Toshiba 50" 50L3400U blinking backlight

[doh13]

Re: Toshiba 50" 50L3400U blinking backlight

Since you disconnected the Dimming control line then the on screen backlights level will no longer have any effect.
Do you have any kind of resistors in stock, it may be easier than trying to explain how how to get the hook up the pot.

I am able to dim the screen so i obviously do not have the dim disabled not to mention the screen just started flashing again when i increased the backlight .
I do have some resistors but I haven't got access to them today. I am not a pro i am still learning so be gentle with me .

[doh13]

Re: Toshiba 50" 50L3400U blinking backlight

BTW, what DCV do you have on the DIM pin for the LED DRIVER board?

Not sure about the DCV i left my voltage meter at home and i obviously dont know where the dim pin is yet lol right now i havent got the tv apart as i have to get ready for work but i do want to try what you suggest to lower the voltage going to the led strips. if i can accomplish that then I will likely replace the strips as i know they will last longer. if i need resistors which ones should i have ( i may need to order them)

[budm]

Re: Toshiba 50" 50L3400U blinking backlight

If you can run the LED at lower level with all the cables in place then I would just do that and use it until the LEDs are dead.

[doh13]

Re: Toshiba 50" 50L3400U blinking backlight

It runs at a low backlight setting so i guess maybe i will just do that and then worry about adding resistors at a later date or just toss it in the garbage lol. thanks for the help i appreciate it.

[budm]

Re: Toshiba 50" 50L3400U blinking backlight

The added resistor is for if you disconnected the DIM control line due to bad dim control signal but right now you do not have bad dim control signal because the backlights are on and dimmable.

[ngth82]

Re: Toshiba 50" 50L3400U blinking backlight

OP here.

I did not take the panel apart. It still works, but now the brightness is set to 50-55 to stop the blinking. I can't complain since it was a freebie. Like I wrote in one of my earlier posts, I'll take it apart when the blinking becomes a chronic problem. It works right now.

I would highly advise again running the LEDs without at least a small few ohm resistor in series. This will act like a fuse for you if there is a problem (e.g.short) from one of the wires to the tv chassis. I don't have the TV schematics in front of me right now, but I'll take a look when I get home from work.

The TV is plenty bright for my application -- even with the panel dimmed down to 35-40. Why cut the wire at all?

Glad to see others are contributing to the post too!


Cheers,
Thomas

[ngth82]

Re: Toshiba 50" 50L3400U blinking backlight

OP here.

I did not take the panel apart. It still works, but now the brightness is set to 50-55 to stop the blinking. I can't complain since it was a freebie. Like I wrote in one of my earlier posts, I'll take it apart when the blinking becomes a chronic problem. It works right now.

I would highly advise again running the LEDs without at least a small few ohm resistor in series. This will act like a fuse for you if there is a problem (e.g.short) from one of the wires to the tv chassis. I don't have the TV schematics in front of me right now, but I'll take a look when I get home from work.

The TV is plenty bright for my application -- even with the panel dimmed down to 35-40. Why cut the wire at all?

Glad to see others are contributing to the post too!


Cheers,
Thomas

D'oh! I'm looking through my service notes on the TV -- i couldn't find a service manual with schematics of each panel for this unit, but this is the next best thing:

https://philips.encompass.com/shop/m...m/50L3400U.pdf

[doh13]

Re: Toshiba 50" 50L3400U blinking backlight

I was under the impression that removing pin 15 or disabling the dim would stop the blinking by not allowing the dim control to give the reading that there was no signal from the burnt led bulbs I think this tv will work well with the dim set in the same range as you are using so I will try it and see rather than take everything apart. If I ever do change the bulbs I will look into it further. Thanks for the link

[budm]

Re: Toshiba 50" 50L3400U blinking backlight

Dim is the control signal generated by the main board, it is not an error signal to tell the main board if the LED or the LED driver are good or bad, the main board get the error signal from the LED driver if the error signal is implemented, most cheap TV does not use error signal to tell the main board to shutdown the TV..
Most LED driver circuit will shutdown the driver when it detect no current flow through the LED string if it goes open circuit, it will also shutdown the circuit if too much current is flowing through the circuit if there is shorts.

[Papadaddy]

Re: Toshiba 50" 50L3400U blinking backlight

I wanted to confirm some of the theories on this thread. I have had a 2-3 year old Toshiba 50L1400U that has had the same blinking problem, that got so bad the TV became permanently black. I replaced the TV completely and left it off for a month or two, decided to see if it worked for funsies, and it does. 30 minutes later the blinking returned and i found this forum, followed the easy steps (dimming the lights and turning off dynight), it's been an hour and no issues yet.

If replacing the LED strips is a garaunteed fix for when it happens again on low settings, please let us know. Thanks guys, awesome work!
-first post ever

[ngth82]

Re: Toshiba 50" 50L3400U blinking backlight

I wanted to confirm some of the theories on this thread. I have had a 2-3 year old Toshiba 50L1400U that has had the same blinking problem, that got so bad the TV became permanently black. I replaced the TV completely and left it off for a month or two, decided to see if it worked for funsies, and it does. 30 minutes later the blinking returned and i found this forum, followed the easy steps (dimming the lights and turning off dynight), it's been an hour and no issues yet.

If replacing the LED strips is a garaunteed fix for when it happens again on low settings, please let us know. Thanks guys, awesome work!
-first post ever

Yes, that's the working theory for the TV. I completely agree that it's at least one bad LED on my TV (the lower right hand corner is slightly darker when displaying a solid white screen). The blinking frequency increases as the screen brightness goes up (overall voltage to the LED strip goes up -- more current == more light == more likely to exhaserbate the problem). The blinking slows down, and eventually stops when the screen brightness gets dim enough.

The reasons why I have not yet dismantled the TV panel to the point of replacing the LEDs are:

1) Possible damage can occur to the display itself when you do so
2) Replacement parts for the display is not worthwhile (in my case) since the TV was free.
3) Sourcing parts for an entire strip may prove to be problematic (but worst case, one can just replace the single burnt out LED (or LEDs) with an off the shelf one of the same voltage rating).
4) It just "works" for now with the dimmed brightness. No reason to really take it apart until it completely dies.

I'll definitely post to this thread if / when i end up taking the TV apart and share my findings for future folks that run into the same issue. For now, the panel remains fully assembled.

-Thomas

[martino]

Re: Toshiba 50" 50L3400U blinking backlight

1) Possible damage can occur to the display itself when you do so
2) Replacement parts for the display is not worthwhile (in my case) since the TV was free.
3) Sourcing parts for an entire strip may prove to be problematic (but worst case, one can just replace the single burnt out LED (or LEDs) with an off the shelf one of the same voltage rating).
4) It just "works" for now with the dimmed brightness. No reason to really take it apart until it completely dies.

No sense of adventure

[ngth82]

Re: Toshiba 50" 50L3400U blinking backlight

No sense of adventure

Lol... I'm an electrical engineer during the day -- i design and debug enough internal reference designs and customer designs as-is. I don't need another project if i can avoid it

[Mike Hutchison]

Re: Toshiba 50" 50L3400U blinking backlight

IC U901 (OZ9998HDN) you can buy it here:
http://www.ebay.com/itm/222431015355?...
Seller E-Bay user name:hifiic

[ngth82]

Re: Toshiba 50" 50L3400U blinking backlight

IC U901 (OZ9998HDN) you can buy it here:
http://www.ebay.com/itm/222431015355?...
Seller E-Bay user name:hifiic

Interesting... maybe you posted to the wrong thread?

The only OZ9998 part that i can find is for a 3-way SMBus multiplexer. .... not part of the TV issue noted here.

[ngth82]

Re: Toshiba 50" 50L3400U blinking backlight

Hi Mike -
I'm just following up with you on the OZ9998HDN part recommendation.

I see that someone posted a similar video on YouTube for the same TV. I'll give it a go. It's only $5.50 total including shipping. I much rather keep this TV and use it instead of selling it for dirt cheap. It's a nice TV set!

https://www.youtube.com/watch?v=FSzF2TJh20A

-Thomas

[martino]

Re: Toshiba 50" 50L3400U blinking backlight

I can confirm that replacing that chip will solve your problem.

While you replace it,try and improve the contact area of cooling plate to the chip,its piss poor from the factory,barely any contact.I believe thats why the chip fries.

[ngth82]

Re: Toshiba 50" 50L3400U blinking backlight

Thanks Martino.

Some days i should leave electronics alone.

I decided to remove the heat spreader and unsoldered the existing part. I scraped off the existing thermal interface material and replaced the bottom side with a high quality thermal paste, and a sheet of thermal interface material on the top. I soldered it back in place and unfortunately, it looks like two of the four edge lit LED strings are now not working. Like i said... some days I should just leave things alone!

I will test the strings individually using my bench supply in the coming few days. I'm hoping the issue is just with the driver IC, and not the LED string itself.

I'll purchase the replacement IC anyway. It's only $5.50. Why not. Better than buying a new board all together.

[ngth82]

Re: Toshiba 50" 50L3400U blinking backlight

Update:
I received a replacement LED driver IC. The blinking problem is still there.

I'll be taking this TV apart and individually check each string for busted LEDs. The saga continues...

[ngth82]

Re: Toshiba 50" 50L3400U blinking backlight

The TV has been taken apart. There are 10 bad LEDs on the edge lit display.

The LED string markings are "V500H1-WE1-TLEW9" and "34-D096530". The LED string is mounted on an stainless steel panel that is about 8" wide and runs the entire vertical length of the unit.

Looks like the LED string itself is 18.70 from China on eBay.
I can get it local (state side) with the stainless panel for about $70.

This TV is a pain in the ass to take apart for sure.

I reassembled it so I can get it out of the way and reclaim my living room floor.(thankfully, the screen did NOT crack). This toshiba unit was originally on my wall for a big Chromecast picture frame setup. I now have a 42" LG smart TV there in its place. I may spring for the LED string from China.. but I can't justify spending $70 on a TV that i got for free.