Vizio M420NV

[nomursy]

Hi and thanks for taking the time to offer your assistance. I have a 3 y/o Vizio M420NV that was working a few nights ago and then would not turn on in the morning. The orange Vizio light is on, but will not turn white when the power button is pushed on the side of the TV or with the remote. I tried the system reset (unplug for a while, hold power button on TV x 30 sec, plug in) with no change.

I don't have any experience with circuit boards at the level I've been reading about on this forum, but I have picked up some basics from various posts and reading the stickies.

After reading a lot of posts and talking to Vizio's out-of-warrenty repair company, I concluded (without any real evidence to back it up) that either the power board or main board was the culprit. I opted to buy a new power board to see if that would be the easy fix. I installed it tonight with no change in my situation.

So, here's where I stand now….

I have a new power board installed. With the TV plugged in, I read 12V on pins 8-10 (on the power board at the connection coming from the main board) and 3V on pin 11…all other pins had no readings. With the power button held down and then after it was released, there was no change in voltage at pin 11 (which I understand to be the point where the main board tells the TV to turn everything on…in very simplistic terms).

I don't see any bulging caps on either board. I have an analogue multimeter and it's resistance selectors are either Rx10 or Rx1K. I tried testing the only thing I knew was a fuse on the power board (unplugged, selected Rx10) but saw no needle movement on either power board. I'm thinking, but not sure, that the 10x mag on the resistance is too much to be able to check the fuse.

That's all the data I have. I'll try to attach pics of the boards. Thanks again for any input you have.

[budm]

Re: Vizio M420NV

There are two fuses (F1, F2 next to the white connector to the left of the board) on the main board that you should check to see if it has dc voltage reading on both ends of the fuse with ref. to the chassis ground.

[nomursy]

Re: Vizio M420NV

I believe both fuses had DC voltage on both sides of the fuses. Just to make sure I did it right, here's what I did. Multimeter set to DCV 50. Neg to ground screw where the ground wire at the power plug in is attached. Red to each side of the fuse. The reading for the F2 fuse was twice as high as the F1 fuse (if I am reading the right line on the meter, the needle went to 55-60 on F2 and 25-30 on F1)

[budm]

Re: Vizio M420NV

I think you need to get Digital meter first, I am not sure what you are seeing on your meter. To it sounds like you have 5.5~6V on F2, and 2.5~3V on F1.
I expect one of the them to be 5V (for logic circuit) and another one to be 12V (for sound amplifiers).
Per picture, CN201 has pins for 5.3vstby and pins for 12V. Do get 5.3V at the CN201?

[nomursy]

Re: Vizio M420NV

I think I was reading the wrong line of the meter and I did get 12 and about 5.3 at the fuses. I checked the pins on what I think is labeled CN202 (not 201?) and got 5.3 at pins 1-3 and 12 at 8-10. I'm trying to attach a pic of the meter reading one of the fuses.

[nomursy]

Re: Vizio M420NV

Does anyone have any other ideas of what could be going on? Thanks again for all the help.

[Shane711]

Re: Vizio M420NV

I have this problem with this TV. Same main board. The TV was working but was having trouble turning on after being off and the HDMI's were not working. I changed the EEPROM and now the TV will not turn on. I have not been able to figure out the problem.

[budm]

Re: Vizio M420NV

I have this problem with this TV. Same main board. The TV was working but was having trouble turning on after being off and the HDMI's were not working. I changed the EEPROM and now the TV will not turn on. I have not been able to figure out the problem.

So what happen if you put the old one back in?

[Shane711]

Re: Vizio M420NV

I put the old EEPROM back and the TV will not turn on. I am trying to figure out what happened, not sure if I caused something else to go bad. But since others are having the same problem maybe it is not my fault.

My friend has the same TV with a bad panel(Lines) so I plan to use it to fix the one I have. I will test both TVs to see if there is a difference in voltages between the 2.