Check continuity across that green "P110" SMD. It's a fuse. Perhaps they wanted to bypass it to allow more current to something. Maybe it was done that way after it blew and never reset. The PS/2 port looks barely soldered in there, almost like you could yank it out. Maybe some other kind of mini-din connector (they're prevalent enough) got plugged in which didn't belong there. "It's got S-Video!" So the jack was probably replaced.

I also see "FUSE2" silk screened near the COM1 label. Check and see if that one is not open as well.

Auzner wrote:

Check continuity across that green "P110" SMD. It's a fuse. Perhaps they wanted to bypass it to allow more current to something. Maybe it was done that way after it blew and never reset. The PS/2 port looks barely soldered in there, almost like you could yank it out. Maybe some other kind of mini-din connector (they're prevalent enough) got plugged in which didn't belong there. "It's got S-Video!" So the jack was probably replaced.

I also see "FUSE2" silk screened near the COM1 label. Check and see if that one is not open as well.

Thanks for the fast tip!

Fuse1 (P 110) and Fuse2 (the small white rectanglular bit?) both are open when I do a continuity test. There is also continuity between the fuses and the +5v pin in the mouse port (figured it was worth it to test that too).

I actually took the rest of the pieces off of the PS/2 port since the remaining sleeve wasn't even soldered on (as you mentioned). All of the pins inside look fine. This is the first time I've ever seen the inside of a PS/2 port. They certainly don't look the way I'd expected. Its interesting to think that you can probably swap the different colored ports from other boards since the plastic casings slide free from the pins and hook together like puzzle pieces.

Anyway... I wish I had more knowledge of circuits. I'm sure I could follow these to some point where it would either reveal if there was a problem or not.

Yeah, I think it's that white one. An open circuit is a blown fuse, you want it to beep good, being continuous or closed.

Whoops, I meant closed, not open. Derp. 😵

So, I figured I'd never know what exactly was going on with that wire in place, so I just tugged on it a little and it came loose easily. :p

EDIT: I was misreading something. I'll keep investigating this before posting any more wrong stuff. 🤣

When I check resistance between the +5v pin on the PS/2 connector and the +5v on the ATX socket, it showed some resistance but it kind of bounces around between 3.5 and 1.8 Kohm. Seems to be connected? I think I can probably try it this way without the wire in place, and see what's going on.

Ozzuneoj wrote:

When I check resistance between the +5v pin on the PS/2 connector and the +5v on the ATX socket, it showed some resistance but it kind of bounces around between 3.5 and 1.8 Kohm. Seems to be connected? I think I can probably try it this way without the wire in place, and see what's going on.

Diode drop, maybe?

Looks like some sort of fix of the PS/2 ports. Maybe there was physical damage and they replaced the ports? Looks like they were resoldered on (not very well as you and others also noticed).

I assume you checked, but the way the wire is attached to the board it's bare wires are (almost?) touching other solder points.

The wire was close to touching one other solder point but it was also a +5v. I have removed the wire since there does seem to be some connection to the +5v on the PS2 ports without it. I powered up the board with no CPU and it didn't catch on fire, so I installed the CPU and tried it. The system seems to work fine with a USB keyboard but I cannot get a PS/2 keyboard to work (not sure about PS/2 mouse yet as I don't have an OS installed).

I have a bad feeling that something worse than a single SMD component is at fault here. Where would the keyboard controller be on a KX133 board? I'm assuming it'd be in the chipset, not some separate component.

Reading online I'm seeing a few complaints of bad PS/2 ports from this era, and one from this same board.

Anyway, here's a picture to show why I care about fixing this...

Using a USB keyboard seems to work for most things, including DOS, but if there's an issue with a USB driver in Windows 98 I'm kind of stuck. It seems like the PS/2 mouse port is also dead. Anyone have experience diagnosing problems like this? It doesn't really seem like a power issue, it seems more likely that they tried to run the +5v and it didn't work so they never bothered putting it all back together.

Ozzuneoj wrote:

The wire was close to touching one other solder point but it was also a +5v. I have removed the wire since there does seem to be […]
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The wire was close to touching one other solder point but it was also a +5v. I have removed the wire since there does seem to be some connection to the +5v on the PS2 ports without it. I powered up the board with no CPU and it didn't catch on fire, so I installed the CPU and tried it. The system seems to work fine with a USB keyboard but I cannot get a PS/2 keyboard to work (not sure about PS/2 mouse yet as I don't have an OS installed).

I have a bad feeling that something worse than a single SMD component is at fault here. Where would the keyboard controller be on a KX133 board? I'm assuming it'd be in the chipset, not some separate component.

Reading online I'm seeing a few complaints of bad PS/2 ports from this era, and one from this same board.

Anyway, here's a picture to show why I care about fixing this...

<snip>

Using a USB keyboard seems to work for most things, including DOS, but if there's an issue with a USB driver in Windows 98 I'm kind of stuck. It seems like the PS/2 mouse port is also dead. Anyone have experience diagnosing problems like this? It doesn't really seem like a power issue, it seems more likely that they tried to run the +5v and it didn't work so they never bothered putting it all back together.

I have read about PS/2 problems like these here on Vogons before, but I have never seen a fix unfortunately. Abit 440BX boards seem vulnerable to this.

Good luck with it. That CPU deserves a good board. Send it to me if you can't get it to work (ha ha). 😀