Vizio SV421XVT will not power on, no backlight, no click when powered on

[ncweasel]

I acquired a broken Vizio SV421XVT LCD this week from a colleague who said it turned off while watching tv. It will not power on by power button on set and the backlight does not come evident by looking down through vent holes on top edge of the set. also the Vizio logo on the front of the set does change from orange to white when plugged in. I have visually inspected both circuit boards (power board and main board) on the tv and I see no blown fuses, no bulging or oozing caps or any other signs (brown or burnt) of a short or overheating.

I found the service manual on this forum and followed the "trouble of DC-DC converter" troubleshooting flow chart page. The J1 connector was tested by plugging in power and grounding the black lead on my tester to the chassis of the tv and placing the red lead on the hard wires on the back of the receptacle part of the connector that go from the connector to the board ( is this correct?)

Here are my readings:
J1
P10- 18.25 v
P11- couldn't get to it
P12- couldn't get to it

J1
P2-11.71v
P3- 0v
P4 - 0v

U1
P06B03LVG
AND6L1E02
P5- 5.08v
P6- 5.08v
P7- 5.08v
P8- 5.08v

U2
P1611C
1117
P2-5.06v

U3
P1611C
1117
P2-5.06v

U5
L353
G1084
P2-5.06V

U9
L353
G1084
P2- 3.29v

U7
P1611C
1117
P2- 3.29v

U4
P1611C
1117
P2- 1.24v

U6
P1611C
1117
P2-8.15v

U10
L404
G5927
P7-1.08v

I am thinking i have a bad power supply board since J1 Pins 3 and 4 are reading 0v. please let me know if i am headed down the right path and if further information is needed. thanks..!!

[ncweasel]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

I sure would like some feedback on my issue and troubleshooting I have done so far. I know the experts are busy but I would appreciate some help. Please let me know what I have left out of my original post if possible. thank you so much.

[Caleb]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

While I am not an expert by any means, according to the flow chart you should have 5v standby on that first set of pins, 18v is way too high. I would suggest you retest to make sure it wasn't an erroneous reading. If it still is 18v then it would indeed suggest the power supply is faulty. Also make sure to test with set both off and on. The logo changing would suggest that the standby voltage is functional.

It may be that the flow chart was for a different model revision than yours. There should also be a silkscreen next to the power connectors identifying which pins should have which voltages. if you cant get to the probe to contact the pins I often use a small piece of 24 gauge wire pushed into the top hole of the connector to test a specific pin. I can see the metal inside the connector on your pictures so you should be able to stick your probe right in there. I might be helpful to have a pic on the other side of the power connector where it show the voltages as well as know what the center of the board reads I can make out 5v and 12v, the third looks like it may say 18v, if that is what it says the 18v you have may be what its supposed to be.

Vizio's are also known for eeprom corruption which causes similar symptoms. Hope this helps you on your way to fixing this set.

[tom66]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

I'd check the battery in your multimeter is good, a low battery can cause wildly incorrect readings.

[ncweasel]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

thank Caleb, I will double check my readings after replacing battery in my MM (thanks tom66)

[ncweasel]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

I have replaced battery in my multimeter and have reread voltages. Set will not turn on so testing was done with power plugged into set. here are my results again:

J1
P10- 18.25 v
P11- 18.26v
P12- 0v

J1
P2-11.71v
P3- 0v
P4 - 0v

U1
P06B03LVG
AND6L1E02
P5- 5.08v
P6- 5.08v
P7- 5.08v
P8- 5.08v

U2
P1611C
1117
P1-2.05v
P2- 3.30v
P3-5.06v

U3
P1611C
1117
P1-5.07v
P2-3.28v
P3-5.06v

U5
L353
G1084
P1-2.04v
P2-3.28v
P3-5.06V

U9
L353
G1084
P1-.54v
P2-1.78v
P3- 3.29v

U7
P1611C
1117
P1-2.04v
P2-3.29v
P3- 5.06v

U4
P1611C
1117
P1-0v
P2-1.24v
P3- 3.26v

U6
P1611C
1117
P1-6.87v
P2-8.15v
P3-11.70

U10
L404
G5927
P1-5.06v
P2-.78v
P3-0v
P4-.79v
P5-3.84
P6-0v
P7-1.08v
P8-5.08v

attached is a picture of the silk screened values on the power connector (CN201)and here are my readings from it:
(Label-reading)
Standby-2.67v
12v-12.08v
12v-12.08v
GND-0v
GND-0v
GND-0v
GND-0v
GND-0v
ST\+5V-empty
ST\+5V-5.15v
ST\+5V-5.13v
ST\+5V-5.15v
DIM1-0v
DIM2-0v
INV ON\OFF- 1.75v

I am really confused as to which board is bad. After first testing I thought that the power board was bad since Pins 3,4,12 on J1 were reading 0v. Now after retesting it I am also seeing that U3 and U4 don't look right, I am thinking main board is bad..!! or could both be bad?? I see in some threads with similar or exact tv where they tested the voltage on the PS_ON, where is this?

sorry for all the questions but trying to fix a tv is new to me, obviously. thanks for all the feedback.

[ncweasel]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

I just did more reading on this forum and discovered valuable information on interpreting the voltage regulator readings I made. I now think U3 and U4 are within specs and are fine. now I am back to thinking power supply is the culprit. I also removed power supply board from tv to inspect the bottom and I don't see any noticeable signs of "damage".

[ncweasel]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

here are 3 more pictures; overall board layout, bottom side of main board and power supply.

anyone have any more comments on my analysis??

[aaronwt6]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

Are these reading with the main board connected or disconnected? I would expect the standby pin to be closer to 5V and the INV ON to be closer to 3V. Unplug the main board completely from the power supply. Then, connect the power cord and take the readings again.

After that, we can force on the power supply to see if the backlights come on and then proceed from there.

Based on my experience with Vizio TVs, I'm guessing its the main board but lets make sure.

[aaronwt6]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

Could you also post a picture of both connectors going from the PS to the main with the cables unplugged? I'm counting 15 labels but 16 pins. One of those has got to be the PS-ON pin but I don't see it. It's seems obvious that the PS is getting turned on though because you are getting 12V and 18V outputs on the connectors.

Is there indeed 16 wires coming out of that connector or only 15?

[budm]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

"Standby-2.67v" That is the PS_ON signal. You should see this voltage changes state when you turn the TV on and off, same for the inv_on/off.
See if they change state or not first, if not, then the problem is on the main board.

[aaronwt6]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

Upon further inspection I believe the PS ON is below that INV ON pin. Seems you have a wire there that isn't labled. Again, please check all 16 pins with the cable unhooked and post results.



Edit: Budm is probably right. However that inverter on/off voltage seems way to low to me. What you are going to need to do is jump from the 5V pin to both the STBY and the INV ON with the main cable unhooked. If you get backlights at that point then the main is bad. Pretty typical for Vizio.

[ncweasel]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

10-4. I will follow all suggestions, take more photos and post results tonight. thanks for your feedback.

[aaronwt6]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

Here's the thing. If you force on the PS and the backlights and the screen lights up you are just about guaranteed it's the main at that point. I mean there's always a chance you have multiple issues but Vizio main boards are absolute crap.

[budm]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

The PS_ON or BL_ON can be as low as 1.5V as you can see in my diagram. So verify using force on to see if it will come on.

[aaronwt6]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

The PS_ON or BL_ON can be as low as 1.5V as you can see in my diagram. So verify using force on to see if it will come on.

Nice. Didn't realize it could be that low and still function. I guess it could feasibly be a backlight issue. ncweasel, have you tried shining a flashlight on the screen when you power it up to see if you can make out any sort of image?

[ncweasel]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

Nice. Didn't realize it could be that low and still function. I guess it could feasibly be a backlight issue. ncweasel, have you tried shining a flashlight on the screen when you power it up to see if you can make out any sort of image?

thank you for the input yesterday but I didn't get a chance to take a look at recommendations yesterday but will tonight.

aaronwt6, I am little confused by your last question about shining the flashlight on the screen.
Are you saying plug power cord in (so it has power) and then shine flashlight on screen to check for images (i assume with some sort of video input source or am i looking for vizio logo or something else?) even though it doesn't "power up" when I push the power button?

[aaronwt6]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

Well, given your voltage readings it seems the main is telling the PS to turn on. That's why I brought up the flashlight test. Even if the backlighting doesn't work you should be able to make out the Vizio splash screen or no input message after it starts. If you can't, it points to an issue other than just the backlighting. The fact that you said the logo changes from orange to white indicates that the set is at least partially functioning.

As far as unplugging the connector from the PS to the main....If you do that, verify 5V is connected to both the standby and the BL_ON, and still have no backlighting, then you are pretty much guaranteed a power supply issue.

If you try that and get backlighting, then its almost certainly the main. I'm voting main on this one simply because it's a Vizio. Although I've had a couple with bad PS's too.

[ncweasel]

Re: Vizio SV421XVT will not power on, no backlight, no click when powered on

Here are my findings on questions asked by BudM and Aaronwt6:

Aaronwt6:Unplug the main board completely from the power supply. Then, connect the power cord and take the readings again.
Answer: STB=0v, INV ON=0v

Aaronwt6:Is there indeed 16 wires coming out of that connector or only 15?
Answer: only 15 wires

Budm:"Standby-2.67v" That is the PS_ON signal. You should see this voltage changes state when you turn the TV on and off, same for the inv_on/off.
See if they change state or not first, if not, then the problem is on the main board.
Answer: "Standby-2.67v" didn't change when I pressed power button on/off.

Aaronwt6:What you are going to need to do is jump from the 5V pin to both the STBY and the INV ON with the main cable unhooked. If you get backlights at that point then the main is bad
Answer: jumped a 5v pin to STBY and a separate 5v pin to INV ON and I didn't see any backlight. I did the flashlight test.