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

[al1415]

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

Will have to get back to you on Voltages, was taking heat sink off of main to check chips under it and got side tracked and now have to go off. real life calls..

[triplefour]

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

"real life" always gets in the way of fixing these tvs!
but what are we saying?
the real life i feel is when im fixing a tv,
the fake life is everything else in the way

[triplefour]

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

budwich did you come to the conclusion that its not using EN because looking at the traces, EN goes to nowhere, and SS also goes to nowhere? and in the datasheet it talks about using the EN and SS to do a soft start which is like... an advanced feature which could be used or not depending on application?

my question is though, if they are really going to nowhere, why are there even resistors on the way from EN to where it ends, and why is there a capacitor there on the way from SS?

[al1415]

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

CN805
Stand by
1-0 ground
2-0
3-0
4-0
5-0
6-0
7-0
8-0
9-12.2
10-NC
CN805 back lights on
1-0 ground
2-1.5
3-3.2
4-0
5-0
6-0
7-4.9
8-4.2
9-12.2
10-NC

[triplefour]

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

after reading the datasheet over and over, it seems to me like the EN pin is used even if softstart is not being used. the EN pin must be high to restart the IC in case of shutdown due to some error conditons.
in Valley Current-Limit Protection
and Output Voltage Under-Voltage Protection they mention the EN pin

[triplefour]

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

thank you al1415 i will recheck my voltages now against what you have there and hopefully i will notice something that gets me closer to figuring this beast out

[budwich]

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

I was just browsing thru the pdf and reading that either operation is possibly and since there are no components in this particular board for the "enabling", it would suggest that it isn't used.... of course, no knowing the tv history doesn't give much extra information.

IF truly the enable isn't connected to any where (do a meter check at the one "test point" and sweep thru the connector to see if any connections are found there... it would appear not from my sight).

Further, about your comment on the resistor / capacitor being "there"... I only see the labels but no components (r8207 and c8066)... if I am looking at the right portion which I think is correct based on the IC pin out numbering.

[al1415]

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

Second set of Voltages is with back lights on and off, which tells me when they turn off, TV not turning off just back lights are. Hmmm food for thought...

[budwich]

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

so if you disconnect the tcon to panel cables (power off), what happens with the backlights ...
do they come on at all, stay on?

[triplefour]

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

budwich you are correct that for the EN pin, a resistor and a capacitor are labeled but missing. but there is a 0 resistor in the path that is there. what is the meaning of a 0 resistor anyway?

and for the SS pin there is a capacitor present: c8067 which looks like goes to nowhere after that

and disconnecting one at a time, the tcon to panel cables, did not change anything. ive never seen backlight on this tv. voltage to the LED string connectors on the driver board have always been 0

[al1415]

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

they come on and then back off, board totally out of tv.

[budwich]

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

On some sets, you might not be able to run with the tcon out / not connected... just my read / limited experience.

[budm]

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

Here is the pictures of that resistor that is connected to the EN pin
What you can do is to leave the black probe on gnd, red probe on EN pin.
Then turn the TV on to see if that EN bale even goes up for second or not. If it did go high and then drops down then that means some kind of protection circuit has kick. The LED drive needs to fire up first to find out if there is any problem in that section or not if there is then the EN would go low to stop the buck converter to run that would be my logic. Something has to try to start first and then the detection kick in. But if the EN never go high the that will be some other circuit, I expect the EN pin is being used to get the BL-ON signal from the main board to start running the 4 buck converter circuits.
But at this point you are saying the TV is stuck in loop? Was it doing that before?

[triplefour]

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

thanks al1415 for the voltage readings. so i am missing the 4.2v on pin 8... only getting 0.03v
and i am also missing the 1.5v on pin 2, there i get 0.

CN805
1-0
2-0
3-3.2
4-0
5-0
6-0
7-4.87
8-0.03
9-12.0
10-NC

[al1415]

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

Did the cable thing, first unplugged cable going to main board no change, than 1 ribbon cable at a time for panel no change. Not T con issue. I know lights come up bright and then dim sooo what controls the dimming??? Issue maybe on that line if it was known.

[al1415]

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

Ya TV was in this loop ever since brought into my shop. Thought it was eeprom but wasn't it. Now at a loss. triple4 good to here now you need to track them down.

[triplefour]

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

budm i think it was always rebooting but i just didnt notice the light going off and on because it only happens after a little over a minute each time...i was probably so busy looking at voltages and the ones in the section of the driver board i was focused on werent dropping out so that i would notice. still though even i wonder how i didnt notice it earlier. maybe im wrong and it developed this new problem as well? either way im on the hunt to fix it!

oh and the enable pin reads .02 in standby .03 when turned on, and never spikes during plugging in or turning on

super nice of vizio not to label the pins of connectors on the mainboard

[triplefour]

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

so pin 8 which should read 4.2 is the grey wire and im getting .03 and on the mb side it appears to go to a tiny ceramic capacitor with .03v on one side and 0v on the other and then its real hard to tell where it goes after that. gonna have to light it up

pin 2 which should read 1.5 and im getting 0, goes to the row of pins on the mb connector that you cant tell where it goes at all (thanks for this kind of connector!)

gotta dig deeper.

edit: totally stumped now. even with the light behind the board, its too thick and doesnt let me see any of the traces. i have no idea where pin 2 goes, or pin 8

seems like once u get to mainboard problems it gets a lot smaller, a lot more components, and a lot harder to tell wtf is going on
maybe gonna have to take a chance on the mainboard. will shopjimmy let me return it if it turns out to be something else?

[budm]

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

So AL'sTV at least the backlights did come on per post #55, it comes up bright and then dims down, but your backlights did not even come on at all, that is why we need to know if the EN even tries to go high for second or not.

[budm]

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

BTW, can we see the whole backside of the TV showing how all the boards are connected together?