Vizio V042L FHDTV10A No Video but has sound

[Mrlinshadowdale]

Hi,

New to the forum so any help you can provide would be great. I have a the TV listed in the description and it started acting up. I power it on and video shows up for a second or so before turning off. The right side of the TV has normal video which then seems to fade to black on the left side of the TV. This leads me to believe that one of the inverter boards is damaged. I've been looking for schematics and service manuals however I cant seem to find any for this model, and doesnt have a download link on the page. Again any help would be greatly appreciated.

[retiredcaps]

Re: Vizio V042L FHDTV10A No Video but has sound

and doesnt have a download link on the page.

Others have run into this problem using other browsers.

Use IE8 for elektrotanya.com and the get manual icon will show up and let you download.

[Village Electronics]

Re: Vizio V042L FHDTV10A No Video but has sound

Hi,

New to the forum so any help you can provide would be great. I have a the TV listed in the description and it started acting up. I power it on and video shows up for a second or so before turning off. The right side of the TV has normal video which then seems to fade to black on the left side of the TV. This leads me to believe that one of the inverter boards is damaged. I've been looking for schematics and service manuals however I cant seem to find any for this model, and doesnt have a download link on the page. Again any help would be greatly appreciated.

I just finished one this morning. Looks fine. You probably do have an inverter board problem. I'm going by memory because the one that I just repaired is put together and waiting to be picked up.

Memory tells me that this uses a master/slave configuration and the problem is often the IC's on those boards. Take the covers off the boards and look for damage to the ICs. Perhaps a tiny hole. If I remember correctly the boards have 4 MOSFETs each. They may read a low resistance across. That is a good indication that the IC is bad. Don't change the MOSFET until you remove the IC.

[Mrlinshadowdale]

Re: Vizio V042L FHDTV10A No Video but has sound

I tried using internet explorer 8, to no avail unfortunately. Is there anyway someone could upload it for me? I've attached a picture of the loaded website as well just so you can make sure I'm not being a moron or something. I'm going to disassemble it in a couple of hours and take a look at the boards, I'll make sure upload correct pictures of the inverter boards as well as resistance measurements of the MOSFET's

[retiredcaps]

Re: Vizio V042L FHDTV10A No Video but has sound

Look lower (or use search on your IE). See red circled area.

[Mrlinshadowdale]

Re: Vizio V042L FHDTV10A No Video but has sound

Wow, glad I got that pointed out to me, thanks.

[Mrlinshadowdale]

Re: Vizio V042L FHDTV10A No Video but has sound

Ok, I've taken the tv apart and im pretty sure that its the slave inverter board. I've confirmed that the power supply is functioning normally (5V standby on all the time and 24 VDC to both inverters when powered on), the master inverter has a blue LED that lights up when the power button is pressed and you can see the backlight turn on on the master side. The slave side does not turn on. I've confirmed power is being received, I cant locate the LDO for housekeeping supplies but the test points show 5.047V and 3.748V when measured so i'm pretty sure they are functioning. I've uploaded pictures of slave inverter board, there are no obvious problems with it. The second picture has the pins labeled here are the resistance values associated with the measurements.
Q1 Q2 Q3 Q4
1 to 2 285K 290K 40.4 100K
1 to 3 284K 298K 8. K 80K
2 to 3 8.49K 8.5K 8.5K 8.5K

As compared to the master inverter board Q3 and Q4 values are a little off. Im not sure where everyone did their measurements however. It seems to me that the either Q3 or the driver ic is damaged as the input to the gate of a FET should be very high resistance. I also measured the voltage across the transformers during operation and confirmed that there was no voltage across the slave side. Any thoughts?

[Dgtech]

Re: Vizio V042L FHDTV10A No Video but has sound

Just for the heck of it, check the master board as well. By the way, the slave board does not have an LED on it. Only the Master lights up.

[Mrlinshadowdale]

Re: Vizio V042L FHDTV10A No Video but has sound

I did check the master board as well. That was what i used for a baseline value :-). The resistance values of the master board are as follows:
Q1 Q2 Q3 Q4
1 to 2 285K 290K 280k 292k
1 to 3 284K 298K 280k 280k
2 to 3 8.49K 8.5K 8.5K 8.5K

[Mrlinshadowdale]

Re: Vizio V042L FHDTV10A No Video but has sound

I've got both of the inverter boards in the lab today and I'm planning on powering them both up using a bench supply. Im going to assume that the flex cable supplied the PWM control for the CCFL brightness so i'll need to mock that up as well. The goal is to see if the driver IC is actually driving the MOSFET's correctly and to do a comparison between the master and slave circuits. I did notice last night, however, that when i was tinkering around with the master inverter that the only time it worked was when i had the chassis ground connection through the mounting points. I find it curious that the 24VDC return is not used for this purpose. Could you guys give me any suggestions on how to setup the ground scheme? Also what should I use for a load on the transformers? Thanks again for all your help.

[Dgtech]

Re: Vizio V042L FHDTV10A No Video but has sound

I would do a much easier test that that. I'd simply remove the two in question (Q3 and Q4). Then test them individually out of circuit. With them removed, I'd check the board resistance on the same pads as well. If you check the board and still get the same bad readings, then it most likely is the driver chip. If when you check Q3 and Q4, they show the same bad reading, then it's definitely each of those components.

[Mrlinshadowdale]

Re: Vizio V042L FHDTV10A No Video but has sound

I shall do just that, I wanted to use the good board to confirm my findings. Which it did. The master board however still exhibits the same behavior that it did in the tv, namely it turns itself off after about a second. Any ideas as to why that would be? I dont want to replace all of the chips on the slave only to have the problem still exist.

[Dgtech]

Re: Vizio V042L FHDTV10A No Video but has sound

These boards work in conjunction with each other. This is the usual behavior for this problem. I have noticed that whenver there is a problem with the master board, usually the light doesn't work at all. These boards share the same voltages however there are some differences with the master. I can't tell you how it does what it does or where the sensing circuit for the backlights is but I do pickup on trends of problems I see. I have seen this problem in Philips sets and Vizio sets. There are a lot more name brand sets with this same exact problem. LG is one as well.

[Mrlinshadowdale]

Re: Vizio V042L FHDTV10A No Video but has sound

Ok, so I got it working again, the problem was with the built in regulator on the driver IC. I noticed it was floating ~1VDC instead of the 5VDC. It was a simple chip replacement and the TV booted right up. Thanks for all your help everyone.

[falax41]

Re: Vizio V042L FHDTV10A No Video but has sound

Mrlinshadowdale,

I believe that I have the same trouble as you did. Which pins on the IC did you use to test the voltages? The input is 25VDC, but there are many outputs... I have no idea what they are supposed to be...

Thanks...

[GbreadMan]

Re: Vizio V042L FHDTV10A No Video but has sound

Fsm, hth.

[stp715a]

Re: Vizio V042L FHDTV10A No Video but has sound

Ok, I've taken the tv apart and im pretty sure that its the slave inverter board. I've confirmed that the power supply is functioning normally (5V standby on all the time and 24 VDC to both inverters when powered on), the master inverter has a blue LED that lights up when the power button is pressed and you can see the backlight turn on on the master side. The slave side does not turn on. I've confirmed power is being received, I cant locate the LDO for housekeeping supplies but the test points show 5.047V and 3.748V when measured so i'm pretty sure they are functioning. I've uploaded pictures of slave inverter board, there are no obvious problems with it. The second picture has the pins labeled here are the resistance values associated with the measurements.
Q1 Q2 Q3 Q4
1 to 2 285K 290K 40.4 100K
1 to 3 284K 298K 8. K 80K
2 to 3 8.49K 8.5K 8.5K 8.5K

As compared to the master inverter board Q3 and Q4 values are a little off. Im not sure where everyone did their measurements however. It seems to me that the either Q3 or the driver ic is damaged as the input to the gate of a FET should be very high resistance. I also measured the voltage across the transformers during operation and confirmed that there was no voltage across the slave side. Any thoughts?

Hi. Are these readings taken in circuit or out? In circuit I am reading the 8.5K on all mosfets pins 2-3 but megohms on all the other measurements (1-2 and 1-3).

[Dgtech]

Re: Vizio V042L FHDTV10A No Video but has sound

This is your first post on this set right?? What symptoms are you having with your set?

[stp715a]

Re: Vizio V042L FHDTV10A No Video but has sound

This is your first post on this set right?? What symptoms are you having with your set?

Yes. First post. Symptoms are power on, sound, then power off by itself within a few seconds.

[Dgtech]

Re: Vizio V042L FHDTV10A No Video but has sound

do you have any backlights at all?