Vizio LED Driver

[Kaveman42]

My Vizio P502UI-B1 TV has no backlight and from what I can tell no image. The TV power indicator turns on for a few minutes then begins flashing for about 30 seconds then turns off. I've tested Power board and that looks good. Even changes the eeprom, but that didnt help. One thing I noticed is that the LED driver board has no power going to the LED plugs. In my image, I can see there is power on the green connection/capacitors but I get no power on the red connections/capacitors. Is it safe to say that the led driver board is bad? Anything else I can check before ordering a new board?

[Kaveman42]

Re: Vizio LED Driver

Thought I'd also mention that if the TV is left plugged in, the power indicator comes on then begins to flash then turns off. It keeps doing this until I plug it in. Sometimes I have even heard audio coming from the TV, but not always.

[neilc6]

Re: Vizio LED Driver

You need to check if you are getting PS-ON and BL-ON signals from the main board and if all your voltages are good.

https://www.badcaps.net/forum/showthread.php?t=76708

[R_J]

Re: Vizio LED Driver

Check if you get +5 volts on CN805 pin 9 of the driver board, all the other pins on cn805 are clock/data lines
Do you get any voltage on L801,2,3 or 4 when the tv is first turned on, that should be the boosted led voltage.

[Kaveman42]

Re: Vizio LED Driver

You need to check if you are getting PS-ON and BL-ON signals from the main board and if all your voltages are good.

https://www.badcaps.net/forum/showthread.php?t=76708

I don't see anything labelled BL-ON. But I get 2.9V for PS-ON.

Check if you get +5 volts on CN805 pin 9 of the driver board, all the other pins on cn805 are clock/data lines
Do you get any voltage on L801,2,3 or 4 when the tv is first turned on, that should be the boosted led voltage.

PS-ON = 2.9v
BL-ON = Don't see anything labelled BL-On

cn805
Black - 0
Brown - 0
Red - 3.1v
Orange - 0
Yellow - 0
Green - 0
Blue - 0
Purple - 4.9v
Grey - 0.05v (pin 9)
White - 12.14v


cn801,2,3,4 = 0v


It looks like the issue may be with CN805 pin 9 since I'm only getting 0.05v. What should I be testing from here?

[R_J]

Re: Vizio LED Driver

What is cn801,2,3,4 =0v ? Does CN805 pin9 connect to the main board?
Check the voltage on ZD801 anode and D865 cathode, check if C8027 is shorted?

[neilc6]

Re: Vizio LED Driver

Checking the power supplies on shopjimmy, there should be an ON/OFF pin which should be the backlight control pin.

[Kaveman42]

Re: Vizio LED Driver

What is cn801,2,3,4 =0v ? Does CN805 pin9 connect to the main board?
Check the voltage on ZD801 anode and D865 cathode, check if C8027 is shorted?

cn801,2,3,4 is:
cn801
cn802
cn803
cn804
They all have 0v on all pins, so no power is going to the LED's.


ZD801: 24.3v and 4.3v
D865: 4.03v and 0.05v
C8027: Not shorted

[Kaveman42]

Re: Vizio LED Driver

Checking the power supplies on shopjimmy, there should be an ON/OFF pin which should be the backlight control pin.

There is one labelled On/Off and DIM, but neither are connected to anything. Might be because this TV supports dynamic back light, which is probably controlled by the motherboard. Here is a picture from Shopjimmy of the board.


https://assets.shopjimmy.com/media/c...425xb6-top.jpg

[R_J]

Re: Vizio LED Driver

I had asked if you had any voltage on L801,2,3 or 4.
If ic801 is a aoz1268, pin 2 is the enable pin, see if it connects to cn805 pin 9

[nicholas1110]

Re: Vizio LED Driver

Hi, this model commonly has no backlight symptom. Many people try the eeprom as they are sold on eBay and a lot of them available. We just repaired 3 of these models last week all same symptom and all same fix. Failed bga solder on main board. To fix it properly you will need to reball the bga on the main board. To test the theory you can heat the chip alittle and see if your symptom changes. Hope this helps and saves you from buying unneeded parts.

[Kaveman42]

Re: Vizio LED Driver

Hi, this model commonly has no backlight symptom. Many people try the eeprom as they are sold on eBay and a lot of them available. We just repaired 3 of these models last week all same symptom and all same fix. Failed bga solder on main board. To fix it properly you will need to reball the bga on the main board. To test the theory you can heat the chip alittle and see if your symptom changes. Hope this helps and saves you from buying unneeded parts.

Where is the BGA located on the mainboard? I've already tried replacing the eeprom but no luck.

[diif]

Re: Vizio LED Driver

Where is the BGA located on the mainboard? I've already tried replacing the eeprom but no luck.

Usually under a heatsink, usually the biggest IC.

[neilc6]

Re: Vizio LED Driver

The model P502UI-B1 is in the eeprom replacement video for M43-C1 on Shopjimmy with no backlight which I repaired by replacing the main board after a new eeprom didn't fix it. Thread linked in post #3. Probably had the same issues.