Vizio VS420LF1A No picture/backlight

[Blackwolf]

Ive got a Vizio VS420LF1A and having an issue with it:
When power is connected, Vizio logo glows orange,
i press power button... the logo turns to white and that's it. I see nothing on the screen, i don't see the back light come on, just a solid white Vizio Logo showing its powered on.
I opened it up and looked for the obvious things like bulging/leaky caps
and everything appears ok.

I also took a flash light and tried to look closely at the panel when it was on to see if i could see anything on the screen (like if the back light wasn't working, but the display itself was) and i see nothing.


Any suggestions on what to look into fixing/replacing would be much appreciated.

[retiredcaps]

Re: Vizio VS420LF1A No picture/backlight

1) Please post clear focused top down view pictures of all your boards following my instructions in my sig file below exactly.

2) Please state if you have a multimeter and are familiar with measuring voltage and resistance?

[Blackwolf]

Re: Vizio VS420LF1A No picture/backlight

Attached are the pictures, I do have a multimeter and I am familiar with how to use it.

Thanks for your help

[tibimakai]

Re: Vizio VS420LF1A No picture/backlight

how about inverter board pictures?

[Blackwolf]

Re: Vizio VS420LF1A No picture/backlight

These are the only 2 boards i see, i do see wires running from the PSU to either side of the panel, Im guessing these wires go to the inverters.
I cant see any easy way to get to them, ill have to take the entire panel apart.
I will try to do that if you think it could be an inverter issue.
Ive repaired sets before that have bad inverters and usually im able to see something on the screen when using a flash light and looking very closely, in this case i cant so Im not sure if its an inverter issue or not but you guys would know much more about this then I so if you recommend i strip it down to get to the inverters i will.

[retiredcaps]

Re: Vizio VS420LF1A No picture/backlight

1) Vizio TVs, for whatever reason, seem to use or have bad voltage regulators.

2) All the red circled components are regulators.

3) List the part number for each.

4) Measure the DC voltage of each pin (ignore the fat tab) for every regulator.

5) Report each part number and readings.

6) The blue circled component is the connector. Measure the DC voltage of each pin and report the legend (what is written on the pcb) and your findings. Pin 14 is your inverter on/off.

[Blackwolf]

Re: Vizio VS420LF1A No picture/backlight

Sorry for the delay in response, I was traveling and havent had a chance to test until today.

The first thing i checked was the connector circled in blue.

Legend is as follows

Pin 1 - PSU on/off
Pins 2 3 4 - +12v
Pins 5 6 7 8 9 - GND
Pins 10 11 12 - +5v
Pin 13 Dim
Pin 14 Inverter on/off

I checked voltage on +5v and it checks out,
however on the +12v line i am not getting +12v. Its reading 0.19v


So im guessing this is the problem, no +12v coming from the power supply.

(I haven't checked the voltage regulators yet, but i will, but im guessing ive found the issue.)

Any suggestions on what to check on the PSU?

[ktulu909]

Re: Vizio VS420LF1A No picture/backlight

See my thread.The main board sends the signal to the PS to tell it to turn on the 12 and inverter lines.

You have a different board than I do,but I would look very closely at the regulators as it turned out to be a single regulator on mine that was keeping it from turning on.

[budm]

Re: Vizio VS420LF1A No picture/backlight

You have power supply with PFC Voltage booster plus inverter. it is all in one board.
Check the DC voltage on that large 450Vdc with the TV OFF, you should read about 165~175Vdc, then turn on the TV, you should see the voltage goes up to about 380~400Vdc if the PFC is working, if it does, that means the PS_ON signal is OK. If not then it can be bad PFC or no PS_ON signal from the main board.
The two inverter transformers on the right of the pictures are driven by MOSTFET's which uses the 380~400Vdc voltage for the inverter circuits instead of the usual 24Vdc power supply.
Can we get the close up pictures of the connectors on the power supply/Inverter board so we can see the labels on them.
By the way, do not run the board without the high voltage wires from the lamp assemblies connected (the two white connectors on the top right of the picture of the power supply/inverter board)

[Blackwolf]

Re: Vizio VS420LF1A No picture/backlight

Ok i read the voltage on the 450vdc
it read 165v in standby, after powering the tv on, it went up to 387v.

Attached is the requested pics

[budm]

Re: Vizio VS420LF1A No picture/backlight

OK, PFC and PS_ON are OK. We will now have to find out why the 12vdc PS not putting out. What do you get at Pin 14 the inverter ON/OFF line?
By the way, we nned real good pictures of the power supply board top and bottom sides, then picture 1/4 section each of the baord that we we can see the deatils of how the traces are connected. I need to trace out where the PS_ON goes to beside the PFC section.

[Blackwolf]

Re: Vizio VS420LF1A No picture/backlight

i get 2.09v when the tv is powered on

[budm]

Re: Vizio VS420LF1A No picture/backlight

That should be enough to turn on the transistor. I will wait for the pictures to trace out PS_ON line and the Inverter on line.

[budm]

Re: Vizio VS420LF1A No picture/backlight

Service manual

[Blackwolf]

Re: Vizio VS420LF1A No picture/backlight

Did you need different pictures then the ones already posted? If so what exactly should i take pics of?

[budm]

Re: Vizio VS420LF1A No picture/backlight

I cannot see the whole board, I need to be able to see the components side, traces on the board VERY CLEARY so I can trace out the connections, without that it will be just impossible to troubleshoot down to component level from long distant. It is like trying to do surgery blindfolded.
Pictures of the whole board top and bottom, and 1/4 section of the board each.
At this point it looks like the problem is in the power supply/inverter baord, but we need to verify first.

[Blackwolf]

Re: Vizio VS420LF1A No picture/backlight

Here are the pics, please let me know if you need any retakes, i tried to do the best i could but my camera isn't so great.

Also just wanted to say thanks for spending your time helping me out with this.

[Blackwolf]

Re: Vizio VS420LF1A No picture/backlight

And heres the rest...

[budm]

Re: Vizio VS420LF1A No picture/backlight

OK, thanks for the pictures, I will download them and see if I can trace out the connections, it will be awhile.

[budm]

Re: Vizio VS420LF1A No picture/backlight

Can you please get the number as printed on the IC circled in red?