Vizio xvt472sv - PSON Always has Voltage

[jeebuzzin]

With TV is plugged in and NOT pressing the power button, PSON already has 3.16v and the PS is switched on providing 5v, 12v, 18v, & 24v. The power switch is not stuck closed and is showing 2.29v across it when pressed.

Although the PS is switched on, there are no backlight or picture present, just a dim white Vizio logo. The picture and light may be a separate issue? But why is the PSON signal always on?

Thanks for any help!

Main Board
F1 5.10 5.12
F2 12.02 12.02

L271
G9117
U2 2.05 3.30 5.10
U4 0 1.24 3.30
U6 6.86 8.11 12.02
U7 2.06 3.32 5.08

L391
G1084
U3 2.05 3.30 5.08
U5 2.04 3.29 5.08


Power Board Connectors
PSON 3.16
+5VSB 5.16
12v 12.02
18v 18.16
24v 24.31

[jeebuzzin]

Re: Vizio xvt472sv - PSON Always has Voltage

Follow up info:

L354
G1084
U9 (backside of mainboard) .55 1.81 3.29


LED Driver board
Both main fuses good and passing 24.3v

[jeebuzzin]

Re: Vizio xvt472sv - PSON Always has Voltage

Set aside the PSON always on and further diagnosing the no picture finds that the T-con board is getting no power. Following another thread on here (thanks jasonpeters!) I found U33 not turning on. Jumpered with a resistor to GND it turns on and now have 11.9 to T-con, but no difference...no pic or backlight.

Has anyone had the issue with the PSON being activated as soon as you pug the TV in? Can someone point me in a direction to start figuring that part out?

T-con Board
Main Fuse - good (11.9 v when U33 on)

[budm]

Re: Vizio xvt472sv - PSON Always has Voltage

Unless you have the diagram for this main board then it will be real hard to troubleshoot down to component level as you see in the other thread (https://www.badcaps.net/forum/showthread.php?t=49276).
May be it is EEPROM problem.
Beside PS-ON is stuck, you also missing the BL-ON, the On command for powering the T-CON, no LVDS signals feeding the T-CON.

[jeebuzzin]

Re: Vizio xvt472sv - PSON Always has Voltage

Thanks for the reply. I have been searching for a diagram for it as I see jasonpeters needs it too, but coming up dry. Looking more and more like just replacing the mainboard, but they are pretty rare it seems.

[jasenpeters]

Re: Vizio xvt472sv - PSON Always has Voltage

jeebuzzin, thanks for the "props". But, I couldn't get as far as I did without "panda" Budm.
He's an awesome mentor and guide.

In my case, I too jumpered U33 to ground using a 820ohm resistor. And the TV has worked ever since (5 days). I can't tell you why though. I really never confirmed a failing part.
The "jump" seemed to bring it back to behaving normally.

I'm still tracking down a schematic and will make it available as soon as it's acquired.

I would not give up, though. That's a very good TV. I think the main board is definitely worth the after market price (hopefully under $100). Of course, only if that is where the problem is.

shop jimmy does not have it in stock it seems.
But, someone here on the forum may have a working spare. I'm sure there's a "for sale" section somewhere on the forum or there may be other affordable sites that carry it.

[jeebuzzin]

Re: Vizio xvt472sv - PSON Always has Voltage

I won't give up, I'll stow it away with the others I've collected from friends, family, or such. I have a pile of about 10 or so TVs that I am finally getting around to tinkering with.

I've searched all over the net and there are none of these mainboards to be had, but worst case, maybe I'll offer up the remaining parts of this one for another needy soul.

If you do find that schematic, def post it up.

Best of all, this project led me to this forum.....a valuable resource indeed!

[CoppellTVRepair]

Re: Vizio xvt472sv - PSON Always has Voltage

Just for the record, most of the times when a main board starts automatically (BL_ON activates almost instantly) 99% of the time the problem is in the main processor, which never actually starts up properly.

Seen it happen many times on various boards and for some reason always with MediaTek MT processors as opposed to, say, the Broadcom BCM ones.

- bobby