Vizio D55-F2 backlights won't turn on

[Thiefcatcher]

Hello all! I'm looking for some help in trying to fix my parents-in-law's Vizio D55-F2 tv. The tv will power on, but the backlights won't turn on. I can see a picture using a flashlight and the tv responds to the remote. The audio also works. I have tested all the LED strips and all of the LED's illuminate on every strip when powered from a separate source. I used a multimeter to take voltages from connector CN801 on the power supply board and had the following readings:

TV plugged in, powered off
Pin1-0
Pin2-0
Pin3-0
Pin4-0
Pin5-0
Pin6-0
Pin7-10.06v
Pin8-10.06v
Pin9-10.06v
Pin10-10.06v
Pin11-0
Pin12-0
Pin13-0
Pin14-0
Pin15-0
Pin16-0

TV plugged in, powered on

Pin1-26.55v
Pin2-26.56v
Pin3-26.55v
Pin4-0
Pin5-0
Pin6-0
Pin7-12.66v
Pin8-12.64v
Pin9-12.66v
Pin10-12.64v
Pin11-0
Pin12-0
Pin13-0
Pin14-0
Pin15-2.99v
Pin16-3.36v

Any suggestions on what to replace or test? I can handle probing points with a multimeter and some soldering/desoldering. Thank you in advance!

[neilc6]

Re: Vizio D55-F2 backlights won't turn on

Bit of a non standard configuration because the LED controller is on the main board and not the power supply. There should be a logic signal to turn on the backlight but it will be a trace on the main board and not a pin on the connector. If the backlight isn't coming on and the leds are good, then the main board is suspect if the supply voltages are also good.

[Thiefcatcher]

Re: Vizio D55-F2 backlights won't turn on

Thank you Neil for pointing me in the right direction. I had ordered a main board off of ebay, installed it and no luck. Not being convinced the ebay board was good, I ordered a different main board, installed it and have a working tv again! The in-laws are very happy to have their tv again.

[ajshoe]

Re: Vizio D55-F2 backlights won't turn on

many vendors are confused on this main board. Have to go by the bar code as this is where the part # for the main board is. 75500w01b001 is for the 65" version - 75500w01c001 is the 55" version. The 75500W01C001 will not work in the 65" version as 4 of the 16 led strips will not be lit.

[City Viking]

Your Power supply sounds like it is working correctly. I would look at the main board right where the power comes in. there is a white smd fuse on the board that stops the 24V line. I also spotted a couple other fuses on that board if that isn't the bad one. Here is a video on where that fuse is located: https://youtu.be/DuhcViJ_k3w

Good luck,

City