odd diagnostic issue - lcd or motherboard?

[seaweedsl]

I'm trying to fix a T42...p and sorting things out with two t42 ATI motherboards and one flexview UXGA LCD. I'm having trouble with all three. It's weird - one motherboard (a 32mb ATI) is failing somewhat, USB ports going to 1.1, some display issues (goes distorted sometimes) so I swap in another MB, a firegl 128. But no LCD display on that one. Huh? It was just working.with the other motherboard. So I plug in an external monitor and it displays fine. Well, then it's the LCD not the motherboard, right?

So I hook up the other, failing motherboard back again to the very same LCD, and now the LCD works fine again. So is the 128 ATI motherboard bad too? But it does work fine on external monitor.

In sum, one board works external and internal monitor. The other board only works on external monitor. Which is bad, the motherboard or the monitor?

appreciate any thoughts on this one.

Steve

[rkawakami]

Sounds like both ATI motherboards have the typical solder ball failure with the GPU, along with a Southbridge problem which can cause the USB 1.1 speeds. There are separate signal paths for the LCD and external monitor. It's completely possible that one will work while the other does not. The LCD panel is probably okay since it works with at least of the boards.

[seaweedsl]

Thanks mucho, Ray. I had always thought/heard that if an external monitor worked, that indicated that the GPU was not the issue. Now I know! Actually, this is the second t42p (R50p) I've had this summer to do this. I was sure it was the LCD on the other, which puzzled me as it was not the inverter and I'd swapped out the CCFL earlier but now I know better.


Steve

[Neil]

There is also a tiny fuse near the LCD connector, that if open, will shut power off to the LCD panel. F7, maybe, not sure. That could be the problem with the FireGL board. Could well be as Ray said too though.

[seaweedsl]

There is also a tiny fuse near the LCD connector, that if open, will shut power off to the LCD panel. F7, maybe, not sure. That could be the problem with the FireGL board. Could well be as Ray said too though.

Thanks for the reminder on that possiblity. I think I got those fuses checked out now and no luck.

cheers,
Steve