vizio 42 gv421 no picture/sound

[tom66]

Re: vizio 42 gv421 no picture/sound

Yes, the PSU converts 115V AC mains into DC 5V, 12V and 24V through several complex stages.

Are you using the chassis of the TV as your ground?

[TimT]

Re: vizio 42 gv421 no picture/sound

the last test i did not use the chassis.. I have a large metal press that I used. should I have used the chassis?

[tom66]

Re: vizio 42 gv421 no picture/sound

You should use the chassis. If the metal press is earthed and so is the TV (most are), that can work, but it will be more accurate to use the chassis of the TV as your earth reference. For now we only need 5VSB, as it would appear something is up with it.

[budm]

Re: vizio 42 gv421 no picture/sound

If you use the chassis as ground and the voltage still reading bad, then try changing this starting cap.

[TimT]

Re: vizio 42 gv421 no picture/sound

I am going to retest with the chassis as ground. what should 5VSB be at? thanks everyone for your help!

[tom66]

Re: vizio 42 gv421 no picture/sound

5VSB should read around 5V. Anywhere from 4.8 to 5.2V would probably be fine.

[TimT]

Re: vizio 42 gv421 no picture/sound

retested with chassis as ground. and will use that from now on..
PSON 0 when plugged in but powered off. would jump to 3.10 when i turned power on " backlight came on ". 5VSB was 5.5 powered off or on.

[budm]

Re: vizio 42 gv421 no picture/sound

OK, that means the main board is at at least sending the PS_ON and at the BL_ON OK to the power supply board.
Next voltage to check will be the voltage on the surface mounted fuse on the T-CON board which is under the metal shield sitting on the top center of the screen with multi-pin cable attached to it, check and see if you have either 5vdc or 12vdc on both ends of the fuse.
Examples:
http://s807.photobucket.com/albums/y...-TCON%20board/

[TimT]

Re: vizio 42 gv421 no picture/sound

not sure were it's located on my board. are there any markings i should look for? I see F1 and F2 im assuming F= fuse.. marked on the picture

[budm]

Re: vizio 42 gv421 no picture/sound

That is the main board picture, you need to look at the T-CON board as I indicate in post 28.

[TimT]

Re: vizio 42 gv421 no picture/sound

I opened the T-CON cover.. I tested fuse F1 @ 0.14 but I noticed another fuse??? see picture it stands out! looks bad?? tested 0.60 on one side 0 on the other

[tom66]

Re: vizio 42 gv421 no picture/sound

The other device isn't a fuse, it looks like it might be a ceramic capacitor of some sort, it is normal for them to come in lots of different shades.

Since you have 0.16V at T-con fuse, it's not receiving the correct supply (5V or 12V.)

[budm]

Re: vizio 42 gv421 no picture/sound

So there is no voltage at the fuse? There is a switched transistor/MOSFET on the main board that turns on when TV is power up to supply the power to the T-CON board.
Need good closed up picture of the main board where the cable to the T-CON board is connected.

[TimT]

Re: vizio 42 gv421 no picture/sound

I will take a close up of that connection. I just noticed there are two " fuses " on the mainboard were the cable from power board connects. this cable comes from the same pins i tested yesterday POSN and 5VSB. the fuse F1 reads 12.77 on one side 0 on other powerd on. see picture

[tom66]

Re: vizio 42 gv421 no picture/sound

Great! You found the fault. That 12V fuse is blown. Can you get hold of a 3 or 5A small-blade automotive fuse? You can use that very temporarily in place of the existing blown fuse. If the blade fuse blows again, something else is wrong on the main board.

[TimT]

Re: vizio 42 gv421 no picture/sound

i will check real quick! I will pull one from my car if i have to lol

[tom66]

Re: vizio 42 gv421 no picture/sound

Just solder wires to it and solder it across the blown fuse. Use something that's not important of course -- like the radio!! Goes without saying not to touch the ABS, or lights.....

[TimT]

Re: vizio 42 gv421 no picture/sound

ok got that working! 12v on both ends.. used 5A fuse. have no head lights now.. just kidding.. now on the T-CON board i was getting 0.04 on fuse f1 im now getting 12v on both ends. i attached picture but still not working.

[tom66]

Re: vizio 42 gv421 no picture/sound

I gotta get up early for lectures tomorrow, but I'll leave you with a test to make (not my video):
https://www.youtube.com/watch?v=cNFzBJELFoU

Different problem, but the voltage regulator failure causes lots of odd issues.

[TimT]

Re: vizio 42 gv421 no picture/sound

thanks for your help! that video helped alot. looks like the same part is bad on mine. regulator amc117 reads 1.95 on tap then 5.9 0 1.2 then i checked more they seem to drop down the last one i tested was 1.7 on tab 1.9 1.08 0 so looks like i need to order some parts.