Vizio SV420XVT1A LCD 2 Seconds to Black

[Crimsonmt]

Hey everyone I am new to this so please bare with me. So a little background. I received this TV from a co-worker that was just going to throw it away so I decided to take it and try and fix.

Symptoms: I plug in the TV and the Vizio symbol turns Amber. I press the power and the Vizio light turns white. The backlight comes on and about 2 seconds later the backlight goes out and the Vizio light stays white.

I looked over the board and did not see and obvious blow caps. So I tried to read up on what to test and this is where Im at.

Attached are the photos that I took:
Entire assembly with covers off
Power Board
Main Board
Audio Board
And one other board I dont know (the one in the upper left of the full image) and help please.

So some basic testing I have done:

Once the TV is on no backlight and white Vizio symbol I took these readings:
The main cable from Power Board to Main Board
1: PS On/Off
2,3,4: 12v
5,6,7,8,9: Ground
10,11,12:5v
13: Dim
14:Inv On/Off
15:VBRA
So I took readings going into main board and they are as follows:
2,3,4: 11.68v
10,11,12: 5.07v
14:1.06v
*when power button is pressed it spikes to 3.28
15: 4.30v

Power Board to Audio Board:
24.06v over both wires.

From this it seems that the power board is working.

Next I have read through many threads trying to learn so I took some other readings of:
u16, u45 which are AZ7805T-E1 825D16
and
u19,u21,u22,u15 which are L032 G1117

How I tested I used black probe on TV ground/screw and then red probe on each post. Hopefully I did it right please correct me so I can learn.

u16:
vI:2.81v
G:.01v
vO:1.47v

u45
vI:3.24v
G:.03v
vO:2.08

Tested these same black probe on ground/screw and red probe on post left to right (1,2,3)
u15:
1: 2.06v
2: 3.30v
3: 4.99v

u19:
1: 1.26v
2: 2.50v
3: 4.98v

u21:
1: 0.0v
2: 1.24v
3: 3.31v

u22:
1: 4.92v
2: 3.30v
3: 2.06v

I also took readings for u33, since that seems to be a commong issue with Vizio Tv's
I did the same test black probe to screw and red probe to left side posts.

Diagram:
5678
||||
[--]
||||
1234

1: 4.91v
2: 4.91v
3: 4.92v
4: 4.93v
Now to test 5-8 I connected Red probe to 4 and then black on each post 5-8.
voltages remained same.
4,8: 4.93v
4,7: 4.93v
4,6: 4.93v
4,5: 4.93v

I am new to this so I could have taken those wrong but like I stated above I want to learn. So anyone that can assist me and help me get this TV fixed would be great.

Sorry for the wall of text but everything is fresh in my mind so I wanted to get it all down.

Let me know what my next step is or if you have seen this issue please let me know. Also let me know if I am missing something that you need to assist

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

The power board is a combination power supply and Backlights inverter board all in one.
The possibilities can be bad inverter transformers, inverter transformer drive circuits (MOSFET), bad DC feeding the inverter circuits (bad caps, etc.), bad CCFL.
Try this first, measure the DC voltage on that large 450vdc cap, measure it right on the legs of the cap, it should be around 380~400Vdc when TV is on.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Powered on the TV and tested the large 450vdc cap and it was 391vdc.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Good, the power supply for the backlights inverter is OK.
Since the backlights did come on for seconds, then next thing we need is a good closed up pictures of the top and bottom side, you should also take good closed in 1/4 of the board at the time so we see all the details how the traces are connected.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

I will pull the power board and main board and get close up pictures of them top and bottom in 1/4 sections. Will post tomorrow once completed.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Look to see if you notice any burnt/damaged components also.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Nothing looks burnt/damaged and I will get my pics up.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

When I get home I will update with photos, on a side note I dont know if this harmed me more but when I was testing the voltage of the circled piece (see imaged attached) my red probe slipped off the first post and basically connected post 1 and 2. As soon as it did the backlight came on and I reacted and pull the red probe away and backlight went out again. Not wanting to do it again I have been extra careful but I thought I would bring it up just in case it helps or if I completely just jack things up more.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

It does matter if the Backlights does stay on and no going out after 2 seconds, if it does come on when the probes touch and STAY ON as long as the probes still making contact, then it means the Backlights inverter is OK but the command signal that turns on and off the Backlights may be the problem. Is there any label on the power supply board that shows "BL_ON"?
That part looks like voltage regulator IC.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

By the way, here is the service manuals:

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

So would it be okay to test that connection again to see if the system comes on and see if the menu comes up on the screen? Or could that cause more issues?

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

By the way, here is the service manuals:

Thanks I will look that over today and follow the charts, it looks like the best one to follow is the DC-DC converter steps. But it cant hurt to run through them all just for learning knowing what the results should be and if that part is in working condition.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

I will have to look at the serivce manual on how the Backlights is commanded to turn on.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Nothing looks burnt I unsoldered and resoldered the 2 transformers, to solder joints are the best so that will be the first thing people will pick out. Attached are a lot of pics of power board top and bottom

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Now posting pics up Main board top and bottom

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

More Bottom of Main pics

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

So I was going through the service manual and was going through the DC-DC tests. Well i was checking Fuse1 now nothing is working. I still have standby 5v but front Vizio logo blinks white. No 12v or 24v. So now I am worse off than I started. Now quick question if something was failing not completly toasted yet and that was part of the first symptoms and then I did something at put it over the edge. Could that even happen or did I just make everything harder?

I am going to go do some research on the Blinking White Vizio Logo.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Are you talking about F1 on the power supply board? Sounds like something got damaged.

[cashkennedy]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

I believe he is refering to f1 on the main board. Because if f1 on the power board went bad he would get not be getting the vizio logo blinking.

On these boards, (its really similar to the vx32l that im having trouble with), f1 on the main board handles all the 5v comming into the main board from the power supply, if f1 on the mainboard goes bad you will not get the vizio logo to light up, as the LED's are driven off of 3.3v power converted down from the 5v.

So most likely his neither boards F1 is bad, because if either was blown you wouldnt get the vizio logo to light. How are you testing f1? should set your multimeter to resistance, and as long as both sides of the fuse are less then 10 ohms resistance then its still good.

On a side note, just from probing around on my vx32l, i blew the f1 and had to replace it. If you did blow it you can jsut solder a small strip of wire across the top so that you can keep testing the set until you get a new fuse to replace it.

If you go to a step and it failed the step, and it said 1) check f1, and 2) ..., your problem might be whatever the second sugestion indicates.

[cashkennedy]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

BTW, from the readings you posted very early on, your U15, 19, 21, and 22 all seem to be fine.

You didnt post readings on J1, U14, U17 yet, so hopefully you can post the readings on the pins the dc-dc checklist asks you to check.

U16 i think outputs variable voltages for the tuner to use, so is most likely not your problem.

Based on past cases, probably one of the 1117 regulators is bad, U33 though in your set is not the same as in the smaller models, the equivalent part in your model is one of the 1117 regulators.