Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

[Michale32086]

This past weekend, I got in a really nice D55un-E1 Vizio...

The guy who brought it in swore up and down that it worked fine, but when he brought it in to sell, I got a power light, backlights and sound, but no display...

I fiddled with it, checked if it was set for AUDIO ONLY (it wasn't).. Checked all the connections to the TCON and Main Video.. All good...

So, I bought a new Main Video board.... No luck.. Still have backlights, but no display..

Thinking TCON, I bought a new TCON.. Still no luck.. No display at all..

The "tab bond" boards attached to the display panel look immaculate.. No obvious burns or shorts.. The tab bonds themselves look in great shape.. No rips or burns or holes/cuts...

LVDS cable looks in great shape.. Everything looks brand new without a hint of corrosion or blemish...

So I am thinking either a short or fry on the tab bond boards that is not visually apparent...

Or a bad Power PCB... I can't imagine a Power board would cause this problem, but I really don't have any other possibility..

And when one removes the impossible, whatever left, however improbable must be the solution..
-Occam's Razor

Is it possible that the Power PCB could have this symptom???

Pics are attached...

[budm]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

You do have 12VDC feeding the T-CON?
What do get on the screen if you have ribbon cable between T-CON and LCD panel connected one at a time?
I would check the Voltages on the T-CON board by looking up spec sheet for IC4002 (RTxxxx) LCD Bias IC, and also Voltages and DC resistance of the caps to see if any one of them show low resistance or not, if it does then disconnect cable to the LCD panel to see if the low resistance goes away.

[Michale32086]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

What do get on the screen if you have ribbon cable between T-CON and LCD panel connected one at a time?

When I remove the left ribbon cable, there is no change.. just a backlit black screen with no display..

When I remove the right ribbon cable, the right side of the screen is backlit white and the left side is backlit black..

I'll check those voltages now..

[Michale32086]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

At the marked points, I have 12.04V

[Michale32086]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

Any tricks to locating a spec sheet for RT6914??

Google doesn't seem to be much help..

[Michale32086]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

Came across this in a YouTube video..

https://www.youtube.com/watch?v=B4scn4hyo_M

[Andrew F. Ali]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

Is this the exact T-CON Bd. you have?

[Michale32086]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

Is this the exact T-CON Bd. you have?

No... This was kinda a generic TCON Youtube video in a foreign language.. But I thought that the overall design of all TCONs are similar..

Apparently, I thought wrong.

[budwich]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

When I remove the left ribbon cable, there is no change.. just a backlit black screen with no display..

When I remove the right ribbon cable, the right side of the screen is backlit white and the left side is backlit black..

I'll check those voltages now..

the "reaction" with the white screen is the "correct one", the other one indicates a failure on the side that is disconnected. However, the failure may be such that it is pulling down the "better side" such that you were not able to get a display...OR nothing was being displayed at the time for you to see...:-) were you inputting something?

[Michale32086]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

the "reaction" with the white screen is the "correct one", the other one indicates a failure on the side that is disconnected. However, the failure may be such that it is pulling down the "better side" such that you were not able to get a display...OR nothing was being displayed at the time for you to see...:-) were you inputting something?

Yea, I had an HDMI device hooked up.. But I didn't see anything, not even a channel or volume or menu display when I pushed the appropriate buttons.

So, yer thinking the problem is on the side of the panel that still shows black at disconnect???

[budwich]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

As you saw on the other side with that side disconnected, there is some screen voltage that gets to the panel to allow the "white screen" (basically LCD crystal has been powered to transmitted clear to allow backlight thru). On the bad side, some how that same voltage is not on the panel and hence it is black. Voltage checks especially along the bottom edge board may reveal a difference between sides or an obvious component issue.

[Michale32086]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

As you saw on the other side with that side disconnected, there is some screen voltage that gets to the panel to allow the "white screen" (basically LCD crystal has been powered to transmitted clear to allow backlight thru). On the bad side, some how that same voltage is not on the panel and hence it is black. Voltage checks especially along the bottom edge board may reveal a difference between sides or an obvious component issue.

Would you have any suggestions on exactly where to check voltages??

I am getting on in my years and my hands aren't as steady as they used to be...

I know that area is very sensitive to ESD. Would hate to frak it up more, if that's even possible..

[nomoresonys]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

Sometimes if there's a fault on the driver board it will show by one or more of the little ceramic caps on the tcon will read shorted, unplugging the faulty side ribbon from tcon to panel and cap/s won't read shorted.

[budwich]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

Would you have any suggestions on exactly where to check voltages??

I am getting on in my years and my hands aren't as steady as they used to be...

I know that area is very sensitive to ESD. Would hate to frak it up more, if that's even possible..

me too... :-) I don't do a lot of "power up checks". Basically once you find a power point that is easily accessible on a board (eg. 12v say), I then try to follow things with power off and using a resistance scale following continuity / short to another area / component on the board, and continue like that perhaps powering up at that point to confirm... again finding easy points.

Further, usually on the tcon at the bottom, there are a number of labelled voltages such a Vcom, etc. See if you can get easy access to those. A number of those voltages find there way to the panel edge boards at the bottom. If they are at the tcon, then you can track / trace from there towards the edge board. As suggested, just above, again using no power on the set, use you resistance scale and measure some of those labelled voltages... if there is little or no resistance, then it is likely that the subtending circuit has an issue either loading the potentially voltage and taking out the driver of that voltage because of a short or otherwise.

[budm]

Re: Vizio D55un-E1. Excellent Cosmetic... Backlights, Sound, No Display..

Since the T-CON board does not have any marking the Voltage test points and I cannot find the spec for RT6914, so if I were you I will keep the cables between LCD panel and T-CON in place but not the LVDS cable going to the main broad; then start checking the DC resistance of all the caps to see if any one of them shows low resistance reading in both directions or not first.