View Full Version : Insects and PC/XT Keyboards

September 11th, 2011, 02:18 PM
Whilst running some tests tonight the XT starting beeping more and more. Eventually I got fed up and rebooted - 301. Power cycle, same. At DOS prompt random letters appearing. Switched keyboard, fine. Blasted out original with air duster (which has been thoroughly disassembled and cleaned recently) and then... fine.

Just wondering if it could have been an insect in it or something.

September 11th, 2011, 03:56 PM
Buckling spring keyboards can be quite sensitive to any sort of debris, including the breaking down of the foam sheet inside of them.

Fortunately, unlike the membrane (Model M) version, the XT uses what is referred to as the Model F variant - capacitive sensing instead of membrane contact switching. This design allows for full disassembly without irreversible mods.

I've taken pics of one of these completely and totally disassembled...but this link (http://geekhack.org/showwiki.php?title=Island:5492) details the oddball spacebar stabilizer bar in better detail. Basic idea is to open the keyboard up, take all the keys off except the spacebar, flip it upside down (and keep it upside down or your springs and 'hammers' will fly everywhere) and open up the inside mechanism. Clear out any debris like dead insects or foam that has broken down, reassemble being mindful of the spacebar spring. Reassemble keyboard, then put the keys on last. Tilt the keyboard backwards so keys are facing away from you so the springs will seat properly, otherwise there won't be a proper click and the keys will not actuate properly.

If debris or poorly seated springs are not the cause(s), might be looking at cable or controller failure. Don't trash it if controller is at fault...there is more life left in the rest of the board. I know someone working on a solder-in replacement controller for IBM capacitive boards that gives full USB HID compatibility natively.

September 12th, 2011, 01:31 PM
Thanks very much indeed for such detailed info. It's working OK today, but as you suspect the foam inside has completely degraded.