Toshiba LCD 22BL502B Solid Green Led No Picture

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

You'll have to forgive me I've seen this term 'T-con' used a lot but not entirely sure what this is. Is this the LED driver board, in which case yes this is the board the inductors are on.

The inductors are reading 3k and then quickly dropping to 0. Both of them have same behaviour though so it's unlikely this is problem. They do look somewhat burnt though. Any way of verifying exactly what problem is. Where would be a valid test point on driver board to check the current is getting past this point in circuit.

I have tested the current across the fuse and multimeter indicates connection is good. Are there any other common faults with this board ?

Having tested outputs on PL706 are correct, can we rule out mainboard/firmware problem ?

Michael.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

100 is possibly 10uH too, if it is 10x(10^0).

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Hello, just wondering how, if at all, can the led driver board be replaced, the various ribbon cables seem to be attached to both board and screen. Although I do see led driver modules on eBay.

Michael.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

I read somewhere here that it is possible for a T-CON fuse to be defective, but still pass current, just during operation the resistance increases until the board fails to operate, instantaneously of course. Is this true ? Also hear some discussion around using 'ice spray' to diagnose bad components ?

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

The t-con is the board currently being worked on; no it can't be replaced due to it being bonded to the LCD panel.
Your suggestion of intermittent fuse is possible; to test it you could measure the voltage on both ends of the fuse, if it is 12V and both ends the fuse cannot be causing the fault.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Thanks. Jumping back to the inductor problem speculation previously discussed, it's noticeable that the T-con protective cover has a small window cut out for just these two inductors. Precisely the correct size for inspection and or heat dissipation. I'm wondering then are these components prone to fault. I've seen others speculating about faulty inductors here but there seems to be a consensus they are rarely the culprit.

I intend to borrow a meter and measure inductance directly.

Thanks.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

One more thing. Finding it difficult to test these parts since they need to be grounded on the chassis to operate correctly. However the chassis prevents access to the t-con board and the cables aren't quite long enough to reach when chassis is moved elsewhere. Do the boards generally have a ground line soldered to them each, both power supply and mainboard, when being tested.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

The inductors are probably not causing the fault. Failure rates of inductors are very low, they consist of coiled wire and a magnetic coil. The main failure mode is for them to fail open circuit but AFAIK you tested that did you not?

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

I did yeh, I was speculating though the wire could have fused at some point along the coil, which would fail closed circuit, but would alter inductance. In any case it's prob unlikely this would cause total blackout.

I'll need to test the fuse when it's in operation.

Cheers.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Hello, I have tested fuse, there is a steady 12.45v across both ends so I don't think this is the problem.

Can anyone tell me what the correct voltages should be for backlight connection. I have com, and ch1-4 marked on board.

12.45v between com and chassis, 3.3v on ch1-4.

Does this look like a backlight problem ? I can see absolutely no picture when it is on during day in bright sunlight.

Thanks.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

For a 22", much higher, around 30V for one pin, low voltage on each return pin. Good news is there doesn't look to be any shorts on the LED strip, that can be ruled out for now then, so it is somewhere on the t-con.

Looks like the boost converter taking the 12V is not working. There is a chip next to the LED connector, what is the part # on this?

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Hi, which chip do you mean ? There are 3 in the vicinity.

One square to the left, looks around 40 pins or so. One rectangular above, 8 pin. And one rectangular to the right, around 20 pin.

Square one looks like OISWL-0058A. I could be a one of course.

8 pin looks like st 404rp ?

Thanks.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

I mean the one closest to the connector going to the LEDs. The one you measured 12V, 3.3V, etc on.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Hi looks like b0926-1efv. Also has 130-ht4 on it.

Thanks.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

I see 4 small components adjacent to the chip. Do these boost converters use external caps for charge pumps ? Will try an find out, those model numbers return no results. Even trying to see the model numbers with a magnifying glass is difficult. And I have 20/20 vision, apparently.

Thanks. In the event of this chip itself gone, I take it that it is game over, how could you swap this component out, hot air soldering iron ? Caps look potentially feasible.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Think that's bd926-1efv

Rohm led driver apparently. What are the common problems that develop with boost controller ? Caps burn out ? You could do a hot air rework of the chip ?

Thanks.

[tom66]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

The topology is an inductive boost converter,


It seems that IC fails often from a little googling, but no-one has a datasheet. You can replace it with some skill, or you could probably use an external LED driver.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Ah, cheers thanks. Just to reiterate though, I see no picture on screen at all in bright light, you're convinced that this is the only problem with the t-con board ?

Thanks.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Having great difficulty trying to get a datasheet for this screen.

I have managed to find an external led driver that looks suitable to drive backlight off existing 12.45v, however it has 4 connections, including DIMMER control and standby.

The backlight connection on the LC216EXN has 6 pins, I'm wondering do you know what these are for. As previously mentioned, they at labelled COM , CH1-4 and I assume GND.

[tanz0]

Re: Toshiba LCD 22BL502B Solid Green Led No Picture

Link to driver btw:

http://uk.farnell.com/midas/ledv1/le...all/dp/2219006