Vizio M3D460SR

[bobbyd40]

Hi I am looking at this Vizio for a friend.It works fine for a while then all of a sudden back light turns off and audio is still going.I can see with a flash light that video is there.If i turn it off and back on back light is on and picture as usual.I understand that there is a light sensor that turns back light on and off does anyone have a diagram of its location?

I do see a small board coming off the main board that has a black wire going to top of frame with what looks like some kind metal strip or thermal element.posted a pic of the board and the little dielectric element thing.

Another note it does have the high pitched whine that is posted about the vizio But that is not a concern.

Thanks

[bobbyd40]

Re: Vizio M3D460SR

Another thing i noticed is that it seems to happen during a scene change or while changing channels.

[tom66]

Re: Vizio M3D460SR

The sensor is most likely for backlight dimming, not for on/off control, and it'll make the backlight brighter in a bright room, not darker.

[bobbyd40]

Re: Vizio M3D460SR

OK this is a weird one. I looked at all boards and caps look fine.Also checked all connectors and reseated them.I see nothing obvious wrong. I forgot to mention this is a LED.

[tom66]

Re: Vizio M3D460SR

Full LED, or edge LED?

[cliff_hootarski]

Re: Vizio M3D460SR

That small module looks like a BlueTooth transceiver.

[bobbyd40]

Re: Vizio M3D460SR

Edge LED.Yes your right it is a blue tooth.

I think i have found the problem .I noticed in settings that back light brightness was maxed at 85% i set it at 50% and no cutting off picture looks better too.I rest it back to 85% and starts cutting out again.Reset it back to 50% and watched all last night and left on and still working fine.I wonder if at 85% it is to much and over working something and shutting down?

I am going to run for several hours more and if no problems give it back.

[bobbyd40]

Re: Vizio M3D460SR

Even at 60 and 70% it does not cut off.I thing i will leave at 50% to be sure.

[tom66]

Re: Vizio M3D460SR

Probably an issue with the PSU being unable to supply power to the backlights.

[bobbyd40]

Re: Vizio M3D460SR

Probably its a pretty chintzy looking TV inside compared to a lot of others i have looked at.
If it works and functions at those settings i think i will leave well enough alone and return to owner and call it a day.

[tom66]

Re: Vizio M3D460SR

Can you show us a picture of the whole chassis and one of the PSU?

[bobbyd40]

Re: Vizio M3D460SR

sure

[tom66]

Re: Vizio M3D460SR

Wow, I see what you mean. Pretty bare power supply. Looks cheaply made.

[bobbyd40]

Re: Vizio M3D460SR

Very cheap and small everything.Guess its how they get them so slim.

[bobbyd40]

Re: Vizio M3D460SR

Bent over caps to save space too.

[bobbyd40]

Re: Vizio M3D460SR

Still going fine to no back light loss so far been running for hours and hours. beginning to think power supply just not big enough to run back light at max brightness for to long before it over loads it and turns them off.

[bobbyd40]

Re: Vizio M3D460SR

Well i was wrong, today it shut off back light.I started putting light pressure on the psu with no change back light stayed on.Then put light pressure on LED driver inverter board and back light shut off,so i re started TV and pressed on board again around center just below mosfet and back light shut off.
Now back light comes on for about 20 seconds and goes off.I did not crack board or anything only put very light pressure on it.So now i am wondering if the problem lies in the LED driver board.

[bobbyd40]

Re: Vizio M3D460SR

I see pics are bad here is re post of pics.

[tom66]

Re: Vizio M3D460SR

Check the voltage across those two longest rubycons - Care high voltage - I expect maybe 90~150V.

[bobbyd40]

Re: Vizio M3D460SR

Update:Applied pressure to LED driver/inverter board and could turn back lights off at will. Ordered new board and installed and TV working fine now.After checking into it further found that solder joints for Q852 most likely bad or Q852 itself after heating up.

So Vizio LED with random back light turning off,re solder Q852 if that doesn't work change Q852 or board.
Thanks for all the help on this one.