The repair on my 1995 ISO Model M has run into an issue that needs the guidance of someone with more experience than myself in these boards.
My unit has had a number of replacement parts from Unicomp: SDL cable, controller board, barrel frame, a handful of flipper springs and membrane. After cleaning up some liquid damage with a conductive pen, everything is working correctly as far as the electronics are concerned, but the keys on the right hand corner [Numpad 0, Numpad . (Decimal Dot) and Numpad Enter] do not work as they should when pressed. All the other keys register a key press at the moment the spring clicks, regardless of force. In these failing keys, however, they only register when pressing hard. It is especially annoying on the Numpad Enter, which is a key I use often.
I have tried all of the following, with no success:
- Disassembling the bolts and starting over with the mounting from scratch, twice. Problem persists.
- Replacing the Mylar membrane (Same as above. I checked it with a multimeter, so it's not an electrical contact issue, and the keys register as they should when pressing on the raw membrane. Issue is mechanical in nature)
- Using different keycaps on the affected keys (it's not a stabilizer issue)
- Replacing the flipper springs with new ones
- Tightening the bolts around the area
- Loosening the bolts around the area
- Trying to adjust the flippers with a toothpick
- Pressing harder on the barrel frame around the affected area.
The space bar is also chattering on some presses, but that's an issue I managed to "solve" using an AHK software script.
I do believe that the issue might be that the rubber blanket that separates the barrel frame from the contact membranes suffered liquid damage, but I'm of two minds about replacing it. Shipping to my country from Unicomp is insanely expensive for such a small/lightweight part, and I'm concerned that it might not be the issue at all, so I'd be paying a substantial amount of money for a replacement part that may or may not work. I'm also wary of removing it altogether: I'm not sure whether the Mylar membrane might suffer damage from being exposed to the raw flipper springs impacting on it.
Another thing, though: my computer is having some weird random reboots from time to time. When I was using a cheap replacement USB rubber membrane keyboard, the reboots seemingly stopped. With the Model M back on its PS/2 port, the reboots have appeared again. Could the board be behind them, for some odd reason?
My guess is that there might be some unshielded component that's causing electrical interference with the motherboard, or that it is drawing too much power from the PSU. I'm aware that either case is very unlikely, but if it is the Model M that's behind the reboots, then a USB Pro Micro converter like Hasu's might stop them.
Is there any help for my favorite keyboard?
