Another one from me sorry, but I think this is worth sharing. I have 2x AST Bravo NB laptops - a mono one and a colour DSTN one. The AST Bravo NB is rare to see these days, afaik it's a Quanta laptop rebranded and you can find a Dell version of it too. This one's not mine but it looks the same: https://wiki.preterhuman.net/AST_Bravo_NB_4/25s
The DSTN one is nearly perfect now but it couldn't detect a PS/2 mouse at all for some reason. The built-in trackball is quite awful to use so it's not been much fun to actually use.
Yeah I could use a serial mouse, but PS/2 mice require less steps and I can use an optical mouse easily. I found that the outer pins on the PS/2 socket (5v and GND) were showing ~0.1v instead of 5v between the two pins.
Taking it apart, my first task was to rebuild a load of broken plastic that held the left hinge in place. Initially I tried gluing the bits plastic from that screwhole back together but then they broke in a new way. So I used a steel washer to make the screwhole's 'base' and crafted some black mouldable plastic that melts in hot water to rebuild it:
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It's stronger now at least, the hinges feel a little less floppy.
Going deeper in, this connector with 6 pins runs the keyboard and mouse PS/2 ports - why is the black wire 5v and the red wire Ground?? Lots of bodge wires too
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Took the motherboard out and followed the circuit around - the 5v trace goes into L37 which goes to 5v. Which no longer has any connectivity, it was that little blue block down by the PS/2 ports.
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That's an inductor which is apparently rated for like 250ma so I can see why it broke running an external mouse / keyboard. I have some 500ma polyfuses left over from my HardMPU builds so the 5v can run across that instead - maybe that inductor was the fuse? Don't think polyfuses existed back in 1993, but it has a fuse now.
Put it all back together and now it detects my optical mouse, much nicer to use.