Vizio M420NV No Picture/No Sound

[mlg1979]

I'm working on my mom's Vizio M420NV. She said it all started the other day when the audio stopped working so she turn the TV off. When she turned it back on it was hit or miss for the picture to stay on. Then finally wouldn't do anything.

My diagnostics so far.....I see not visible damage or anything burnt on either boards. The VIZIO power light at the bottom of the TV is amber colored when off and white when powered on. There is no sound or picture or backlights. I have tested the power supply as much as possible with the tools I have. I have power on the primary side and no real power on the secondary side. If I test the connector going from the power supply to the mainboard the only voltage I have there is 5.3v on pins 1 2 3 which shows to be correct. Pins 8 9 10 are suppose to have 12v but do not.

Is the power supply bad, or do I need to test something else?

Thanks

Mike

[CapLeaker]

Re: Vizio M420NV No Picture/No Sound

If not all voltage rails coming up from the PSU, then you would have to fix that first! Then I am not sure if not something else is going on at the main board.
Check diode D120 on the PSU if it is shorted. That diode rectifies 12V.

[jetadm123]

Re: Vizio M420NV No Picture/No Sound

Your photo is too blurry to make out the writing, but on the power board wiring harness you should have a pin marked something like PS_ON? Appears you have the 5V standby voltage that the mainboard uses, but not the 3.3V signal the mainboard sends to turn on the power supply.

[mlg1979]

Re: Vizio M420NV No Picture/No Sound

I've attached a better pic.

D120 has no voltage, but is that because that half of the board isn't powering up?

The connector that runs to the mainboard the exact voltages are pins 1 2 3 5.3v pins 4 5 6 7 8 9 10 0v pin 11 .5v pin 12 3.2v pin 13 1.7v pin 14 .6v

Hopefully this helps.

[CapLeaker]

Re: Vizio M420NV No Picture/No Sound

check D120 with your DMM in diode test. If it is shorted, it is bad.

[mlg1979]

Re: Vizio M420NV No Picture/No Sound

I removed the diode from the circuit to test, but I'm unable to determine which pin is the gate. Any help is greatly appreciated.

Thanks

[CapLeaker]

Re: Vizio M420NV No Picture/No Sound

no gate. Its a "double" diode. Cathode is in the middle, so your negative lead goes there. Then measure the 2 outside pins. If its a short, its bad.

[mlg1979]

Re: Vizio M420NV No Picture/No Sound

Measures .200 on both sides, so I assume its not shorted. Is that correct? If that is correct where do I go from here?

Thanks again for the help.

[Andrew F. Ali]

Re: Vizio M420NV No Picture/No Sound

I'm not seeing PS_ON pin. Would that be the REMOTE_ON/OFF pin?

[CapLeaker]

Re: Vizio M420NV No Picture/No Sound

What do you get on the remote on/off pin when you turn on the TV? I think the PSU is just off.

[CapLeaker]

Re: Vizio M420NV No Picture/No Sound

You may be able to force the PSU on manually by itself by using a 1k resistor and jump remote on/off to 5.3VSB
That should bring up the 12V as soon as you plug it in. You can take also another resistor, plug in the backlights and jump blon/off to 5.3VSB. That should then bring the whole PSU alive with the backlights on.

[mlg1979]

Re: Vizio M420NV No Picture/No Sound

I did what you said on putting a jumper from 5.3vsb to BL_ON/OFF and REMOTE_ON/OFF and everything works. So I guess that means its not getting signal from the mainboard to turn on. Where do I go from here?

Thanks

[CapLeaker]

Re: Vizio M420NV No Picture/No Sound

Depending on your ability, time, money, equipment etc., either buy a board at SJ or trace and troubleshoot the main board. Maybe a fuse, voltage regulators, caps, diodes etc.

Scroll on top of this thread:
https://www.badcaps.net/forum/showth...999#post300999

[Sauktronics]

Re: Vizio M420NV No Picture/No Sound

I have the same problem wondering if anyone figured out the solutions to this.. If it's just the eeprom that would be great.. Let me know