Toshiba 46TL936B No picture or backlight

[johnynoi]

Hi guys,

Im Johny and I've got my father in laws broken Toshiba 46TL963B and learn how to play about with the insides.

My skill level is basic at best. I have an analogue multimeter that I found in the wheel well of my car by chance, although I'm like Harry Potter when he first gets his wand, I can point it at things but have no idea of the consequences!

The symptoms of the TV are as follows:

When plugged into the wall, green power light on front of the TV is on, but thee backlights are not on and shining a torch at screen does not reveal any image (although this is hard to tell because I don't know what I'm looking for when TV boots up).

Unsure if sound is working, again not sure how to cycle through inputs or if even any response from TV.

With the back off, the main board has a green LED that is light constantly.

I have read about firmware problems with Toshiba TV's, so downloaded the following files:

TL_MBOOT_545609.bin
TL_MFC_246009.bin
46TL963K_587542_INIT_CLEAR.bin (where K has been changed to B to match model number)

When plugging USB into TV and powering on at wall, orange indicator light comes on at front of TV as well as green light, and green LED on mainboard flashes on and off slowly.

Orange light on front of TV goes out and green LED on mainboard flashes quickly three times then pause, and repeat ad finatum until TV is turned off at wall. I assume this is the TV failing to read the USB Drive as its an 8GB drive flashed as FAT 32 where it appears a 4Gb or less drive flashed as fat16 is required, unfortunately I haven't acquired a lower capacity drive yet (I did repartition as a smaller drive but still had the same response from TV)

Pictures of boards uploaded and attached

I've tested the fuses on the boards (I think) and they seem to be okay (continuity with ohm thingy on multimeter? I googled that)

I'm open to ideas and can follow basic instruction, which I may need spelling out for my untrained mind.

[Hamie]

Re: Toshiba 46TL936B No picture or backlight



On the above connector monitor the voltage labelled power TV power_tv

First check what the voltage is on standby then press the on button and see if the voltage changes.

[johnynoi]

Re: Toshiba 46TL936B No picture or backlight

Thanks Hamie for the reply, I've just started work so will need to wait a few hours to get back home and try it. I'm embarrassingly a complete novice at measuring voltages, I've got a multimeter but don't know where to point it. Do i unplug the connector and point one end of the probes (black or red?) On the wire end or the board end and the other to the chassis?

[Hamie]

Re: Toshiba 46TL936B No picture or backlight

DC volts.

Black: to chassis.

Red: push the probe down the corresponding wire.

[johnynoi]

Re: Toshiba 46TL936B No picture or backlight

Thanks Hamie,

I pointed the multimeter at where you asked and it came back as 4V (or just under) unfortunately I cant seem to get the TV to go on standby, the green light on the front of the TV stays green

However! I ran the software update again on a smaller drive and by chance I caught the glimpse of "Software upgrade complete" on the screen with the flashlight, so the screen does appear to be working, so its just the back lights that are off!

That's good, right?

[Wabby]

Re: Toshiba 46TL936B No picture or backlight

Backlights off = inverter problem.

[johnynoi]

Re: Toshiba 46TL936B No picture or backlight

A bit more info, I checked the 3 24v led wires going to the LED driver and they all read 24V, and wee white fuse thing on the LED driver seems ok. I've attached some close ups of the components on the board if that helps.

[Hamie]

Re: Toshiba 46TL936B No picture or backlight

Chances are you have an open LED.
It's a very difficult repair as you'd need to strip the panel all the way down to the LEDs.

What voltages do you get going to the LEDs?

[johnynoi]

Re: Toshiba 46TL936B No picture or backlight

I'm not sure I didn't know what connection to try. I'm willing to give it a go though, the worst that can happen is it ends up in the bin where it was going anyway.

I did notice another thread where this was discussed so I've got the better half picking up a couple of the Zener Diodes mentioned in that thread that were successfully used to replace the burned out led.

[Hamie]

Re: Toshiba 46TL936B No picture or backlight

Well good luck let update and let us know how you get on.
Since you've not done it before maybe buy a cracked screen TV form gumtree first and get used to dismantling one.

Word of advice: under the panel are several layers of film and plastic. It's important that they all go back in the correct way or the backlight will look terrible.

[budm]

Re: Toshiba 46TL936B No picture or backlight

You need to report the DCV reading of all (except the GND pins) of that connector WITH the name of each pin next to the reading so we can see what signals are missing.
The two important ones are the BL_ON/OFF, and the PWM pins

[johnynoi]

Re: Toshiba 46TL936B No picture or backlight

Thanks guys, I'll make a start on that when I get home from work.

Hamie, I remember that from dismantling a laptop screen a while ago, I'll lay them out the same way they come off! Once I have all the components off the back and the screen out of the bezels am I better working from glass side or metal rear to get into it?

Budm, thanks for the input, I'll take those readings before I start dismantling. What should I be looking for?

[johnynoi]

Re: Toshiba 46TL936B No picture or backlight

Before I attempt to blindly tackle removing the LED strips, I wrote down all the voltages from the connectors as follows

15 Pin connector from Main to Power suppy
1- (12v) 12V
2- (12V) 12V
3- (GND) 0V
4- (GND) 0V
5- (24VSOUND) 25V
6- (GND) 0V
7- (24V LNB) 26V
8- (GND) 0V
9- (5V) 5V
10- (AC DETECT) 4.5V
11- (POWER TV) 4.5V
12- (POWER SIG) 4.5V
13- (BL ON/OFF) 4.5V
14- (OPTION) 0V
15- (PWM) 1V

9 Pin connector from power supply to LED driver board

1- (PWM) 1V
2- (OPTION) 0V
3- (BL ON/OFF) 4.5V
4- (GND) 0V
5- (GND) 0V
6- (GND) 0V
7- (24V LED) 25V
8- (24V LED) 25V
9- (24V LED) 25V

7 pin connector from LED driver board to somewhere in the chassis

1- (OUT 1) 6V
2- (RESERVED) 0V
3- (RESERVED) 0V
4- (IS1) 0V
5- (IS2) OV
6- (IS3) 0V
7- (IS4) 0V

Hope that's better info for diagnosing!

[johnynoi]

Re: Toshiba 46TL936B No picture or backlight

Another update from playing about after reading other threads.

Noticed that the connector with 15 pins is labelled differently at the point where it connects to the LED driver board, so disconnected the pin at the other side caleld EXT DIM and when turning on at the wall I had a brief flash of light from the backlight before turning off again. Did it a couple of times to see that it wasn't a fluke.

Took the readings from the 4 test points for IS1 to IS4 while turning on with the EXT DIM disconnected and got the following readings (not entirely accurate as only a brief reaqding before falling back to zero

IS1 - 20V
IS2 - 3V
IS3 - 20V
IS4 - 20V

[budm]

Re: Toshiba 46TL936B No picture or backlight

That EXT DIM is the same as PWM, right now using your analog meter to check the Voltage at the LED connector will not work due to your meter is too slow, the output Voltage should spike to >100VDC and then drops down due to the shutdown circuit kicks in.
I will not be surprised if you do have bad LEDS.
http://s807.photobucket.com/user/bud...?sort=3&page=1
This one I had to disconnect the PWM and also set the analog dimming Voltage down (triming the analog dimming control line) to about 70~80% to keep the LEDs on, it will only run for a couple hours at full backlights, but at lower backlights it will run all day. The LEDs in this TV were not completely gone yet so it works, but if your are too far gone then it will not work.

[johnynoi]

Re: Toshiba 46TL936B No picture or backlight

Managed to dismantle the screen and get to the LEDs, the LEDs themselves had no obvious sign of damage but the white connector attached to the strip did seem to have a brown burn mark on it. I've reassembled it just now as I don't know how to test the individual LEDs.

Incidently its a single strip down one side of the panel, right side of the screen when looking at it from the front