A31p backlight out, but not inverter or fluorescent ??? PIC

[c0sm0l0gist]

As I was using my A31p, the screen went dead. I could still see that there was an image on the screen if I shone a flashlight on it. Also, the computer worked just fine with an external monitor. So I thought---OK, the inverter board is dead. I got a new inverter, put it in---no change. So now I figure, the fluorescent tube is dead. I took the screen assembly, which includes the fluorescent tubes, out of one of my other A31p's and put that in---still no change. The new screen with the new inverter still behave as if the fluorescent tube is dead. So I figure---maybe the new inverter I bought is no good, so I got yet a third inverter board, put that in, still no change.

One additional piece of possibly irrelevent information---for a few weeks before the screen went dead, once the laptop was on for a while and warmed up, it would decide that the power cable was disconnected even when it wasn't. It would change over to a battery powered state, then after a few seconds it would decide that the power connection was in fact connected after all, and would change back to the external power state. After the screen died, I used it extensively with an external monitor and this behavior did not recur.

My question is this: is there some component on the motherboard that could cause the failure of the fluorescent tube, but leave all other aspects of the computer working, i.e. a power supply output that supplies ONLY the inverter? The alternative seems to be that both of my LCD screens have burnt-out fluorescents, and the second one died just as I changed it.

[hausman]

is there some component on the motherboard that could cause the failure of the fluorescent tube, but leave all other aspects of the computer working, i.e. a power supply output that supplies ONLY the inverter? The alternative seems to be that both of my LCD screens have burnt-out fluorescents, and the second one died just as I changed it.

I'm not familiar with the A31p but the A21p has a small switch on a sub-card that fits into the motherboard. This switch is operated by a protrusion on the bottom of the LCD bezel. When you close the lid, the protrusion pushes the switch and turns off the CCFL. If this switch is broken or the sub-card is otherwise defective or the associated cables aren't seated, etc. that would explain the symptoms you're seeing. Even if the A31p uses a different mechanism to turn off the CCFL it might still be worth exploring it as the problem cause.

[sjthinkpader]

It could be a fuse. I don't have record of which one it is but here is a fuse map for A30/A31:

[c0sm0l0gist]

Thanks for your replies---both things I hadn't thought of. There is a little switch, but it seems unlikely it would go bad while I was actually using the computer.

Update: it's definitely something in the main body of the computer. I swapped the screen components with my other A31p, and the problem is with the body of the computer, not anything in the screen/inverter assembly.

[ajkula66]

In that case you most likely have a blown fuse on the motherboard.

Good luck, you'll need it...