Vizio VO42L will not come on

[nvdolfan]

The Vizio emblem is in orange, and turns white when I hit the power button.
On the power supply I have observed that +5VSB is at 5V, PSON is at 0V, and stays there when I hit the power button, A1 is 3.3V when "on", B1 is 5V when "on", otherwise A1 and B1 are 0V. Does that mean the problem is with the main board?
I unplugged the inverter board which had no effect.

What do I need to do to start troubleshooting the main board (assuming that's what the above symptoms point to)?

[nvdolfan]

Little more info... Please let me know if anything else would be helpful... I was going to post better pics once the board problem is a bit more clear.

After reading through all the Vizio posts I saw a lot of references to U33/AMC1117. U33 is an 8 pin chip on my main board so I dismissed that.

F1 and F2 on the main board checked out fine.

TV screen stays completely black when I turn the tv on.

Caps all looked good.

Here is a picture of the overall back of the tv:

[nvdolfan]

Any ideas dgtech or plainbill?
I've been checking the diodes and fuses on the mainboard but everything seems okay. Should I just replace the mainboard or could it be a different board? The geeky engineer in my really want to try and repair but I'm just not sure where to start.
The reason I think it's the mainboard was from plainbill's post in this thread: http://badcaps.net/forum/showthread.php?t=17001

Thanks in advance!

-Chris

[Dgtech]

Do you get any backlights at all?

If no - Check with a flashlight to see if there is a picture in the background.

If yes - Check all of the 1117 LDO's on the mainboard and post the voltages.

Just some basics to get started. There is lots more that you could check and not really what I would check first but... I'm going to bed now. rush rush

[PlainBill]

Originally Posted by nvdolfan

Any ideas dgtech or plainbill?
I've been checking the diodes and fuses on the mainboard but everything seems okay. Should I just replace the mainboard or could it be a different board? The geeky engineer in my really want to try and repair but I'm just not sure where to start.
The reason I think it's the mainboard was from plainbill's post in this thread: http://badcaps.net/forum/showthread.php?t=17001

Thanks in advance!

-Chris

I've been avoiding this type of thread lately. My excuse is I've been busy with outdoor projects now that it's finally cool enough to work outside. But that is just an excuse.

Based on the information you gave, the problem is the main board. And there is the problem. A quick look at the main board shows it to be a typical design with a Standby and Main supply, and a PFC front end. However, there have been a few instances where the labels on a power supply connector ware misleading. In other words, is PSON the control input to the power supply?

A successful repair of a main board is possible, but it is often very difficult to troubleshoot. About the best we can do is check the LDO regulators.

I was reluctant to make suggestions because I'm forced to rely on the information you gave. The pictures don't show the legend on the power supply output connector, and the picture of the main board isn't clear enough to identify possible LDO regulators. So why should I bother?

PlainBill

[nvdolfan]

I see no backlights. Even with a flashlight I don't see anything.
I can't seem to get pictures that are clear enough to read the writing... Will try more tonight. Here is the voltages on the LDO's when the tv is "on" (Vizio emblem turned white). 2 of them don't have input voltage so they obviously aren't regulating but the others seem fine...

LDO's:
U19 G1117 (pin 1 gnd, pin 2 VO, pin 3 VI)
2 - 1.24
3 - 3.85

U21 G1117 (pin 1 gnd, pin 2 VO, pin 3 VI)
2 - 1.24
3 - 2.5

U44 G9117 (pin 1 gnd, pin 2 VO, pin 3 VI)
2 - 0
3 - 0

U22 G1117 (pin 1 gnd, pin 2 VO, pin 3 VI)
2 - 1.24
3 - 3.08

U17 G1117 (pin 1 gnd, pin 2 VO, pin 3 VI)
2 - 1.24
3 - 3.06

U16 G1117 (pin 1 VI, pin 2 gnd, pin 3 V0)
1 - 0
3 - 0

U21 1084 (pin 1 gnd, pin 2 VO, pin 3 VI)
2 - 1.25
3 - 3.03

U20 1084 (pin 1 gnd, pin 2 VO, pin 3 VI)
2 - 1.25
3 - 2.75

Here are the power supply connector pinouts:
Main board cable:
C1 - not connected
B1 - 5V when tv on, 0V when tv off
A1 - 3.1V when tv on, 0V when tv off
+5VSB - always 5V
GND - duh :-)
12V - always 0V
PSON - always 0V

Inverter board:
C1 - not connected
B1 - 5V when tv on, 0V when tv off
A1 - 3.1V when tv on, 0V when tv off
GND - duh :-)
24V - always 0V

[nvdolfan]

Huge thanks to you dgtech and plainbill.
I wound up buying a new main board which fixed my issue.
Now I'll be able to watch Thanksgiving day football in the basement next to my keg fridge!

Thanks a ton.

[rmoody]

You may have noticed that Vizio pumped a lot of these shitty models out there. It's a very common problem with the vo42l and vw42l. Just for kicks, if you get some spare time, open the back and compare ldo voltages from the new board to the old one and see if you can repair it. Never hurts to have a spare laying around.

[Dgtech]

So very true indeed. Although, you never know what parts are stressed now and could be ready to fail on the spare board.

There are certain "Repaired" TV's that I'd keep. Vizio is not one of them. There are too many problems that are known to go wrong with each of the boards inside.