Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

[Ianhw77k]

This TV was fine until the other day, we went to turn it on and nothing happened. I eventually found out we had sound but no picture, then did the flashlight test and diagnosed a backlight issue.
I've tested the main power board voltages to the LEDs, the black wire is giving 11.3v and the red wire is giving 116.6v after first starting at around 190v and settling down to the 116.6v.

Is it time for me to start dismantling the set further and test individual LEDs or should I be doing further testing?

Go easy on the terminology please, I'm a mechanical engineer so you'll need to explain things to me like you would to a child.

Thanks in advance for any help.

Ian.

[Ianhw77k]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Upon closer inspection I've just counted 45 LEDs so maybe 116.6v isn't right?

[sordids999]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Posting pictures of the back of your tv showing the boards with clear pictures may help you more with fixing your problem

but it does sound like a backlight issue

[Ianhw77k]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

I've found a couple of suspect LEDs on two of the strips. I will hopefully try the bridging method of repairing them (if I can find suitable replacements on ebay) and I guess we'll see where I go from there.

[ReeceyBurger123]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Well if you did some research you would know that 190v collapsing to 120v means the driver started but shut off meaning failed Led. Watch my video:

https://m.youtube.com/watch?v=RxwdC7V5Ue0

[Ianhw77k]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Yes, I've watched that video twice now, so I'm on the right track.
I've removed 3 LEDs, I just need to find suitable replacements but I'm finding the numbers a bit confusing. If I can figure out how to upload pics from mobile, I'll put some up.(I'll read through the relevant stickys now)

[ReeceyBurger123]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

That model uses C type Led I believe, message a bloke on here called Flocko he sells the Leds ready for stacking

[Ianhw77k]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Hoping the images are here.

[Ianhw77k]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

That model uses C type Led I believe, message a bloke on here called Flocko he sells the Leds ready for stacking

Great, I'll see if I have the message function yet and get on with that.
Thanks a lot.

[flocko]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Hi check out my eBay listing 252574390471 you will find what you need there (Vestal type D in the listing ) have also replied to your PM

[Ianhw77k]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Just ordered them, thanks for the quick reply.
I also ordered some of that silicone heat glue stuff, I've got some old bathroom sealant lying around in the workshop but thought I'd better do this semi properly.

Fingers crossed I can get this all back together without breaking anything and it'll work. I'll let you all know either way. Thanks for the help.

Ian.

[ReeceyBurger123]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Awesome work keep us updated.

[Ianhw77k]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

I fitted the LEDs, tested them and their connections and all seemed fine. I've partially put the TV back together, plugged it in and it still doesn't work.
One thing is different, when it first turns on, the backlight comes on for a split second but doesn't stay on. The LCD display is still working with the flashlight test.

Any ideas where I go from here?

[Andrew F. Ali]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Are you sure you connected those LEDs in the correct polarity direction?...

[ReeceyBurger123]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Are you sure you connected those LEDs in the correct polarity direction?...

+1 or didnt short out the contacts ?

[Ianhw77k]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Absolutely, checked, double checked and checked again.
Will the backlight flash if there's any connected wrong or any more that have blown? I never got a flash off it before, which leads me to think I'm heading in the right direction.

[flocko]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

sound like you still have an LED out, or a problem with the string driver on the back of the power board. you can run the backlights without the LCD fitted just leave the T.con ribbons unplugged. you can also test each strip of nine LEDs with 3X 9v batteries in series giving 27v

[Andrew F. Ali]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Well it may flash on for a brief moment then shut down if something is shorting somewhere on the connections you made or the new strips shorting the old connections....check...insulate...double check polarity connections

[Ianhw77k]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

OK, I've stripped it again and one of the replacement LEDs is out. It was fine when I got it as I tested them all. I'll try removing it and testing it again, see if my connections have gone wrong.
Looks like the kids won't be getting their film night tonight.

[Ianhw77k]

Re: Toshiba LCD TV model 40L3455DB backlight issue. (Vestel 17IPS20 power board)

Turns out that LED was fine, my soldering must have been at fault. I soldered it back in, put it back together and still getting the same problem. Just in the process of stripping it again to test the LEDs.