Toshiba LCD 22BL502B Solid Green Led No Picture

[tanz0]

Hello, first post btw so hello to everyone.

Secondly, I have had a LCD TV (Toshiba 22BL502B) for less than 18 months. Was watching it and suddenly it went dead. No picture, no lights, nothing.

Tested with voltage meter, and found that no DC was coming from power supply board (Vestel 17PW05-3). I bought a replacement board for this, and now, on powering up the TV, one LED blinks red and green alternately around 10 times and then stays solid green. However still no picture. There is another LED which is off.

Fan can be heard to come on. No sound and picture. No backlight.

Does this sound like a firmware problem ? Is it normal for the mainboard to blow alongside power module ? The mainboard is a MB62-2.2 board. I have seen other identical MB62-2.6 boards for sale, I am wondering can I do a straight swap. Do these boards need to be taken from a TV with the same dimensions of screen ?

I am wondering can I reload the firmware, and if so, which would be compatible ?

Thanks, Michael.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

This is a Vestel set, so it's built the same as all the budget brands like Bush, Technika, etc.

Quite a common fault with newer Vestels is bad firmware but it is possible to reload it, you just need a USB stick with the files on it, hold the MENU key while powering up (I believe) and it should copy the files over even if it does not fully power up. Unfortunately finding the files may be difficult.

Could also be backlight fault -- need to test the backlight driver.

Can we have some pictures of the chassis layout so we can see what there is inside and what diagnosis can be made?

I have never seen a small LED TV with a fan!

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Hi, it may not be a fan, but it is a definite hum that comes on whenever the green light goes solid. I did just assume it was a fan I must confess.

I did consider reloading the firmware, but unfortunately this does not seem to be one of the models for which Toshiba provide the firmware on their website. I did manage to find some MB62 files on here but I think they are for use with U-boot ?

Phone has just died. Will post some pictures when it comes back up and I can use camera !

How does one test the backlight ?

Thanks.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Photos Attached.

Thanks.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

OK, along PL706 which goes to the top of the panel, you should have 12V or 24V along pins 1/2 and >2V on pin 3. Do you?
(Black probe on metal chassis, red probe on each pin.)

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Hi, I do yes. I have 12.45v on 1 and 2, and 3.3 on pin 3.

Just to reiterate though, I have replaced the power supply board

Thanks.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

The power board is sending the right signal to the panel so the backlight should be on.

One thing I forgot to mention mention is pin 4 should also measure around 0.5V to 3.3V for the backlight.

Touch the LCD panel lightly, you should see a brief mark appear, if the backlight is on. Do you?

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Hi, pin 4 reading 2.3 v? Is this correct, or should this be reading 3.3 also ? I'm assuming this is TTL logic levels ?

Touched screen gently, no mark appears. Looks like backlight is off. I have turned on the tv in complete darkness though and see no image at all. Would this be the case even without the backlight.

Appreciate the help.

Thanks, Michael.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

That's fine, any where from 0.5V to 3.3V would be acceptable for a dim signal. Probably even less, but can't be sure yet.

So, you need to take that metal shield off the t-con board, which runs along the top of the display, as it looks like the LED driver is under there, and get a picture of it.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Hi, photos attached. I don't see anything alarmingly obvious like scorch marks or blackened areas. No burning smell or anything. Seems like an LG LC216EXN display. Driver board has P/N 6870S-1155A. Does the fact that the backlight is off indicate it is a problem with this board.

Michael.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Thought it may be worth mentioning : Two circular flat objects, possibly caps, marked L401 and L402, looks like some mild charring on them, although could just be from manufacturing process.

Thanks.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

On 2nd thought, looks like inductors. Does this melting around the top indicate the inductors have had it ?

Thanks.

[budm]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

They are inductors, they look OK. You can check to see if the winding is open, you can see the two contacts points on the it.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

There's a small gold fuse on the board, too.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Ah, replaceable, or needs to be desoldered. Is it visible in the pictures ?

Thanks.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

It's this one. Desolderable.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Tested the fuse, seems OK.

My biggest concern is still these inductors. I've taken a shot from another angle, there's some definite sweating on the top, possibly from over current ? Although I suspect this would have blown the fuse.

I've also tested the resistance across the two inductors, they are both initially around 3k, and then drops to 0 ? I'm not sure the resistance should drop this low, might this indicate a short ? Attached another view of the inductors from a slightly better angle showing marking on top.

Thanks.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

The inductors should measure 0 ohms.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Should they measure 0 instantaneously though ?

[budm]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

If I am correct, those inductors are 100uH, so they will have low DCR. Are they on T-CON board?
Inductor sample: about 0.125 Ohm
http://www1.mouser.com/Search/Produc...gTZeTebQ%3D%3D