42LG20-UM LCD TV washed out picture

[chris1sr]

Hi everyone I have a 42LG20-UM LCD TV and I need help Diagnosing picture problem. When the TV is first turned on everything works fine but after a few minutes the pictures slowly losses its contrast and becomes washed out. Also the power light flashes green 6 times at startup. I have started testing the power supply and everything seems fine.i have attached pictures of the components and believe the problem is either the power supply, main board or the T-Con what do you think?
Thanks
Chris

[budm]

Re: 42LG20-UM LCD TV washed out picture

Looks like bad Gamma Voltage, remove the Silicone thermal pad from the IC on the top right of the T-CON board to see if it is AS15 or AS19.
You can also take the DCV readings of the Gamma Voltages at the test points on the board.

[CapLeaker]

Re: 42LG20-UM LCD TV washed out picture

Looks to me the same what budm said.

[chris1sr]

Re: 42LG20-UM LCD TV washed out picture

Thank you budm and CapLeaker for your quick response. Yes it is an AS15, I had to put on two pairs of glasses to read it. how can I take the DCV readings of the Gamma Voltages at the test points on the board? What should they read and does this mean the T-Con is bad?

[chris1sr]

Re: 42LG20-UM LCD TV washed out picture

T-Con picture attached

[budm]

Re: 42LG20-UM LCD TV washed out picture

OK, AS15 Gamma ref IC.
Does it get to be to hot to touch when the screen washed out?

[chris1sr]

Re: 42LG20-UM LCD TV washed out picture

No, I waited five minutes the screen washed out in about two the AS15 just felt slightly warm,
Thanks
Chris

[CapLeaker]

Re: 42LG20-UM LCD TV washed out picture

You can replace that AS-15 IC if you comfortable doing this, or replace the T-con.

[mmartell]

Re: 42LG20-UM LCD TV washed out picture

Record the VGMAxx dc voltages and post here like..

VGMA22 12.2v
VGMA21 11.9v
.
.
.
VGMA1 3.2v

[chris1sr]

Re: 42LG20-UM LCD TV washed out picture

Thanks Mmartell

Just got back to this, hear are the voltages they seemed to go up a little as the TV warmed up:

VGMA1 14.40
VGMA2 14.35
VGMA3 14.37
VGMA4 14.05
VGMA5 13.83
VGMA6 13.77
VGMA7 13.75
VGMA8 13.72
VGMA9 13.58
VGMA10 13.34
VGMA11 13.14
VGMA12 6.36
VGMA13 6.23
VGMA14 6.05
VGMA15 4.51
VGMA16 4.25
VGMA17 3.71
VGMA18 2.90
VGMA19 2.23
VGMA20 .52
VGMA21 .42
VGMA22 .29

[ReeceyBurger123]

Re: 42LG20-UM LCD TV washed out picture

Yep your As15 has failed. Try changing the Ic.

[chris1sr]

Re: 42LG20-UM LCD TV washed out picture

Is there a good site to buy a T-Con Board?

[ReeceyBurger123]

Re: 42LG20-UM LCD TV washed out picture

Ebay I mainly use if not check google etc.

[Markus1]

Re: 42LG20-UM LCD TV washed out picture

Did you replace T-Con board?
Did it solve the problem?

[budm]

Re: 42LG20-UM LCD TV washed out picture

Did you replace T-Con board?
Did it solve the problem?

Same problem as OP?
Did you test the GAMMA Voltages?

[Markus1]

Re: 42LG20-UM LCD TV washed out picture

Yep your As15 has failed. Try changing the Ic.

ReeceyBurger123 - Could you please explain what actually indicates in the VGMA readings above that the AS15 has failed?
The voltages show continuous decrease in values, as it should be, I believe.
Although there is a bigger jump between VGMA11 and 12. Would this be enough to say that the AS15 is bad?

I am not questioning your assessment here, just trying to learn a bit more.

[diif]

Re: 42LG20-UM LCD TV washed out picture

ReeceyBurger123 - Could you please explain what actually indicates in the VGMA readings above that the AS15 has failed?
The voltages show continuous decrease in values, as it should be, I believe.
Although there is a bigger jump between VGMA11 and 12. Would this be enough to say that the AS15 is bad?

I am not questioning your assessment here, just trying to learn a bit more.

The voltages have to decrease evenly. There is a spreadsheet and more info in this thread.
https://www.badcaps.net/forum/showthread.php?t=35301

[mmartell]

Re: 42LG20-UM LCD TV washed out picture

The voltages show continuous decrease in values, as it should be, I believe.
Although there is a bigger jump between VGMA11 and 12.

Bigger jump than the OP's ? Then yes, yours is bad as well.

[Markus1]

Re: 42LG20-UM LCD TV washed out picture

Same problem as OP?
Did you test the GAMMA Voltages?

Different TV model, similar problem with a pale, washed out picture.
Gamma voltages as follows;
1 15.31V
2 15.26V
6 14.10V
7 13.92V
8 13.84V
10 13.40V
11 13.32V
12 6.63V
13 6.37V
15 4.69V
16 4.39V
17 3.86V
21 0.50V
22 0.36V

There is a wider jump between VGAM 11 and 12. In fact Very similar to that shown by OP in post #10.
Not sure if that jump is too big though.

The chip AS15F (with heat transferring pad removed) is warm and certainly not too hot to touch.
Supply voltage (on F1 SMD fuse) is 11.6 V.

So, is it the chip or anything else on the T-Con?

[CapLeaker]

Re: 42LG20-UM LCD TV washed out picture

The as-15.