LG LCD TV model 42LH3000, picture colours incorrect

[Slartibartfarst]

LG LCD TV model 42LH3000, picture colours incorrect

I have had the above 42" LCD TV for just over 4 years and it has been working fine during that time until recently. While I was watching the TV, the picture suddenly started to display in the wrong colours (see attached photos).

I have tried the following (with no effect):
1) Used the option to reset the picture to default settings.
2) Used the option to reset the whole TV to factory settings including re-tuning all the channels.
3) Upgraded the firmware to the latest version.

The fault now appears immediately the set is turned on (from cold).

If you leave the set on long enough it looks like it might be going through a cycle as it does at some point briefly return to a normal picture before it continues on the cycle to incorrect colours again.

I would appreciate any help or advice that you can offer.

Kind Regards

[tom66]

Re: LG LCD TV model 42LH3000, picture colours incorrect

Possibly GAMMA chip fail. Can you post a pic of T-con board?

[Slartibartfarst]

Re: LG LCD TV model 42LH3000, picture colours incorrect

Thank you Tom.

I'm a complete novice with LCD TVs so I don't know what a T-con board is. Someone told me that they think there are 2 boards in my set - a main board and another one (the name of which I can't remember).

If there are indeed 2 boards in my set would the T-con be the smaller of the 2? What does the T-con board do? Is that where the Gamma chip is? I've never taken one of these sets apart before, so I'm a bit reluctant in case I can't get it back together again.

If the gamma chip is dead will I need to replace the board? If so are there generally any very awkward steps involved in replacing a board?

Thank you

Jeff

[tom66]

Re: LG LCD TV model 42LH3000, picture colours incorrect

There is a main board, which has HDMI and the antenna connector on it.
There is also a power board, which takes AC power in.
There are boards for the buttons and lights - not particularly important now.
Of most interest will be the board at the top of the panel, the t-con board.

[Slartibartfarst]

Re: LG LCD TV model 42LH3000, picture colours incorrect

Picture of the t-con board attached Tom.

[tom66]

Re: LG LCD TV model 42LH3000, picture colours incorrect

OK, see this picture. In the red area, and possibly a little outside it, there are points marked VG1 through VG22 (typically.) Please measure the voltage on each and report the reading for each. (Red circle around one point as an example.)

To measure: multimeter on auto range volts DC or 20V DC (whichever it has), black probe on chassis, red probe on test point, note reading down. Rinse and repeat.

[Slartibartfarst]

Re: LG LCD TV model 42LH3000, picture colours incorrect

I'm struggling to see such tiny connections Tom. I think I'm inclined to take the risk and spend £37 on a replacement T-con board. But I appreciate your efforts helping me to pin it down with more certainty.

Thank you

Jeff

[newtothis]

Re: LG LCD TV model 42LH3000, picture colours incorrect

I am picking up with of these sets tomorrow with the same fault, Will try helping you out once i get it

I suspect T-con... Seems a weak point on these sets

£37! I got one off the bay for £18 inc P&P

Also if you look at the pic tom edited.. the little circle inside the bigger circle is a test point... they are the little round copper pads with VG10 etc next to them... check them all and report findings.

These T-cons use the AS15 gamma chip and are prone to failing with the distorted colours, You can actually replace just the Gamma IC but need a few tools and be confident in fine pitch soldering to do so.

[newtothis]

Re: LG LCD TV model 42LH3000, picture colours incorrect

To make it easier.... Click on the picture below..

I have highlighted a few of the VG test points... so you know what you are looking for.

[newtothis]

Re: LG LCD TV model 42LH3000, picture colours incorrect

OK I have the TV... Same fault by seems of it.. AS15

[tom66]

Re: LG LCD TV model 42LH3000, picture colours incorrect

There are some others on the other side of the board, too. Need to test VG1 thru VG22.

[irep]

Re: LG LCD TV model 42LH3000, picture colours incorrect

I have in hands a 42LH3000 color problem, just checking voltage on Tcon, if it has voltage on VG test points and color not correct it assumes that a board problem?

Not power assy.
I´de like some help in this point.

[tom66]

Re: LG LCD TV model 42LH3000, picture colours incorrect

No, the VG will have a voltage regardless of working or not, but the specific curve of voltages they plot from 1-22 or 22-1 needs to be correct. If you post your values we can give some guidance as to whether they are correct or not.

[irep]

Re: LG LCD TV model 42LH3000, picture colours incorrect

some mesure:

VG1 - 15,22
VG2 - 15,10
VG8 - 9,99
VG10 -8,03
VG11 - 7,07
VG12 - 7,30
VG13 - 7,80
VG15 - 5,14
VG17 - 11,87
VG19 - 2,89
VG21 - 0,60
VG22 - 0,29

[tom66]

Re: LG LCD TV model 42LH3000, picture colours incorrect

The voltages are bad, so you will need to replace AS15 IC.

[irep]

Re: LG LCD TV model 42LH3000, picture colours incorrect

Ok Tom66, or get a new board.

Thanks you for the rapid answer.

Cheers

[tom66]

Re: LG LCD TV model 42LH3000, picture colours incorrect

"New board" an expensive option as about half of them are bad (they are used parts.) Only if factory direct or LG direct.

[irep]

Re: LG LCD TV model 42LH3000, picture colours incorrect

i will search on manual the reference number of chip and try to get it

[irep]

Re: LG LCD TV model 42LH3000, picture colours incorrect

Tom66

You are wright, i can get it in my country for 5 eur.

Very nice price.

Nice tip