Toshiba 55HT1U LCD No backlight in section. Has sound and image.

[Innovator]

Hello,

I was using the television and all of a sudden the center of the picture went dim (vertically, top to bottom, about 1/3 of the display) and then then all of the back-lighting turned off, sound continued to work.

I tried restarting and you could see the back-lights try to start up and it was evident that the center 1/3rd of the back-lights was not firing up. I waited about an hour and tried starting again, this time it worked and I used it for hours. I used it on two other days after this with no issue.

Yesterday the issue came back, same center 1/3rd back-lighting wont fire up. It seems there is logic to just cut power to all the back-lighting if a section is not working. There is still sound and I confirmed there is picture by illuminating the back of the panel.

I researched and discovered that a common failure with this model is a ribbon cable connecting inverter boards. They are not adequate for the current and burn up. I took the back panel off and found everything to be in pristine condition. I re-seated several connectors and still the center 1/3rd of the back-lighting wont fire up. I want to clarify that it appears to me the start sequence is for the television to start the back-lights and check if they are working. It attempts to start them twice. I can clearly see the lighting on the left and right of the display is working properly but center is not. However this model does not seem to allow use if all back-lights are not operational. At one point last night all 3 sections of the back-light did fire, on the second start attempt. However shortly (minutes) after the center section went out and all back-lighting ceased.

I would also add that this is the first and only issue I have had with this unit. It is from 2010-11.

Could someone also explain for me how only the center (vertical) portion of the screen can go dim? As far as I can see, the CCFLs run horizontally. I would expect horizontal sections to be dim. I am puzzled by this.

Thanks.

[Innovator]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

I suppose the case could also be such that this is not a backlight issue if only a section is dim? I don't have a whole lot of display repair experience, I have much to learn.

Due to the tv immediately shutting down after quick start attempts it would be very difficult for me to capture an image, however the following picture represents the type of dimming I experienced with the exception being in my case, that this occurs in the center 1/3rd of the display:

[dick_barton]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Backlight problem in these thread:-

https://www.badcaps.net/forum/showthread.php?t=31531

https://www.badcaps.net/forum/showthread.php?t=37984

http://electronics.forumsee.com/a/m/...er-boards.html

[Innovator]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Hi Dick,

Yes, I found that thread in my research and watched the youtube video as was posted. Another poster in that thread (Louis) describes what is happening when I try to start. However upon examining the master/slave boards I find the appearance of everything to be pristine. I even reseated the 14 pin connectors that seem to be the weak point, as mentioned in my first post.

[dick_barton]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Have you checked for 24V at the fuse on both Slave & Master boards?

[budm]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Can you post the pictures whole screen shot?

[Innovator]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Bud,

At this point the tv stops trying to start the back lights after two very quick attempts at startup. The first time this problem occurred I was fortunate (relatively speaking) to have been watching it with a show playing, the center of the picture went dim but was still sharp and could see it, probably from diffusion from the left and right sections which were at full power. A few restarts after that were unsuccessful, hour after that it started up and worked perfectly up until yesterday where I had failure on first attempt.

[dick_barton]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

It appears that the backlights inverters are made up of 4 boards. 2 boards on either side of the screen.
I can't see how failure of any of these boards could result in just illuminating the centre of the screen?
Or have I missed something?

Edit:
Ignore, I missread the original post #1
It's the centre of the screen going dim.

[Innovator]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Yes, I am puzzled by this, especially since the bulbs seem to be arrayed in a horizontal arrangement. Tonight I will record an attempted startup and capture the pertinent frames.

[budm]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

It appears that the backlights inverters are made up of 4 boards. 2 boards on either side of the screen.
I can't see how failure of any of these boards could result in just illuminating the centre of the screen?
Or have I missed something?

Edit:
Ignore, I missread the original post #1
It's the centre of the screen going dim.

That is why I asked to see the pictures of the whole screen, if one inverter is not working, the half of the screen will be lit up but not in section like that as shown on the screen.

[Innovator]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Ok, well I got home today, set up the camera, started recording, turned it on and it started up first try, no problems! I played around for about 10 minutes, started a movie and kept recording. Nothing, worked perfectly. I then turned it off, started it back up and now I am getting the failure again.

I am not sure how to go about trouble shooting such an inconsistent issue.

[ReeceyBurger123]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Sure them commonly failing connector blocks are fine ? Have you continuity tested them ?

[Innovator]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Sure them commonly failing connector blocks are fine ? Have you continuity tested them ?

Yes I just checked all pins (at the board terminals) for both connector cables, everything checks out.

Additionally, I unplugged all 9 of the bulb terminals and then plugged them in one at a time (master and slave pair) and attempted to power up each time. Each set responds the same, illuminates a band from the left and right side of the screen leaving center dark/dim.

[Innovator]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Ok, I did more troubleshooting unplugging the lamps and I found that if I leave the top 2 sets of terminals on the master and slave boards unplugged the tv will attempt to boot and this gets rid of the center dimming, although now there is a horizontal section across the top that is now obviously dim. My gut feeling is that the problem has to do with the circuit for the top sets of lamps.

I also do not understand how the master slave setup works. I can plug in a master without the slave, vice versa and whatever side that is plugged in, I will get illumination from that side. I thought the M/S needed to be plugged in as pairs. Do the lamps span from one side to the other or are they 'U' shaped?

[budm]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

It is the push-pull drive circuit due to the long length of the lamps. I am still waiting to see the screen shot of the whole screen.
When you have only one inverter on one at a time, half of the screen will only light up. I cannot see how you can have all the lamp not lit up in just that section of the screen to produce that dark vertical band.

[hmendez86]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Try doing what BUD ask you.....this is no lamp fail...cfl lamps can't work just half way....if a lamp fails tv would ether not turn on or in some cases will flash and turn off while u can see picture with pointing with a flash light at screen to see picture......in this case am sure it's a panel problem tab bonding..

[budm]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

BTW, he can also disconnect the ribbon cable between the main board and the T-CON and he should see even lights on the screen.

[dick_barton]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

According to previous threads on this set, Toshiba issued a recal because of inverter board problems.
Does anyone know what Toshiba's repair comprised of.
Also, to see some of the damage due to overheating on some of the interconnecting cables leaves me wondering why not all the sets were recalled.

[Innovator]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

Ok, I need to do this in pitch black room because the only light is from the two brief flashes when it attempts to start and it is just a "black" picture. So tonight I will do this.

On another note, I need opinions. I found another 55HT1U for $100. The owner says the picture started to fail in the upper left corner and then went black and has not restarted. They only spoke to a Toshiba tech on the phone and then threw in the towel. Said something like it "needs a new LED panel". Well its not an LED, only spoke to a tech on the phone... the individual does not seem particularly savvy so the failure likely has not been investigated closely. My research points to most problems being these jumper cables frying up. Do you think this would be a good purchase for spare parts or maybe I get lucky and can get it running with new jumpers lol?

[Innovator]

Re: Toshiba 55HT1U LCD No backlight in section. Has sound and image.

I took a video. It is terrible quality, I tried 3 different cameras, different lighting and it is still very difficult to see what I am trying to explain. Photo is impossible due to how quick the two start attempts are. Here is it is for what its worth:

https://www.youtube.com/watch?v=Zlt3...ature=youtu.be