Vizio M420NV no backlight

[nomoresonys]

Re: Vizio M420NV no backlight

There's some other things you can test on the mainboard, looks like you need to know why the mainboard isn't sending the bl_on signal.

[sricechex]

Re: Vizio M420NV no backlight

Thank you for finding that video. I haven't gotten to the unit this evening yet, I'll keep you posted.

[budm]

Re: Vizio M420NV no backlight

If you can force the backlights on using the resistor, then you can disconnect just the BL-ON signal wire going back to the main board and put all the connectors back in place, and then keep the pull-up resistor for the BL-ON pin on the power supply board in place, power up the TV and everything should then work normally if the BL-ON signal is the only problem on the main board.

[sricechex]

Re: Vizio M420NV no backlight

Nothing happens when I disconnect the motherboard from the power supply and plug in.
In regards to the resistor test in post #8, my board lists no "PS_ON," as far as I can see. Are any of these other pins indicators of a ps_on?

[sricechex]

Re: Vizio M420NV no backlight

The backlights do come on with a 1k between BL_ON and 5VSB!

[nomoresonys]

Re: Vizio M420NV no backlight

Ok, you could test some of the components on the mainboard if you want to dig deeper, where to start is the question.

[sricechex]

Re: Vizio M420NV no backlight

This tv is certainly not worth a $100 mainboard ($25 pawnshop special), but in that I got it just for the learning, I'm tempted to swap the eeprom, if I can have some confidence that a failed eeprom is the culprit.
Any thoughts on further testing on the mainboard?
I greatly appreciate your input, nomoresonys and budm. You guys are kind to lend your expertise

[nomoresonys]

Re: Vizio M420NV no backlight

I'll try to help but it will be slow, not too good with troubleshooting mainboards.

[nomoresonys]

Re: Vizio M420NV no backlight

If you trace the bl_on wire from powersupply back to mainboard so you know which pin it is, unlpug connector at mainboard and see what voltage you have there, I always unplug tv first then unplug connector from mainboard then plug tv back in, to try not getting any strange surges.

[nomoresonys]

Re: Vizio M420NV no backlight

https://www.techwalla.com/articles/h...-board-of-a-tv
Rough guide on mainboard testing.

[sricechex]

Re: Vizio M420NV no backlight

Great, dude, thanks. I'll let you know if I learn anything useful for future projects!

[nomoresonys]

Re: Vizio M420NV no backlight

https://www.youtube.com/watch?v=Sghh8BK5zIw Testing video, looks like hes testing eprom voltages, voltage regulators etc.

[nomoresonys]

Re: Vizio M420NV no backlight

https://elektrotanya.com/?q=keres Put your model number in there, see if they have a service manual.

[nomoresonys]

Re: Vizio M420NV no backlight

Vizio 32 inch (VA320M) Eco 1080p black screen
There's a thread there by KuDaH with some info.

[nomoresonys]

Re: Vizio M420NV no backlight

There's quite a few threads on this model, put M420NV in the search up there on this page.

[budm]

Re: Vizio M420NV no backlight

Did you try post #23?

[sricechex]

Re: Vizio M420NV no backlight

Budm, that's what I did this morning, and the backlights work great! Ran off my Raspberrypi just fine. Thanks for the input.
I had only a minute before work, so haven't been able to play with the other posts yet. I want to see if I can gain some experience isolating the culprit component(s) with some more precision.
If it promises to be too frustrating or expensive, I'll just jam that resistor back in.

That will keep my sunk cost at $25.01...not too shabby.

[budm]

Re: Vizio M420NV no backlight

So all the TV functions are OK then?
We can use other signal as the BL-ON.

[sricechex]

Re: Vizio M420NV no backlight

I haven't made time yet to try all functions, just menu functions, and successful HDMI input. When I get back to it I'll try different input and audio.
Are you thinking of any specific functions?
Where would you suggest sourcing the other signal?

[budm]

Re: Vizio M420NV no backlight

You can use T-CON ON signal for BL-ON.