Toshiba A500 Laptop Backlight

[sean0118]

Hi all,

My old Toshiba A500 laptop has developed a backlight problem. It's almost always off, but if you open the lid quickly it sometimes turns on (but rarely) and then works perfectly until the lid is closed again.

The screen itself works as you can see Windows has booted (but it's just really faint because the backlight is off).

The inverter board uses the MP1010BEM controller, I measured the input to be 19Vdc, however Enable was 0V.

I tested the cable for continuity and its okay, I measured the enable line on the motherboard itself and it to was at 0V too.

I also checked the sensor that detects if the lid is closed. When I activate this with a magnet it turns the whole screen image off (not just the backlight).


Next I took the CFL tube out because I thought the connections on the end might be loose, I haven't cut the heatshrink off but it looks like the wires are soldered on? There are grey bands on each end.


Thoughts on what to do next?


Edit: Forgot to mention, the FT (fault) pin of the MP1010BEM doesn't seem to go anywhere, so I think the laptop motherboard must do the fault detection?

[sean0118]

Re: Toshiba A500 Laptop Backlight

Here's some pics of the inverter board itself. I would test it with a regular household CFL but I don't have a saw to cut one open. :/

[sean0118]

Re: Toshiba A500 Laptop Backlight

I have some test equipment, so I tried hooking up Vin to 19V and Enable to 5V... no luck.

There's two other inputs to the inverter board, I think they go to T/B and BOS. However it's hard to know what voltage/PWM these would require for operation.


Edit: the backlight is about 36cm long, I'm thinking of buying a replacement, do these come in standard sizes?

[sean0118]

Re: Toshiba A500 Laptop Backlight

Okay, I invested in a hacksaw and cut open a 15W spiral household CFL I had.

I then soldered it onto the inverter board output... and got nothing.

The LCD screen still comes on, but the CFL did not light up at all.

Any tests I can do on the inverter board? (I have a multimeter and oscilloscope).