Vizio VW42LHDTV10A No power

[lilleap3]

I recently just dug up a Vizio 42" LCD tv out of my sisters basement where it had been stored for about a year. Problem is the tv is getting no power. The vizio symbol on the front of the tv does not light up at all. So I've been doing a lot of reading and this forum seems like the place to get answers or atleast ideas about the problem and how to go about fixing it.

[PlainBill]

Re: Vizio VW42LHDTV10A No power

I recently just dug up a Vizio 42" LCD tv out of my sisters basement where it had been stored for about a year. Problem is the tv is getting no power. The vizio symbol on the front of the tv does not light up at all. So I've been doing a lot of reading and this forum seems like the place to get answers or atleast ideas about the problem and how to go about fixing it.

That is correct.

PlainBill

[cmj21973]

Re: Vizio VW42LHDTV10A No power

Go to Elektrotanya.com and search for the service manual. Read pages 31-33 and decide if you are willing and able to take it apart.

Follow the links at the bottom of PlainBill's post on how to take pictures and attach them. Post good pictures of all the boards, top and bottom.

I tried to post the manual myself, but it failed to uplaod.

[lilleap3]

Re: Vizio VW42LHDTV10A No power

Alright I took it apart and here are the pictures. If you want closer pictures or a picture of a certain area let me know. I've also read the service manual and I think U8 is probably the problem.

[PlainBill]

Re: Vizio VW42LHDTV10A No power

Alright I took it apart and here are the pictures. If you want closer pictures or a picture of a certain area let me know. I've also read the service manual and I think U8 is probably the problem.

Good (but not great) pictures. It's especially nice that you didn't crop off corners, etc.

You idea that U8 might be the problem is interesting. The LDOs in that area (especially U33) are one of the known causes of problems, although the symptoms don't match.

If you don't mind, I'd like you to verify a few points.

With the boards in place and all cables connected, power plugged in, please measure the SVSB voltage (CN5, any pin 10-12), use any pin 5-9 (SGND?) as the ground point. Also, what is the voltage on pin 1 (PSON)? Try pressing the power button. Does the voltage on pin 1 change? Is there any voltage on any 12V pin (2-4)? (Note: When I specify a group of pins, it is only necessary to measure one of them).

PlainBill

[lilleap3]

Re: Vizio VW42LHDTV10A No power

Alright it took me awhile to dig up my multimeter but I did like you asked and I got some interesting results. For pins 10-12 I got 5.23 volts but for the pins 2-4 and pin 1 I got 0 volts on everything even after pushing the power button. I can't say my power button pushing was 100% though pushing the button while holding the multimeter and reading it wasn't easy. So what does this mean? The J7 connector is bad?

[PlainBill]

Re: Vizio VW42LHDTV10A No power

Alright it took me awhile to dig up my multimeter but I did like you asked and I got some interesting results. For pins 10-12 I got 5.23 volts but for the pins 2-4 and pin 1 I got 0 volts on everything even after pushing the power button. I can't say my power button pushing was 100% though pushing the button while holding the multimeter and reading it wasn't easy. So what does this mean? The J7 connector is bad?

OK, lecture time. The power supply is two supplies in one; standby and main. The standby supply is on whenever the power cord is plugged in. It provides power to a small section of the main board - the standby processor, the remote sensor, and the control buttons. When the standby processor gets the 'Power on' signal form either the remote or the power button it performs a few rudimentary tests and turns on the main supply by pulling CN5, pin 1 up to about 3.3 volts. That obviously isn't happening.

The next step is to check the main board. If you look at the picture which includes the tuner (the silver box with the coax connector on it), on the lower edge of the picture is the connector which connects to the power supply. Just above that connector are F1 and F2. With power disconnected, check the resistance of each of those fuses. It should be less than 1 ohm on the 200 ohms range. Alternatively, you can check the voltage at each end of both fuses with the main board connected to the power supply, and the power supply plugged in.

PlainBill

[lilleap3]

Re: Vizio VW42LHDTV10A No power

Alright I checked the resistance like you suggested and as you said I did get about .9-1 ohm on F1 but for F2 I got nothing the meter didn't move. Man, this forum is definitely the place to find help and to learn. So what's my next step?

[retiredcaps]

Re: Vizio VW42LHDTV10A No power

[QUOTE=lilleap3;162857I did get about .9-1 ohm on F1 but for F2 I got nothing the meter didn't move.[/QUOTE]

F2 is bad.

[lilleap3]

Re: Vizio VW42LHDTV10A No power

Alright, that's what I figured. I'll look for a replacement part here in town and if I can't find one locally I'll use the sites I've seen recommended on the forum. Any ideas on why the fuse would have failed in the first place? If there is another problem that caused the fuse to blow I'd like to fix it also. Also thanks a bunch for all the help. I like to build computers, take things apart and learn how they work but locating a single fault or problem on a board is a new area for me.

[PlainBill]

Re: Vizio VW42LHDTV10A No power

Sometimes (rarely) fuses blow for no obvious reason. What are the markings on the fuse? I might be able to suggest a substitute for test purposes.

PlainBill

[lilleap3]

Re: Vizio VW42LHDTV10A No power

The only markings on it are LF 3A. So its a 3 amp fuse and I'm guessing 125 volts.

[cmj21973]

Re: Vizio VW42LHDTV10A No power

Does the LF it look like this one?
If it does then it was made by Littlefuse Inc.

Photo from Digi-Key

[PlainBill]

Re: Vizio VW42LHDTV10A No power

This is probably a Littlefuse series 454 Nano fuse. At $1.62 each, they are a little pricey to be blowing while troubleshooting.

The first step is to measure the resistance from each end of the fuse to ground. It should read in excess of 10 ohms. If it does, it's time to CAUTIOUSLY apply power. There are two ways to do this. Far and away the best is a bench supply withe adjustable voltage and current limiting.

Most people don't have them on hand. The other approach is to use a small automotive lamp such as the 1157 tail light. Wire that across the fuse, then hook everything together. If the light bulb starts glowing (dimly, the supply is only 5 volts), there is a problem on the board. If it doesn't, measure the voltage on the load side of the lamp. If it is 4.5 volts or higher, try turning on the TV.

PlainBill

[lilleap3]

Re: Vizio VW42LHDTV10A No power

Hey guys sorry for the delay, I had to travel on sort notice for almost 2 weeks. Thankfully I ordered those fuses before I left and when I got back the day before yesterday I installed a new on and I'm happy to say the TV works great. Thanks for all the help I really appreciate it.

[daimoku]

Re: Vizio VW42LHDTV10A No power

Great! Glad to hear!

[MisterD]

Re: Vizio VW42LHDTV10A No power

I have the same model Vizio, that will not power on, the vizio on the front lights up orange. I only have 5 volts on the power supply, the other 12 v and 24 v have no reading, my question is: If it won't power on should I get the 12v and 24v readings in standby mode or only if the set turns on? Thanks in advance.

[budm]

Re: Vizio VW42LHDTV10A No power

The 5v standby is an always on power supply that runs the minute you plug the TV into the outlet. The 12V/24V is turn on by the main board that sends the PS_ON to the power supply to turn on the 12v/24v section.
So please post the pictures of all the board and closed up pictures of the connectors so we can read the labels on them so we can tell you which pin to test, please use GO ADVANCED and use the attachment function to upload the pictures.

[MisterD]

Re: Vizio VW42LHDTV10A No power

Here are some pictures, I also should say that the PSON pin 1 has absolutely no voltage either, so I'm only getting the 5v standby and when I try to power it on nothing happens, I checked both fuses on the motherboard and they are good but the 3.3 v that is required for the PSON is not present, Is it possible to apply 3.3v to the PSON pin connector without unhooking any connectors to see if the set will then power on? or can that cause damage to other components?

[MisterD]

Re: Vizio VW42LHDTV10A No power

Here's one more picture.