Vizio M501i-B1 - Tries to turn on over and over but can't.

[Cam.anderson22]

So I've done quite a bit of research on vizio's not having power or not turning on. I haven't found anyone with my specific problem yet. It tries to turn on over and over again, but it never fully boots up. The white led on the bezel comes on and then dims out, and the red/blue led comes on on the main board. This repeats every 45 seconds or so. It finally came on in the middle of the night after about a week of this cycle, but now I can't get it back on again. None of the caps seem bulged either.

Power supply Model 715G6100-P04-003-002H.
Main Board Model: 715G6815-M02-000-005N.

I've metered the voltages coming out of the power supply, and I get what should be expected.
19.74v on hot rails
5v good
12v good
24v is 19.74v
PSON is 3v
Dim is 3v
On/Off is 0.06v when trying to turn on, 0v on standby
Large caps at bottom of board are at 393v

Question is, which board should I replace? Does this sound like a main board or a PSU problem?

Thanks in advance!

Pic of the back of the tv
https://drive.google.com/open?id=1r9...KlVODJIg1GNjRA

[budm]

Re: Vizio M501i-B1 - Tries to turn on over and over but can't.

The main board is not sending the BL-ON (ON/OFF) to turn the backlights.
Are you sure that getting 19.74V instead of 24V?

[Cam.anderson22]

The main board is not sending the BL-ON (ON/OFF) to turn the backlights.
Are you sure that getting 19.74V instead of 24V?

Yes, 19.74v going to MB and LED driver board.

[Cam.anderson22]

Re: Vizio M501i-B1 - Tries to turn on over and over but can't.

Any ideas? There's a multi wire going from the MB to the led driver board, and only one pin has voltage on it (12v). All the other pins are zero.

[budm]

Re: Vizio M501i-B1 - Tries to turn on over and over but can't.

"On/Off is 0.06v when trying to turn on, 0v on standby"
Right now the main board is not sending the ON Voltage to turn on the backlights circuit.
You may be able to simulate the ON/OFF signal by using the 1000 Ohms resistor between the STBY 5V and the ON/OFF pin, BUT YOU MUST DISCONNECT this wire going back to the main board first.