View Full Version : IBM Model F keyboard "fix"

September 1st, 2017, 05:44 PM

I have a IBM PC XT Model 5160 with original Model F keyboard with capacitive keys. I have struggled to make the keyboard work, however, the keyboard is quite unreliable.

In particular, before I fixed it, the error "3B 301" would appear upon POST, which shows that the F1 key was "stuck" when it clearly wasn't.

I have come up with a fix, but it is not a particularly elegant one and may eventually break the keyboard. When reassembling the keyboard, the actual keyboard unit is placed back into the white case, the cover put on the top over the keyboard unit, and then the keyboard is flipped over and the two screws are inserted into the back of the keyboard to hold the case together. I have found that before placing the actual keyboard unit back into the case, an insulating object should be placed below the little circuit board that sticks out of the keyboard unit (that contains the 40-pin 8048 microcontroller) so that when you place the keyboard unit over it, the object underneath applies some force to bend that little circuit board upwards. In my case, the insulating object is a piece of PVC shower pan liner rubber rolled up to be about a 1/4" thick. Over time, material creep compresses the PVC rubber and I have to reopen the keyboard and roll up the PVC again and replace the keyboard unit. Because of the force applied by the PVC sheet, it takes a little bit of force to push the case close and screw it back together.

If you are having this problem, you can test to see if this works for you by manually bending the little circuit board sticking out of the keyboard upwards as you boot your XT. If the error message goes away, you can try this fix. I hope this helps anyone with the same problem. While the model F keyboard has a great feel, it is a pain in the butt to fix and maintain. Its not surprising IBM changed the mechanism with the Model M.