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**CapLeaker** · 12-10-2019, 11:57 AM

Re: Help with Vizio P702ui-P3 Black Screen

We need high resolution, straight shot pictures of your boards front and back.

**Russ-DS** · 12-10-2019, 02:01 PM

Re: Help with Vizio P702ui-P3 Black Screen

CapLeaker, thanks for the reply. I only have the front of the main board and part of the power board. I'll have to get the others tonight or tomorrow.

I have looked closely at the front and back of the power board and the front of the main board and don't see any blown caps or other physical damage to components (I had been expecting to see something).

FYI, the TV has been working fine for 5 years. My son was watching it last week when he said the left half went black and the right half went static/pink. He turned it off and it would not come back on.

Russ

Attached Files

**CapLeaker** · 12-10-2019, 06:41 PM

Re: Help with Vizio P702ui-P3 Black Screen

I think pin 15 on the main board is for the tcon on off. Is this this pin shorted to ground maybe? I did follow the trace trough a couple of resistors and a capacitor, then I am loosing it at a through hole. Poke around there, maybe disable the tcon enable pin by unhooking it and force the tcon enable on with either PSon or with the 1k resistor as you did. Just make sure you don’t back feed power to the main board. Turn the TV on and see what gives...

I also think you TV model ends in B3 not P3.

**Russ-DS** · 12-11-2019, 12:04 AM

Re: Help with Vizio P702ui-P3 Black Screen

Yes, pin 15 on the main board connector is TCON ON. With everything disconnected I measure 10K to gnd. I think that's probably the first of the resistors you found.

I'm not sure the best way to power it (TCON ON) with everything else on without cutting the wire. I'll try to see if I can pull it out of the connector. If I can figure this out should I expect the panel to come on?

I've attached the front and back pictures of the 4 boards.

Thanks again for all the help.

Russ

Attached Files

**budwich** · 12-11-2019, 08:56 AM

Re: Help with Vizio P702ui-P3 Black Screen

you should probably do the "disconnect of the tcon to panel cable test" to see what the results are.

**Russ-DS** · 12-11-2019, 09:46 AM

Re: Help with Vizio P702ui-b3 Black Screen

Is "disconnect of the tcon to panel cable test" the test I described above (try to disconnect the TCON ON from the main board and power it through resistor), or something different? If something different could you please share a description or a link?

Thanks,

Russ

**Russ-DS** · 12-11-2019, 09:53 AM

Re: Help with Vizio P702ui-b3 Black Screen

CapLeaker, yes, sorry, you're correct about the model number. Seems I can't edit the subject of the original post though.

**CapLeaker** · 12-12-2019, 04:51 PM

Re: Help with Vizio P702ui-b3 Black Screen

Originally posted by Russ-DS View Post

Is "disconnect of the tcon to panel cable test" the test I described above (try to disconnect the TCON ON from the main board and power it through resistor), or something different? If something different could you please share a description or a link?

Thanks,

Russ

no. Same thing, different words.

**Russ-DS** · 12-12-2019, 10:08 PM

Re: Help with Vizio P702ui-P3 Black Screen

So, disconnecting TCON ON from the main board and powering it externally did cause 12V on the TCON 12V pins on both connectors, but did not cause anything else to work. This makes me think the supply board is ok.

Separately, before I did that experiment, after putting back all the boards and reconnecting them after having been powered off for a couple of days, when I first turned the power on the backlight and I believe also the LCD did turn on. It only lasted for about 30 seconds, then turned back off. I was not ever able to get this to repeat.

Still leaning towards the main board, but please let me know what you think, as those are not cheap and seem to be hard to find.

Russ

**budwich** · 12-13-2019, 08:44 AM

Re: Help with Vizio P702ui-b3 Black Screen

Originally posted by Russ-DS View Post

Is "disconnect of the tcon to panel cable test" the test I described above (try to disconnect the TCON ON from the main board and power it through resistor), or something different? If something different could you please share a description or a link?

Thanks,

Russ

as indicated, disconnect the cables going from the tcon to the panel... this has nothing to do with cabling going from the main board to the tcon. this test is used to see if there is a panel issue and possibly other failures. Do the test by removing one cable at time and powering up to see what happens. Go from there.

**Russ-DS** · 12-13-2019, 09:47 AM

Re: Help with Vizio P702ui-P3 Black Screen

Thanks budwich, I'll try that. I believe there are 4 cables. Please let me know what I should expect to see in the case of a good or bad panel.

**Russ-DS** · 12-13-2019, 04:51 PM

Re: Help with Vizio P702ui-P3 Black Screen

I disconnected each of the 4 ribbon cables one at a time powering on in between each, but did not see anything on the screen in any case. Not sure what I would have expected though with no TCON 12V power due to TCON ON low, and with no backlight.

Before doing this I did power on again after having been off for a day, and did get the backlight on for 30 seconds or so again, with just a gray screen, but could again not get that to repeat.

**budwich** · 12-14-2019, 05:38 PM

Re: Help with Vizio P702ui-P3 Black Screen

:-( I was hoping perhaps that you would get some screen flash... thinking that perhaps the "loss of 12v" was so quick that you can't "normally" see it.

back to your "forcing the tcon on" method. If you do that method and have one of the tcon to panel cables disconnect (either end side), do you get any reaction on the screen as opposed to totally dark screen?

Also, what voltages have you checked at the main board? Never mind I see that you have indicated most.... but maybe the question is... where are you checking the voltages at both the power board AND the main board?

I don't see a good picture of how all the boards are connected.

**Russ-DS** · 12-16-2019, 09:31 AM

Re: Help with Vizio P702ui-P3 Black Screen

I've had no luck getting screen flash with Tcon cables disconnected, however I continue to be able to get it to power on with backlight for <1 minute after being off for an extended period of time. It then shuts off TCON ON/TCON 12v and the backlight.

When on, the left half of the screen seems to be working fine, while the right half is full static (see attached (very poor) photo).

Attached Files

**budwich** · 12-16-2019, 02:12 PM

Re: Help with Vizio P702ui-P3 Black Screen

I guess the question is are you trying to locate AND fix a problem at the board level or are you just going to replace a board.

I would say your issue is either at the main or cabling going from the main to the tcon. have you carefully checked the lvds cabling between the two boards looking for bad pins / tracks? As suggested, have you checked some of the voltages at the main.... yes there is no labeling but there is some at the power board... "transcribe" / follow those to the main board to see that they are there and in "good standing". Further, there are "known voltages" on things like hdmi connectors and usb connectors... ensure those voltages are there... they might give you a clue to missing voltages some where.... if you are lucky.

One other point... have you looked under the "lid".... the "can" for emi and heat sinking? You might spot something there.

**Russ-DS** · 12-16-2019, 04:59 PM

Re: Help with Vizio P702ui-P3 Black Screen

Good question, ideally I would like to repair the issue rather than replace the board, but am starting to suspect that may not be possible or as easy as I'd hoped. I'll go follow some of those voltages and check and re-seat the cables again and see if I an find anything.

Thanks again for the help.

**budwich** · 12-16-2019, 05:33 PM

Re: Help with Vizio P702ui-P3 Black Screen

hopefully you find something.... note there is more than one 12v "run" to the main... ensure that those are indeed getting there and if possible track them to some of the areas "inside" the main... potentially towards some of the display chips.

**Russ-DS** · 12-17-2019, 08:00 PM

Re: Help with Vizio P702ui-P3 Black Screen

I can't seem to find any issues after some additional probing around. No visible issues under the heat sink either. The set continues to be able to be powered on for < 1 minute after having been off for a while before it shuts off the panel, with the left side working normally. I've attached a better picture of that.

I'm thinking I should just pull the trigger on a new main board, as I'm running out of ideas.

Attached Files

**budwich** · 12-18-2019, 07:35 AM

Re: Help with Vizio P702ui-P3 Black Screen

not sure if you tried this previously but with the "can off", you can try doing some "light heating" (hair dyer) at some directed points to see if you get any changes.

The picture that you show is almost like a "cable disconnected" picture in that when you disconnect one of the four cables (furtherest to the side), the display for that side goes white and "normally" a clean white, uniform and without lines or display. Since you have all cables connected and get this, that would indicate that the display "drive" circuits for that side have issue and the display is not "clean" almost like a "noisy" bad cable similar to an hdmi cable type issue... hence the possibility that the cabling from the main to the tcon has a problem. Sometimes the "folds" can be an issue. You could carefully look at that but my bet is still more towards the driver of the cables than themselves. One other point, do you get any sound when you get the this partial picture (ie. feeding in a source).?

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Help with Vizio P702ui-P3 Black Screen

Help with Vizio P702ui-P3 Black Screen

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