Vizio E421VA LCD - no backlight, no image

[Eric_Flash]

Any help much appreciated.
Vizio E421VA - LCD

Black screen - no image using flashlight method. Standby powers on, logo lights up when plugged in. No sound. No obvious burnt components. No swollen caps. CPU does not seem hot.

Power supply connector - Power off - voltages
Standby - 5.2
Standby - 5.2
PS/On - 0
24v - .1
24v - .1
Gnd (3) - 0
12v -.1
12v -.1
P DIM - 0
On/Off - 0

Power supply connector - Power ON - voltages
Standby - 3.7
Standby - 3.7
PS/On - 3.0
24v - 25.2
24v - 25.2
Gnd (3) - 0
12v - 12.4
12v - 12.4
P DIM - 2.5
On/Off - 0.1

The On/Off at 0.1v seems suspicious. I'm not sure, but I think this supposed to tell the Power Supply to send voltage to the inverters(?)

Other data, if it helps.
Connector CN4402 - T-Con board, with power on:
Gr - 12.4
Yel - 12.4
Or - 0
R - 0
Br - 3.6
Bl - 3.6

Data cable on T-Con - no voltages on any of the lines.

Disconnecting both T-Con power and data cables and cycling power made no difference.

The 2 single wires that run from the Power Supply to the inverters (?) - no voltage.

I'm assuming that there's something wrong with the main board, but no one has them in stock. So I'll try to fix at the component level.

What should I check next?

[budm]

Re: Vizio E421VA LCD - no backlight, no image

"On/Off - 0.1"
You are correct, the main board is not sending the on command to turn on the backlights circuit.
Without schematic of the main, all you can do is visual inspection, Voltage testing on the regulator IC's, try to locate switch Transistor for the BL-ON signal.
You can also force on the backlights by disconnecting the BL-ON wire going to the main board first then use 100 ~ 500 Ohms (any Wattage be fine) resistor between BL-ON and 3.3VSTBY to simulate the BL-ON signal, then you can verify if all the TV function are OK or not, we want to make sure BL-ON is the only problem the TV has.

[Eric_Flash]

Re: Vizio E421VA LCD - no backlight, no image

Well I'm stumped. I'm finding it impossible to locate any bad components. Of course, I'm not very skilled, and get lost pretty quick following traces. I tried to force the backlights on by jumping STBY and BL-ON, but they didn't come on.

Is it possible that the main board is shutting off the BL-ON signal because the CCFLs are bad?

[budm]

Re: Vizio E421VA LCD - no backlight, no image

Well I'm stumped. I'm finding it impossible to locate any bad components. Of course, I'm not very skilled, and get lost pretty quick following traces. I tried to force the backlights on by jumping STBY and BL-ON, but they didn't come on.

Is it possible that the main board is shutting off the BL-ON signal because the CCFLs are bad?

But did you disconnect that BL-ON wire going back to the main board first before jumping BL-ON wire to Standby power supply output pin?

[Eric_Flash]

Re: Vizio E421VA LCD - no backlight, no image

Yes, I popped out the respective wire from the connector

[budm]

Re: Vizio E421VA LCD - no backlight, no image

Yes, I popped out the respective wire from the connector

Well, the power supply/inverter combo board will require more in-depth troubleshooting then.