Toshiba LED TV, blank screen

[budm]

Re: Toshiba LED TV, blank screen

Tv stays on for like 2-3 hours without any resistor or modification, then it blacks out.

Last night I went in to the customer menu and lowered down the backlight setting from 100 to 30 and stayed on all night. This morning I thought I could probably bump it up to 50 but it started flashing again so I left it on 30 and is playing fine.

Would you say that my LED's are extremely bad ?

Yes, they are in real bad shape. If if it cannot work at 50% then you have to change the LEDs or live with less backlights until it dies. Also tell the customer when they get new TV to lower the backlights level down as low as possible to extend the life of the LEDs. It does not look like no matter what brands of TV you buy, they all seem to have bad LEDs problems.

[Louis82]

Re: Toshiba LED TV, blank screen

Tv stays on for like 2-3 hours without any resistor or modification, then it blacks out.

Last night I went in to the customer menu and lowered down the backlight setting from 100 to 30 and stayed on all night. This morning I thought I could probably bump it up to 50 but it started flashing again so I left it on 30 and is playing fine.

Would you say that my LED's are extremely bad ?

[budm]

Re: Toshiba LED TV, blank screen

Hi budm. My tv without making any modification (disconnecting yellow wire or adding a resistor) already measures 3.5v on pin 13 LED driver board. Is that normal? In post #82 you mention that it measure 5v full backlight power and that you add a resistor to lower it down to 3.5v.

I tried what you guys been doing here, disconnected yellow wire pin 15 and I added a 200kohm resistor and power goes down to 2.2v and the screen flashes and goes black. I added another resistor 280kohms 2.8v and same thing. Any input?

Thank you

But do the backlights stay on without any resistor, if not, then your LEDs are too far gone.

[tibimakai]

Re: Toshiba LED TV, blank screen

My TV, it was running OK for hours at a time, so yours may be in worse shape, then mine.
Bud should chip in.

[Louis82]

Re: Toshiba LED TV, blank screen

Yeah I did that. Lowered down to 2.8v and screen flashes in less than a minute.

[tibimakai]

Re: Toshiba LED TV, blank screen

Mine shows 3.5V as well, at maximum brightness. With a resistor, I have dropped it at 2.8V.

[Louis82]

Re: Toshiba LED TV, blank screen

Hi budm. My tv without making any modification (disconnecting yellow wire or adding a resistor) already measures 3.5v on pin 13 LED driver board. Is that normal? In post #82 you mention that it measure 5v full backlight power and that you add a resistor to lower it down to 3.5v.

I tried what you guys been doing here, disconnected yellow wire pin 15 and I added a 200kohm resistor and power goes down to 2.2v and the screen flashes and goes black. I added another resistor 280kohms 2.8v and same thing. Any input?

Thank you

[Agent24]

Re: Toshiba LED TV, blank screen

I run my LCD monitors at about 40% brightness. Unless you have bad eyesight I don't know why people run them at 100%.

[tibimakai]

Re: Toshiba LED TV, blank screen

Yes, it runs cooler.
That is a good idea.

[budm]

Re: Toshiba LED TV, blank screen

Did you notice that it does dim down the backlights and runs a little cooler too?
I told people that want to buy new TV to set the backlights level as low as possible to extend the life of the LEDS.

[tibimakai]

Re: Toshiba LED TV, blank screen

OK, I have added two resistors in series, total value is 231Kohm and the voltage is 2.8V.
That is, a 80% value from 3.5V.
I will leave it at that.
To me, it looks good.
Thank you everybody for the help, specially Bud.
Now, I need to move on, to the Sony Google TV.

[tibimakai]

Re: Toshiba LED TV, blank screen

He has, way to many videos. Could you please, let me know at least, which brand TV it was?

[ReeceyBurger123]

Re: Toshiba LED TV, blank screen

Ahh right I see sorry still learning and haven't read most of the thread.

[budm]

Re: Toshiba LED TV, blank screen

If it has BAD LEDs, then removing the PWM dimming control line will not make the BAD LEDs to come on and stay on, but bad LEDs are common failure for backlights LED TV.
The one I worked on has two problems, one is the PWM signal, and one of the LED strip goes out when hot (you can see the LEDs flicker) then after about an hour the circuit will shutdown when that LED strip stops working.

[ReeceyBurger123]

Re: Toshiba LED TV, blank screen

Got to youtube and search for Norcal715 he has a video of a similar set its his latest upload which shows that the tv had a bad led inside of the panel wich was causing the issue that you have described.

[budm]

Re: Toshiba LED TV, blank screen

It is the main board problem, when the TV is first turned on the PWM signal is present (>4VDC) for seconds (backlights flash on) and then it drop down to <0.5V. I never spend the time to troubleshoot the main board to locate the root cause of the problem.

[tibimakai]

Re: Toshiba LED TV, blank screen

We still don't know, what is the real fix right?

[budm]

Re: Toshiba LED TV, blank screen

No need to remove the wire from pin 15 on the LED driver board, I remove the wire at the power supply board as shown in picture #2. You already removed the PWM wire so no need to remove the pin 15 wire at the LED driver board, as you can see I leave it connected.
"This TV, you have kept it for yourself?" I gave it to my friend daughter to use in her bed room, she left it on 24/7 so far for two weeks now, I gave it to her so I can keep track to see what happen.

"It can be sold, with this repair?" You will have to tell the customer hat the backlights level cannot be adjusted any more.

[tibimakai]

Re: Toshiba LED TV, blank screen

The lead, from #15 has to be removed, when the resistor is soldered there?
This TV, you have kept it for yourself?
It can be sold, with this repair?
I would rather keep the Sony Google TV, after we repair it.


Yesterday, I have scored a Fluke 189 in very good condition from CL. Only meter, leads and a bag(not Fluke).
The only problem that I have found out after I have tried using it home, that the LEADS was showing up on all positions of the switch. At the purchase location, it was working fine(weird). I have tested the amp side when on switch was on ohm and showed 1.000, so it was accurate, no internal problems.
The problem it was, that it was "dirty" inside the meter's connectors.
At the amp connectors, was showing high resistance, in the mega ohms range.
Un-soldered(was not necessary) it and poured some 98% IPA in them and left it over night.
In the morning, the "short" it was completely gone. Re-soldered the connector and it was good to go.
Found this fix at eevblog.
I have just purchased, some better test leads from Prob Masters:
http://www.probemaster.com/product_i...roducts_id=207
It is so much better to use these on tiny components. The tip is much smaller, then the original Fluke one.

[budm]

Re: Toshiba LED TV, blank screen

Take the DCV reading on pin 13, then start by using 100K resistor between pin 13 and GND, take the reading, to see if the voltage does drop down. I do not remember the value of the resistor I use but I end up with around 3.8Vdc on that and it is still bright enough for me and the LEDs stay lit all day. You can use a pot too for adjustment, if the Voltage goes too low you will see the screen flash on for seconds then goes off.
Leave the wire off, see the wire I removed.