M421VT LED Screen Color Distortion

[dfang]

I have a VIZIO M421VT LED TV and it's got what I will call a color display distortion problem. I'm a novice at TV repair and would appreciate some advice with which direction to go with this one...Some times when it's turned on,,the picture is good,,then after about 20 min or so,,it will go to bad. I tried heating up main board,T-Con and PS with no noticeable effects.. Sound is good and all channels work..Any help appreciated..

[dfang]

Re: M421VT LED Screen Color Distortion

To scrap or not to scrap,,,that is the question..

Could someone please give a educated guess as to what could be the problem ?

Thanks..

[tom66]

Re: M421VT LED Screen Color Distortion

I have seen this fault before caused by a loose ribbon cable (LVDS cable) between the main & T-con boards.

[dfang]

Re: M421VT LED Screen Color Distortion

Thank you Tom for the suggestion..
I did notice a burn mark on the right side LVDS cable at the T-con..
Cleaned the T-Con contacts and tried another cable,,no luck..Maybe the T-con eh ?
Also the fault is still present with that LVDS disconnected on the other half of the panel..
I can give more pics of components if needed..
Thanks again.

[tom66]

Re: M421VT LED Screen Color Distortion

LVDS cable runs from main A/V board (with HDMI inputs) to T-con... not from T-con to panel.

[dfang]

Re: M421VT LED Screen Color Distortion

LVDS cable runs from main A/V board (with HDMI inputs) to T-con... not from T-con to panel.

I stand corrected,,told you all I was a novice..
Will check the LVDS from main to T-con..

[dfang]

Re: M421VT LED Screen Color Distortion

Well,,,I disconnected the LVDS Cable & reseated connections .
I have the TV connected to my PC..This is weird,,when the TV is first turned on the pic is corrupted (as seen in pic first post) after about 5 min the pic clears up very nice and stays good so far for about 2 hrs.

[tom66]

Re: M421VT LED Screen Color Distortion

Press and manipulate the cable while the set is running (do not remove it), does the fault change?

[dfang]

Re: M421VT LED Screen Color Distortion

Press and manipulate the cable while the set is running (do not remove it), does the fault change?

Tried manipulating cable with no change..I also shut down and restarted computer after the TV has been working flawlessly for over 3 hrs now,,,and display is still good...Seems like it has to have heat...could the display panel be the culprit ? I will shut down set and give it a cool off period,,,then restart.

[tom66]

Re: M421VT LED Screen Color Distortion

If it is going to be anything it is most likely a main board problem or -possibly- a T-con board problem though I would say main board is more likely.

[dfang]

Re: M421VT LED Screen Color Distortion

I just restarted after a 2 hr cool down and the pic stays bad for about 5 min then clears up.When it's not good,,,the distorted colors pulsate around the objects on screen,,,then it slowly gets less and less becoming perfect

A main board for this is about $100.00 from SJ...Gulp !
Thanks for your help Tom..

[newtothis]

Re: M421VT LED Screen Color Distortion

Use a hair dryer across mainboard... it should clear quicker.... Next time try directing heat at smaller area using insert of toilet roll or similar... Circle smallest area on a pic for us.... May be able to repair

[dfang]

Re: M421VT LED Screen Color Distortion

Will do the hair dryer treatment with toilet roll in hand in the morning concentrating on the main board..Good idea newtothis..I did try hair dryer to heat boards before,,but,,not a concentrated effort on the main...
I think we are on the right path..
I'll be back tomorrow...
Thanks again

[dfang]

Re: M421VT LED Screen Color Distortion

I did some testing with my heat gun and toilet paper roll and came to the conclusion that indeed the main board is the fault. I used compressed air to cool down main board and the picture would go very bad when doing so..If I concentrated the heat on the metal shield,,the pic would clear up in short order.I preformed this test of cooling and heating many times and narrowed it down to what ever is hidden behind the metal shield...So...is there any repair for this board or should I bite the bullet and buy one off the net ?

[newtothis]

Re: M421VT LED Screen Color Distortion

Most likely logic IC under there... from looking at the tracks anyway. Have the equipment to get that shield off?

[dfang]

Re: M421VT LED Screen Color Distortion

Most likely logic IC under there... from looking at the tracks anyway. Have the equipment to get that shield off?

Ok,,got the shield off,,big heat sink under it..Remove heat sink ?

[newtothis]

Re: M421VT LED Screen Color Distortion

Firstly try heat/cold directly at that heatsink

Give is a pic too

[dfang]

Re: M421VT LED Screen Color Distortion

Firstly try heat/cold directly at that heatsink

Give is a pic too

I've done it now! Seems that after I removed the shield on the main board and reinstalled the board,,the TV will not power on...I get 35 VIZIO blinks when it's first plugged in then when I power on,,the VIZIO logo blinks once and that's it,,,Dead duck..I pulled the main back off and looked for a obvious problem,,but don't see anyting..Unfortunately I can't perform further test..I must have done something this main board didn't like..

[newtothis]

Re: M421VT LED Screen Color Distortion

Ok check voltages at PSU - Main connector

[dfang]

Re: M421VT LED Screen Color Distortion

Ok check voltages at PSU - Main connector

Ok,,tomorrow..
Thanks for the help