Ok guys, I've got a great news to share with you: my portable now boots! 
Well, sort of. It's still got problems, but we've managed to get something out of it.
Ferrix has managed to get his hands on another portable that exhibits a problem quite similar to mine, so he thought he could probably get somewhere by comparing and swapping components between the two. Here are his results:
1) The portable fires up smoothly and pretty much consistently if it's overvoltaged: apparently putting 7.46V directly on the battery connector manages to keep it alive and happy, but if the voltage is lower it doesn't work.
2) The portable dislikes any additional load on the rails: in order to have a boot, he needed to disconnect both the hard drive and the internal floppy drive; even if just the floppy drive is connected, each attempt to access it results in an almost instant reboot.
Number 1+2 suggests to me there must be something wrong somewhere in the voltage regulation area / power supply circuitry.
3) If both hard drive and floppy drive are disconnected, the system boots but the display shows something like this.
Here's the cursor:
Here's the blinking floppy:
Here's the video of it booting from a zip drive: http://v8.tinypic.com/player.swf?file=nfmd5l&s=8
4) If the display is also swapped with the one coming from the other portable, we get a nice and solid picture:
All this makes me think that:
1) The logic board itself must be working ok: probably no rotten traces or anything, at least not concerning any "major" part of the system.
2) Something must be wrong with the power circuitry, since it needs an overvoltage to get going.
3) Either the video cable still has something wrong, or the display itself is fried.
So, what do you think? Where should we go from here?
Thanks!
Well, sort of. It's still got problems, but we've managed to get something out of it.
Ferrix has managed to get his hands on another portable that exhibits a problem quite similar to mine, so he thought he could probably get somewhere by comparing and swapping components between the two. Here are his results:
1) The portable fires up smoothly and pretty much consistently if it's overvoltaged: apparently putting 7.46V directly on the battery connector manages to keep it alive and happy, but if the voltage is lower it doesn't work.
2) The portable dislikes any additional load on the rails: in order to have a boot, he needed to disconnect both the hard drive and the internal floppy drive; even if just the floppy drive is connected, each attempt to access it results in an almost instant reboot.
Number 1+2 suggests to me there must be something wrong somewhere in the voltage regulation area / power supply circuitry.
3) If both hard drive and floppy drive are disconnected, the system boots but the display shows something like this.
Here's the cursor:
Here's the blinking floppy:
Here's the video of it booting from a zip drive: http://v8.tinypic.com/player.swf?file=nfmd5l&s=8
4) If the display is also swapped with the one coming from the other portable, we get a nice and solid picture:
All this makes me think that:
1) The logic board itself must be working ok: probably no rotten traces or anything, at least not concerning any "major" part of the system.
2) Something must be wrong with the power circuitry, since it needs an overvoltage to get going.
3) Either the video cable still has something wrong, or the display itself is fried.
So, what do you think? Where should we go from here?
Thanks!