Lisa 2/10 keyboard not working - looking for troubleshooting advice

[xevro]

I have two Lisa 2/10 computers. One belongs to someone I'm helping with a repair, and the other is my own Lisa, which I bought in May this year. I don't remember testing my keyboard when I first bought it, so I'm not sure whether it was working back then because I had to do maintenance on the power supply which took some time.

While working on the Lisa I'm repairing, its power supply failed and shut the computer down unexpectedly. I've since repaired the power supply. I also installed a Sigma Seven Systems X/ProFile interface and got LOS 2.0 running. However, I discovered that the keyboard doesn't work. I tried connecting it to my own Lisa 2/10 as well, but it didn't work there either. This makes me suspect that the keyboard itself is faulty.

I've tried measuring the keyboard signals with an oscilloscope. When I press the keys, I can't see any noticeable signal being generated; I only see a signal around 900 Hz, which seems to be coming from the Lisa. I'm wondering what else I could check. I could ask the person I'm repairing the Lisa for to lend me one of his working keyboards, which would help determine whether the problem is with my keyboard or the computer.

I also read that the conductive silver pads inside the keyboard can deteriorate with age. If that's the problem, would I expect at least a few keys to still work, or could all the keys fail at once?

Finally, would it be safe and useful to test the keyboard by touching the contact points directly on the PCB with my finger, to see whether the Lisa registers a keypress?
Any advice on further troubleshooting would be greatly appreciated!

[ried]

If the "foam and foil" pads have never been replaced, they're not going to work. Even when stored under ideal conditions with very little use, that 40+ year old foam is no longer going to be creating enough pressure for the foil to contact the PCB pads.

Here's what you need: https://texelec.com/product/foam-capacitive-pads-keytronic/

[AlexTheCat123]

Finally, would it be safe and useful to test the keyboard by touching the contact points directly on the PCB with my finger, to see whether the Lisa registers a keypress?

Yeah, that's a perfectly valid/safe testing strategy. The foam and foil pads are almost certainly the problem, but touching the contacts and making sure the actual PCB works will definitively confirm it.

[stepleton]

You might want to make sure first that you haven't built up a static charge on your person that could go "zap" the moment you touch one of the keyboard PCB's pads --- especially if you're wearing clothes that easily build up a static charge, or if you're working in a room with a carpeted floor. One of the easiest ways to dissipate a static charge relatively safely is to touch the metal shield surrounding any external serial or parallel port on the back of the machine. (The little thumbscrew knobs at the top of the rear panel may also work.)

If you feel a small static shock, then you'll know that you may well have saved your keyboard by "grounding" yourself first. But even shocks that can't be felt are still strong enough to damage electronics.