short between them in the panel. Try unplugging one ribbon at a time and see what happens, sadly this will probably NOT be repairable.

[efwiofoi]

Re: Logik l423ed11 vertical lines

with the ribbon near them out they are the same (vgl -0.97 vgh -0.73). with the other ribbon out only, vgl is -1.56 and vgh is -0.73

with both ribbons disconnected: vgl is -1.56 and vgh is -0.73

[tom66]

Re: Logik l423ed11 vertical lines

Sounds like a short, which has since damaged them, you could try replacing the components around there (likely a transistor or resistor) or the t-con but I suspect there's a fair chance they'll fail shortly afterwards due to panel fault.

[efwiofoi]

Re: Logik l423ed11 vertical lines

ok
thanks for the help. what voltage should vgl and vgh be?

[tom66]

Re: Logik l423ed11 vertical lines

VGL around -5V to -10V for all panels.
VGH around +20V to +28V for early panels, +17V to +30V for newer panels like this.

The VGL deselects a line on the screen, so it doesn't take data, VGH selects it, the Gate in Panel driver (see DS: ) swings between VGL and VGH for each line in the screen.

So when a line is at VGL, it is "muted" and it is not looking for data, when it is at VGH it is listening for data, in between the two it could do either, I think that's why all lines show the same.

[efwiofoi]

Re: Logik l423ed11 vertical lines

i bought a new tcon, connected it up without the screen ribbons and measured +28v on vgh and -5 on vgl.
as soon as i powered it up with the ribbons connected there was a burning smell from the tcon. the voltages are back to around -0.7 again.

i took the panel out and removed the bezel to see the boards that are bonded to the screen. nothing much to see except one is sticky. looking at the edge of the panel something has been spilled on the screen and run down onto the left board (panel is mounted upside down). it looks like it was coke, its brown and sticky. theres not much on these boards only 2 pin components. i think there's a chance if i clean this off and buy another tcon it might work?alcohol spray and a tooth brush?

[truep]

Re: Logik l423ed11 vertical lines

Very little chance, I' would give it a try though. I've had four with liquid damage and none worked after cleaning. If it got on the cables to the panel, forget trying to fix it.

[efwiofoi]

Re: Logik l423ed11 vertical lines

it got on one of the ribbons, after cleaning there is a little black dot between two gold pins where the ribbon bonds to the pcb. in two minds whether to try another tcon, i think i might leave it.

bit of a step backwards putting the ribbons at the lower edge

[tom66]

Re: Logik l423ed11 vertical lines

They put 'em on the bottom because they were getting too hot at the top, but the massive disadvantage means ANY liquid spill has a good chance of wrecking the panel. At least tab bonds were fixable... it feels like it's a deliberate failure mode... a little sealant around the bottom of the panel and it'd all be OK, but no...

I had a 37" LG LED with water damage, half screen missing, couldn't fix it.

[efwiofoi]

Re: Logik l423ed11 vertical lines

another one for the scrap heap
it kind of fits better now they started putting the tcon underneath, leaving it thinner at the top, but many more unrepairable tvs, as its common to get something spilled on the screen.

they are never going to bother sealing it, it might cause problems as well due to a small amount of movement needed for thermal expansion.
bad news for lcd's

[tom66]

Re: Logik l423ed11 vertical lines

LCDs are less reliable than plasmas. Let's hope OLED are better, but somehow, I don't see that they will be.