Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

[triplefour]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

can we confirm which chips we're talking about here guys? bud asked for U301, but i didnt find that on the driver board so i posted what i thought he meant, (or thought he saw) at U804 ( there is a U801 and 8 can look like a 3 if its blurry enough)
which location are you referring to, AL?

if there was an IRC channel for this forum i'd be idle in it 24/7

[al1415]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

The LED driver IC's U801 through U804 he used U301 as an example on what to look for. The part numbers that i gave are to the 4 buck converters IC's at connector to main board.

[budm]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

Found this link that gave more info on chip..

I am glad you found the spec sheet. the dialog web site does not provide info until you create user name and pass word.
It is complex LED driver chip.

[al1415]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

That it is. Very complex.

[budm]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

BTW, I do have this Vizio in the validation lab that I use everyday, hopefully it does not go out yet.

[al1415]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

Not sure where to start on these. It does mention being tied to transistors but their is none only on power board. Not sure yet what the 6 legged IC's are yet unless they are being used as transistors. All resistors that are in a row on all 4 circuits are according to my meter sounding off on either side of them in diode mode they are in ground rail. And the package has a fault sense for a short or open circuit.

[al1415]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

Hope not, its a pain... Royal pain...

[al1415]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

Ut oh... got to quite over here. Budm any thoughts on these led control chips? Like where to start, what portion makes lights dimm?

[al1415]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

Like i said instead of lights dimming down, screen just go's black at the point instead of being dim for normal screen view.

[triplefour]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

i havent given up, but im working on other TV's at the same time. will definitely post updates on this one's progress if i make any.

[budm]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

Ut oh... got to quite over here. Budm any thoughts on these led control chips? Like where to start, what portion makes lights dimm?

I would monitor the X fault pin on each one of the LED Controller IC you will need to leave black probe on the chassis and red probe on each LED controller IC X fault pin then turn on the TV to see what happen when the backlights come on and the go black, then turn the TV off and move the red probe to the next IC and turn the TV on and look at the Voltage. Do the same on the rest of the LED controller.
We need to see if that is why the backlights come on and then go off due to fault detection or not.
I believe it will go low when fault is detected.

[al1415]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

Each X fault pin reads 3.1/3.2 volts weather back lights on or off. In fact when I plug TV in I get 3.2v power lite is on and when it fades and goes out than 3.2v drops to 0v. Press power button and get 3.2v.

[al1415]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

Press power button to turn TV on and get 3.2v that is.

[midnightg35x]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

I'm going to chime in here that I have the same TV with identical symptoms to triplefour. My backlights do not try to fire at all like al1415. I have tried replacing the EEPROM with no luck.

I'm interested in some other ideas also. The fact we never get the BL_ON (or EN to U801-804) really seems to point to the main board not doing something. I'm open to suggestions for what to check. I noticed on my main board at least the TCON_ON signal does not act properly either. I manually did grounded the gate of the transistor that controls this and the TCON_12V did end up turning on and going to the TCON.

[midnightg35x]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

Just a follow up to this. I took a couple thermal shots of the main board with the heat sink removed. Everything to me in this post is pointing to the main board, so I figured I would try to reflow the two main IC's. I have access to nice equipment, so I feel comfortable doing this. One certain gets warmer than the other during the attempted power on, but neither give anything definitive. I did not run them without a heatsink for more than a minute.

Thermal and normal of IC near RCA/HDMI jacks





Thermal and normal of IC closer to TCON and power cables





Any other testing suggestions are welcome

[triplefour]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

neat what do you use to take the thermal images?

[midnightg35x]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

neat what do you use to take the thermal images?

A FLIR One Gen 2 https://www.flir.com/support/products/flir-one-gen-2

It helps finding shorted components sometimes without using my finger everywhere. Unfortunately, it didn't seem to help much with this problem. Those two chips should be getting warm even when operating normally. I'd really like to have some suggestions on where else to look besides just ordering a new board.

I have an external power supply to try to turn on the LED board, but it seems I would need a couple of them for the dimming and other signals. I'm not sure what voltages I would send over just to try it.

[al1415]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

Thanks for the info midnightg35x, was fixing to do the same thing you did. We need a service manual and right now I cannot a ford to purchase one at the moment

[midnightg35x]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

I did one quick check that if I apply +5V from an external supply to the LED driver board on the gray wire, the 4 converters do show +12V at L801-L804. The LED did not light up yet though. So far I have the TCON_ON signal and BL_ON signal are not getting to their respective boards. Even more signal of a main board issue. I wish there was an easy way to figure out which chip was the problem or if it is even worth chasing down. I'd rather not buy a new main board, but that's where this is looking to me.

[al1415]

Re: Vizio P502UI-B1E has no backlight, no voltage from driver board to LED's

In the beginning on i had backlites when TV turned on, then when vizio logo go away just black screen. After plugging and unplugging and checking voltages i get only black screen and no backlites also no voltages going to T-Conn or LED driver board. On the main board their is A Synchronous Step-Down Converter location U712 Pin 2 was 1.3 volts now only .7 volts, also X201 has no voltage or the cap at connector for lvds cable to T-Conn no voltage where as before i lost backlites altogether i did have. I agree though issue is main board just what chip is the question. Could be U7612 breaking down under load maybe??