I've come across a Pentium motherboard recently that had a dead keyboard port. Whether a keyboard was plugged in or not, the BIOS reported No Keyboard Detected. Not an unheard-of occurrence, I've seen this before with either the keyboard port or the mouse port, when for instance, the corresponding cable was dragged on the floor, got charged with static electricity, which was then discharged through the port connectors. Since the keyboard port functionality on modern PC motherboards is integrated into a multifunction chip that is surface mounted on the motherboard, repair is generally considered impossible... that motherboard is garbage.

Or is it? In my case, the motherboard in question utilized a National Semiconductor multipurpose I/O chip, the PC87306. This chip has two ports that are identical in electrical characteristics; one for the keyboard, and one for a PS/2 style mouse. And I just happened to remember that on some motherboards, when you accidentally plug your keyboard into your mouse connector, the machine still boots up fine, with the BIOS apparently correctly detecting the keyboard even when it's hooked up to the wrong port...

On this motherboard, there was no externally connected mouse port, i.e., the PC87306's mouse pins were unused. It didn't take long to desolder some jumpers and cross connect the keyboard connector to the chip's mouse pins. It's boot time... and I was greeted with a Keyboard Detected message. One poor motherboard just got another lease on life...

With motherboards that have both a mouse and a keyboard connector, you may not even need to do any soldering; you might be able to simply plug the keyboard into the mouse port. Of course you will lose the on-board mouse connector, but you can still utilize a serial mouse, for instance.

A word of warning: this kind of surgery works only with PS/2 style mouse ports. Serial ports, Bus Mouse ports, or other, proprietary mouse ports are not compatible electrically with the keyboard, and using a keyboard with these ports will likely cause damage to both the keyboard and the motherboard. Also, even with PS/2 mouse ports, there are no guarantees that your system's chip set or BIOS will support using a keyboard hooked up to the mouse port; in other words, it worked for me, but it may not work for you.