Vizio V042L No Picture has backlights.

[landyboy]

Picked up a Vizio V042L Set powers up as normal. All PSU voltages are correct. Backlight comes on and stays on but no picture. Checked fuses on TCON all are good. No on-screen menu when menu button is pushed.

[tom66]

Re: Vizio V042L No Picture has backlights.

Voltage at each end of fuse?
Checked voltage regulators?
Once turned on, can you turn the set off from the remote or power button?

[landyboy]

Re: Vizio V042L No Picture has backlights.

Yes voltage at both ends of fuses. And yes you can turn the set off using the remote and keypad. Do you mean the voltage regs on the main? Here are some pics.

[tom66]

Re: Vizio V042L No Picture has backlights.

Yep check the regulators on the main board.

[landyboy]

Re: Vizio V042L No Picture has backlights.

v15 2.076,3.324,5.110
v16 12.35,0,5.021
v17 2.078,3.324,5.110
v20 0.555,1.806,3.289
v21 0,1.257,2.507
v22 2.092,3.142,5.157
v44 8.44,9.69,12.35

[landyboy]

Re: Vizio V042L No Picture has backlights.

sorry all U's
U19 1.256,2.508,5.117

[budm]

Re: Vizio V042L No Picture has backlights.

v22 2.092,3.142,5.157: This is bad, 3.142-2.092 = 1.05V, the difference always be 1.25V (+/- 3% or better)

[landyboy]

Re: Vizio V042L No Picture has backlights.

Sorry re-tested U22
2.080,3.334, 5.157

[landyboy]

Re: Vizio V042L No Picture has backlights.

I also tested F1 on TCON and only have .228 VDC is that correct?

[budm]

Re: Vizio V042L No Picture has backlights.

The DC voltage on the T-CON fuse should be either 5v or 12v depends on the T-CON board design. So 0.228V on both ends of the fuse? If that is the case, then the MOSFET on the main board is not getting the voltage to it or it is not being told to turn on to supply the volatge to the T-CON board. You need to trace out that supply line on the main board.

[landyboy]

Re: Vizio V042L No Picture has backlights.

yes .228 both sides. I will try to trace the circuit,

[landyboy]

Re: Vizio V042L No Picture has backlights.

U37 the 8 pin has 12.38 volts on 4 pins on one side and 0.228 on the other side. This is where I get lost a little. I am assuming that is where the 12v supply to the TCON goes through.

[landyboy]

Re: Vizio V042L No Picture has backlights.

Sorry Here is pic

[tom66]

Re: Vizio V042L No Picture has backlights.

Part # of U37?

[landyboy]

Re: Vizio V042L No Picture has backlights.

4953GM

http://www.alldatasheet.com/view.jsp?Searchword=4953GM

[tom66]

Re: Vizio V042L No Picture has backlights.

OK what do you see on pins 1 (S), 2 (G) and 7 or 8 (D). I think they have put the two FETs in one package in parallel. Note pin #1 is marked by a dot, and the pins are counted from end to end, down, and then end to end. (Refer to datasheet if unsure.)

[landyboy]

Re: Vizio V042L No Picture has backlights.

1 (s) 12.35
2 (G) 12.30

Both 7 and 8 0.236

[tom66]

Re: Vizio V042L No Picture has backlights.

OK, this indicates the main board is not turning on the T-con power supply. G should be less than 8V or so to turn on the T-con power. Try checking the voltages on Q26 (directly below U37) but I think you need to swap the main board (probably corrupted firmware/EEPROM.) Typical Vizio. Basically 99% main board failures.

[landyboy]

Re: Vizio V042L No Picture has backlights.

.655 bottom left

0.00 Bottom right

Top Pin 0.026

[tom66]

Re: Vizio V042L No Picture has backlights.

OK, that should be working... Hmm. Looks like the main CPU is sending the "ON" signal (>0.6V) after all.

Try placing a wire jumper from pin 1 to pin 8, then turn set on. Does T-con get power? You may still have a blank screen. You might be able to leave this jumper in place, since the T-con is usually always on whenever the set's main power supplies are on. The switch FET might be included to help in sequencing the start up so the screen doesn't flicker on power on/off.