Toshiba 40D1333B No Backlight

[london-freddie]

Hi guys just spent all evening playing with this Toshiba 40D1333B with no backlight
When powering up the tv the backlights flash on for split second then off, ah ha another failed led or so I thought
Tested voltages at led connector got 24 volts so then stripped the screen panel LTA400HM23 to find the dead led/s. However all working using my backlight tester, checked full circuit and every connection all seems good.
This screen panel does have an inverter in the panel, crap idea if you ask me.
Built the screen back up and now asking for help please, Power board maybe or maybe the inverter
Testing PL306 on the power board supplying the leds I have pins 1 to 5 showing 24.6 V, pins 6,7,8,9,10 showing 0V, pin 11 showing 1.3V, and pin 12 showing 3.2V.
Does that sound ok
I am not at home tomorrow so will be sunday before I can look at this tv again
Any help please
Will get my pics on asap

[london-freddie]

Re: Toshiba 40D1333B No Backlight

Pictures as promised
Picture of the inverter is not my inverter as I had reassembled my screen but am sure this is the same as mine
Only other thing that I have noticed is when the set is powered on there is a buzzing from the power board, can not pinpoint where it is coming from yet

[Diah]

Re: Toshiba 40D1333B No Backlight

how about the sound... do you still have it ?
you may read this threat too https://www.badcaps.net/forum/showthread.php?t=45871

[london-freddie]

Re: Toshiba 40D1333B No Backlight

not had it connected to a source, and speakers removed with back cover so not sure if there is sound
Doing the torch test I can see the menu showing on the dark /black screen

[london-freddie]

Re: Toshiba 40D1333B No Backlight

I have just been reading that post by Dang seems exactly the same problem as I have got with this tv
when I had the screen apart I checked every strip separately and all leds lit fine
I also checked the whole backlight circuit from the two test points on the inverter again every led on every strip lit at the same time with no problems showing
fuse F1 on inverter board tested good

[Diah]

Re: Toshiba 40D1333B No Backlight

if you plug out the socket from power board to LED driver the 24 volts and plug it again little fast the BL will be on ?? no problem you can do this also with out LCD in place if you take it out
led tester fail to to test the ziner diode of the LED for forward currents, this ziner if get shorted led failed by circuit. best way to test DM in diode mode test each with tow way of changing the probe + and -

[london-freddie]

Re: Toshiba 40D1333B No Backlight

Hi Diah just tried removing and plugging back in , still no backlight

[london-freddie]

Re: Toshiba 40D1333B No Backlight

Hi Diah where is the Zener that you are referring to, is it on the power board or on the inverter board

[Diah]

Re: Toshiba 40D1333B No Backlight

Hi Diah where is the Zener that you are referring to, is it on the power board or on the inverter board

each LED had Zener bulid in to to control the currents forward. this could be open or shorted.. so you can find LEDs lighting up but its Zener open or its Ohm going down near to be shorted.. so currents will be changed , the led driver detect this change and turn them all out. also take your time to check them one by one with DM diode mode

[london-freddie]

Re: Toshiba 40D1333B No Backlight

OK thanks for that, am at work tomorrow but all being well I will strip the panel again tomorrow evening and recheck

[zomi]

Re: Toshiba 40D1333B No Backlight

Hard wire all the connections
just to rule that out.

[london-freddie]

Re: Toshiba 40D1333B No Backlight

OK Update on this tv
Stripped panel again today to get to and check led's
Checked with backlight tester and all led's lit
Then removed all led strips and slightly bent all the plastic connectors on the ends of the strips to ensure a firm connection between strips
Re assembled panel and led's all lit under the tv's power
Tv now back together and seems to be working fine
Conclusion there must have been a poor connection or connections between led strips or inverter to strip
I am happy now but boy what a crap tv this is

[johnny250]

Re: Toshiba 40D1333B No Backlight

Hi Freddie, is it still working OK?..... I have the same set with the same problem.....any tips on the dismantling procedure?

[johnny250]

Re: Toshiba 40D1333B No Backlight

this looks like it could be my problem too..... https://youtu.be/AeAGI0yNgEM?t=203

[johnny250]

Re: Toshiba 40D1333B No Backlight

Contacts are OK on mine, It has a Samsung LTA400HM23 panel, with at least 5 LED's faulty
it has LED's in strips of 4 and 5 LEDs. (10 strips, 43 LED's)
Some numbers on the strips : SVS400A79 4 LED and 5 LED A,B,C and D types

anyone have a source for replacements?.THANKS!

[diif]

Re: Toshiba 40D1333B No Backlight

Contacts are OK on mine, It has a Samsung LTA400HM23 panel, with at least 5 LED's faulty
it has LED's in strips of 4 and 5 LEDs. (10 strips, 43 LED's)
Some numbers on the strips : SVS400A79 4 LED and 5 LED A,B,C and D types

anyone have a source for replacements?.THANKS!

Ebay or Aliexpress, for either strips or individual LEDs.

[hicsvntdracones]

Re: Toshiba 40D1333B No Backlight

I am having a similar issue with a Toshiba 43L612U. When I plug it in the logo flashes up for a second then the backlight goes off, along with the display I think, can't see anything on with a flashlight to the screen. The more I use it, the faster it shuts off until I get just a quick flash of white. If I let it sit or drain all the power, I'll get the logo again for a second at max. All the other posts & videos i've watched end up with an LED issue, though my multimeter isn't giving any similar results. When it first powers on, the backlights jump to about 70 volts (it is very fast til they shut off) then they drop down to 45 volts and stay stable, when the BL shuts off. All 3 led power connections have the same pull and the voltage coming back in is also the same and very small, so it doesn't look like a bad led or short. all the pins have the correct voltage from PSU to COntrol board to T-con, except DIM & BLON, which sit only at 3.5 volts constantly, though when I turn on the TV, it seems like DIM goes to 1.5V then jumps to 3.5 V as soon as the leds kick off, but it is quick and could just be an artifcact of my DMM.Not sure if this TV uses 1.5v to 3.5 or if they all use 3.5v to 5v for those pins. The Power LED blinks red when plugged in, then goes solid red, when i hit the power button, it just goes off.

I keep thinking it is a capacitor, since the more drained the voltage is, the longer the backlight stays on initially, but could be something completely different, I am simply "dangerous" in terms of experience and more or less stop at Arduino projects, though have been known to Mr. Magoo my way through some PCB repairs.

I did try jumping DIM to BLON as has been suggested in the past, with no luck. I am considering forcing the backlight on to verify if I am getting an image also, but want to verify if I need to jump BLON to PWON with 1k jumper or BLON to a nearby 5v on the board, or something different.

Anyone see this before? Sorry to jump in off this post, but can't find my old login so new acct, and similar thread.

[nomoresonys]

Re: Toshiba 40D1333B No Backlight

Don't see the pinout legend but it's usually jumper from pwon to 5 v stndby plus blon to 5 v stndby both, expected voltages should be there and backlights should come on and stay on as long as jumpered. MAKE SURE cable from powerboard to mainboard is UNPLUGGED for this test.

[nomoresonys]

Re: Toshiba 40D1333B No Backlight

Try unhook cable from powerboard to mainboard, plug power cord in, turn on see if backlights come on and stay on, actually this is the test you do before the one above.