Chosen Solution
I was digging around in a dump and found a nice vizio d55u-d1 tv, and figured a simple power board swap would fix it ( it didnt look good). Installed it today and still the same issues. No white power light, nothing backlighting the screen…nothing. Could it be my main board? want to be sure before dropping another 40 on a board. Update (08/03/2020) Ive changed outlets, cables, and the fuse on the power board. Couldnt locate the other ones if there were any, Here i used the chasis for a ground and took a few measurements from the pins
. Seems I dont have blon, but i tested the 5v and got 0 and i tested the 12v (all on dc) mode and got ~19vdc Update (08/03/2020)
picture of ports Update (10/08/2020)
The first replacement was for a 55 inch, so it was wrong, but even the new one inside is giving me NOTHING. not even a
@goochberries420 … i had this exact same set with the exact same problem. the white signal for standby/power on is on the lower right of the front screen. it will light up and fade out. when powered up. this is normal operation. you can change this later in the settings to remain on if you wish. if this doesnt occur, i would check the voltages at the power supply board leading to the main board. there you will have a legend that shows descriptions and voltages. you should have a steady 5 volts stby to indicate power is making its way to the board. if not, check the fuse and the adapter that plugs into the wall. if you have 5v steady at stby. after hitting the on button, the set should turn on the 12v lines. check this. if any of your voltages are off than whats listed on the power supply, you could have a bad replacement. the main board was the issue in my case. the on/off signal was .19v . it needs to be 3.3v. look for on/off and check to see what reading you get. if it is proper voltage, shine a flashlight at the screen about an inch or so at an angle in a dark room. look for any signs of a picture. press the menu button if you have to. post back with the results of these tests for any further assisatnce.
This model TV has a history of main board issues that will give exactly what’s going on in your case where the standby lamp lights when the set is plugged in then fades away and the set is dead after that, unfortunately that board isn’t cheap. The 12 volt supply is actually 19 volts, Vizio has the legend wrong. I’ve fixed several sets with this issue and its always been the main, the power board in this set seldom gives issues. To double check I have a D55u-D1 on my bench that had backlight issues and is fixed now and to be sure I was thinking of the correct model I tested the 12 volt supply and it measures 19.2 volts on a working TV. Also the 5 volt supply is not a standby supply, so will be around 0 with the set off. As the above poster said you need 3.3 on/off voltage to turn the power board on, this set is totally different than most sets that have a 5 volt standby that is always there when the set is plugged in
