Toshiba LED TV, blank screen

[tibimakai]

Re: Toshiba LED TV, blank screen

It seemed to me that when I was adjusting it, nothing changed on the screen, so you are right, that it runs on maximum brightness.
What size resistor did you use?
I'm a bit confused, on what did you do.
Did you remove the wire, or do you have it connected?

[budm]

Re: Toshiba LED TV, blank screen

With that PWM_dim is disconnected, you no longer have control for the backlights dimming, it is on full blast, the user menu has no idea that the wire is not connected.

[tibimakai]

Re: Toshiba LED TV, blank screen

I have changed it to 75%, but it is still to hot.
I'm thinking, that it would be a good idea, to stick some heatsink on the metal surface?

[budm]

Re: Toshiba LED TV, blank screen

"The right side(watching the TV), it's very hot though." That the LED's strips are getting hot, that is why I lower the backlights level to extend the life of the LEDs for awhile.

[tibimakai]

Re: Toshiba LED TV, blank screen

I have just removed that yellow wire and the TV keeps working. I have left it over night and in the morning, it was still working.
I will keep monitoring for a couple of days, but to me it seems like it is repaired.
The right side(watching the TV), it's very hot though.

[budm]

Re: Toshiba LED TV, blank screen

The analog dimming (not used by TOSHIBA, the TV uses the PWM dimming) has pull -up to full 5V for max backlights level, so I use the resistor (between analog dim and gnd) to drop the Analog dimming line down to about 3.5VDC or so. When PWM wire is disconnected, the ANALOG dim becomes active so you can vary the backlights by varying the ANALOG diming Voltage.
If the PWM line stuck low, then it will force of the backlights off. If you monitor the PWM line and see <1V then the PWM line is not working.
The one shown in the pictures, when you first turn ont he TV, the PWM line show around 4V (it is actually AC 200 Hz PWM, 0~5V pulse, 10% pulse width = min brightness, 90% pulse width = max brightness) which you will see the screen flashes on for second then the PWN drops down to 0V which then the baclikghts go out, in my case I have two problem, one is the PWM signal and anther one are bad LEDs strip that goes out if they driven full on.

[tibimakai]

Re: Toshiba LED TV, blank screen

Thanks Bud, for helping me.
I don't understand the resistor part, though.

[budm]

Re: Toshiba LED TV, blank screen

You can reduce the backlights level to about 75% of max, I was able to keep it running all day, otherwise the backlights will shutdown after about 2 hours.
This one has the PWM control line problem, I disconnectd the PWM line and use the resistor to drop the analog dimming Voltage down to keep the backlights on.
http://s807.photobucket.com/user/bud...?sort=3&page=1

[tibimakai]

Re: Toshiba LED TV, blank screen

I have the same TV, but it runs for hours and eventually, the backlight goes out.
TV still works, sound is working and with the flashlight, I can see the image.
Installed the firmware from Toshiba site, but did not fix the problem.

[budm]

Re: Toshiba LED TV, blank screen

I replaced 2 shorted LED and yes DIM goes up to >3v and then drops down to 0.2v

Try disconnecting the DIM wire and see if the backlights will stay on.

[Agent24]

Re: Toshiba LED TV, blank screen

You right Agent24 found one more that not light up but is not shorted or open, have same reading that the good ones.

If it doesn't light up something must be wrong with it. Maybe it has a broken solder joint or broken\burnt trace? Or maybe it's only failing under load. Try replacing it anyway?

I would assume if that one is not working for whatever reason, then it is the cause of the backlight getting shut down.

[alfredomfr1]

Re: Toshiba LED TV, blank screen

You right Agent24 found one more that not light up but is not shorted or open, have same reading that the good ones.

[alfredomfr1]

Re: Toshiba LED TV, blank screen

I replaced 2 shorted LED and yes DIM goes up to >3v and then drops down to 0.2v

[budm]

Re: Toshiba LED TV, blank screen

Did you replace the LEDs or the LED strip?
Do you also see the DCV at the DIM goes up to >3V and then drops down?

[Agent24]

Re: Toshiba LED TV, blank screen

Did you verify they all light up even if for just one second? Are you sure you did not miss any shorted or open LEDs?

[alfredomfr1]

Re: Toshiba LED TV, blank screen

LED received and installed, LED strip ok now, but still Toshiba logo for 1 second and dark screen.

[alfredomfr1]

Re: Toshiba LED TV, blank screen

I have a Toshiba 46L5000U with same problem: turn on, Toshiba logo for 1 second and dark screen after that.
I disassemble the panel and found it 2 led shorted.
Ordered in ebay for 24.99, will post again when arrive.

[james1095]

Re: Toshiba LED TV, blank screen

A very common cause of this symptom in these sets is failure of the LEDs themselves. They fail shorted which is unusual for LEDs and this causes the inverter to shut down. Unfortunately the LED strip is buried inside the panel and is a real pain to access. You can test easily though, the strip is wired as four series strings of 16 LEDs with a common anode and there are test points near the connector on the inverter. Power on the set while watching the voltage between common and each of the four cathode test points. It should show about 100VDC on each one, if one or more is significantly lower, you have one or more shorted LEDs in the backlight strip.

It isn't unique to Toshiba, some other TVs use the same Samsung LCD panel.

[TechShui]

Re: Toshiba LED TV, blank screen

FW update - well, finally got the FW update working... definitely helped that I could see the screen in order to select 'yes'... learned something maybe useful to others... initially used a usb hanging around... didn't work. It was 8GB and formated NTFS. Found an older usb, 512MB (website said 256MB min) and formatted FAT32. bingo, worked like a champ. results? time will tell, although I have to now figure out how to get the channels happy... some are proper aspect ratio for 46", and other channels seem stuck on low quality with view not going out to sides... will keep all posted, thanks MDLuffy

Where did you download the firmware update from?

[tibimakai]

Re: Toshiba LED TV, blank screen

I have realized that already, that is why I start repairing other type of devices as well.
But still, if I find a nice TV, I can still make a little bit of money, but for sure not like in the past.