Vizio SV420XVT1A LCD 2 Seconds to Black

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

These are the readings from J1 its a little cryptic,
Board Definitions:
Pins : Label
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:
Results:
Pins : Results
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

I will look over everything again. Following the path the best I can. I have some of the reading for U14 and U17 from last night in my notebook but as soon as the system got worse I did not post. I will post those up when I get home.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Ok so I guess it's time to start from zero. So I want to make sure that the power board is working, how would I test that without the main board? I think that I read somewhere that if I jump pin 1 (ps on/off) with one of the 5v pins with a 3.3k resistor it should power up? Did I read that correctly or is there something else I can do?

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

What do you get at pin 1 the PS_ON PIN? It should be around 2.5~5v range when you hit the power switch, it you do have the voltage, then it means the board is talking to the Power supply board.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

It goes between .03 and .04, I seems the boards are not talking with each other anymore.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

I have a main board coming on monday so it will be interesting to see if that gets be back to where I was in the beginning.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Sorry for your bad luck on the board.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Well it was probably something I did and I chalk it up to learning so we shall see what Monday brings.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

So I picked up the 3.3k resistor to check the power board this weekend to make sure that the power board is up and running before I put in the new Main board on monday.


Quick question since this resistor will be bypassing the main board and i wont need it hooked up there are two plugs in the upper left hand corner of the board should I leave those plugged in when testing or is that something I can remove?

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Those are the high voltage wires to the backlights assemblies, you must keep them in place or you will get real big arcing if the backlights inverter kicks on and may cause damages to the inverter circuits

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

I will make sure that they are plugged in when testing thanks. will update with results.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

My replacement main board is out for delivery, so I will have that installed tonight and I will be picking up a 3.3 resitor to test the power board first to see when this gets me. Hopefully the replacement baord will resolve issues or atleast get me back up on the right track.

Will post results later

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

OK so i installed the new Main board and I am now back where I started. So just a refresher. Plug in vizio symbol turns amber. Press power, vizio turns white and then backlight comes on. 2 Seconds later backlight goes out. Vizio light stays white. Power button functions like normal.

So the question is what could be the issue? I will be retesting all voltages again to verify but if its like last time everything was good leaving the main cable to main main board. Meaning I had 5v, 12v and 24v leaving that cable. I am new at this so is there something else I should be testing?

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

So we are back to the original problem before the main board was damaged.
What do get at pin 14 of J1 for Inv ON/OFF? It sounds like the inverter section is bad (bad Inverter Transformers, MOSFET's for Inverter transformer driver, bad CCFL).
Post #21
"These are the readings from J1 its a little cryptic,
Board Definitions:
Pins : Label
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:
Results:
Pins : Results
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"

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Here is Pin 14 with power on.
Pin14:4.3v

Here are the new readings:

Power Off

Pin10:5.1v
Pin11:5.1v
Pin12:5.1v


Power On:

Pin1:2.4v
Pin2:11.6v
Pin3:11.6v
Pin4:11.6v
Pin10:5.1v
Pin11:5.1v
Pin12:5.1v
Pin13:2.8v
Pin14:4.3v

Pin 13 is the one pin that changes from once power is hit to the current on.

It goes from 0 to 3.3v then steadies at 2.8v

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

The Inverter ON/OFF is the one I am interested in and it is good. So now we need to dig deep to find out why the inverter section does not stay on.
On the two inverter transformers, please take the resistance reading on pin 3 and 4 to see if they read the same, also take the resistance reading of the 4 small blue caps close to where the lamp wires are attached to.

[cashkennedy]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Your original problem which is now back is most likely a problem with the inverter as budm just said.

The initial way to test this is with the power disconected you want to test resistance on both of the 2 large black transformers on the top left of the power board. They should have huge pins soldering themt o the board that youll see fromt he back, and there should be at least 2 pins on 1 side, and another 2 on the other side that lead to those wires to the bulb (pink and white). You want to test resistance on both pairs of pins, for both transformers. If your unsure where to measure, then send a picture of the back side of the power supply board closeup on where the 2 black transformers are soldered.

Attached is your closeup picture of the 2 transformers.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Meter set at 200
Top Transformer pin 1,2:0.5
Top Transformer pin 3,4: 27.5
Bottom Transformer pin 1,2:0.5
Bottom Transformer pin 3,4: 26.8

Blue Caps:
TopLeft: .89 set at 20M
TopRight: 27.7 set at 200
BottomLeft:26.9 set at 200
BottomRight:4.13 set at 20M

Those reading are with power unplugged. Let me know if those meter settings are right. I bascially changed resistance until I got readings.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

"Blue Caps:
TopLeft: .89 set at 20M
TopRight: 27.7 set at 200
BottomLeft:26.9 set at 200
BottomRight:4.13 set at 20M"

They do not sound right.
"TopLeft: .89 set at 20M
TopRight: 27.7 set at 200
BottomLeft:26.9 set at 200"

Can you remove and measure them.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Here are the numbers off the blue caps:
Top left:27j 6kv 080
Top right:47j 6kv 08d
Bottom left: 47j 6kv 08d
Bottom right: 27j 6kv 080

So that seems that I should get the same readings for TL and BR. Also should be same for TR and BL. Or maybe I am interpreting that incorrectly.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

When you measure these caps out off the board, make sure your fingers do not touch both probes other wise you will be reading your body resistance. These cap should read open circuits, the meter should show over range reading.
They are 27pF 5% (J = 5%) 6000V, and 47pF 5% 6000V high voltage ballast caps, if you can read resistance with your meter (your meter can put out 9v maximum), just think what will happen when these caps are exposed to 2000v.