While discussing with someone I know about the Apple II+ and a pair of machines I revived earlier last fall, they mentioned that their own II+'s keyboard had "a few" defective keys and that they hadn't been using it much since. I offered to take a look and retrieved the ailing machine a few weeks later.
This substantially upgraded A2S1016 from the 36th week of 1980 sports a Datanetics 01-0551-01 keyboard, Apple part number 605-4117 dated from August 20, 1980. I took care of its Rifa filter cap, two electrolytics and a few cracked resistors in the power supply as well.
Cleaning flux was a bit of an afterthough in those days... (And for a few more years still, I've seen AEK IIs caked in the stuff.)
After running the keyboard test in Apple-Cillin, it turns out that the definition of "a few" here is twenty-one defective switches out of fifty-two, oof.
My multimeter agrees, no continuity even after exercising them a bit. A quick search tells me the contacts are supposed to be sealed so spraying contact cleaner directly in the housing won't do much. Oh, and the shell is "ultrasonically welded together" per https://telcontar.net/KBK/Datanetics/DC-50.
Cracking one of these open isn't without risk and one or two switches didn't survive:
After four decades the contact membranes are no longer sealed and there is some kind of contamination that prevents the contacts from closing:
It is possible to separate the membranes further to spray contact cleaner to "fix" the switch, gingerly reassemble all the parts then close the shell halves with a bit of polyimide tape - but I'd consider those on borrowed time.
To sum things up:
- Replacement Apple II keyboards of any kind are getting harder to come by and when they do show up they're not cheap.
- The Cherry MX based kit from ReactiveMicro is out of stock with no ETA.
- Datanetics switches are failing fast even though this machine is normally located in a climate-controlled office and there are no signs of spills.
- There are no replacement Datanetics switches available anywhere I checked.
- The Datanetics switches, while not outright terrible, are nothing to write home about in terms of key feel.
But I had an idea:
The Cherry MX switch footprint fits completely inside of the Datanetics' one! (That's a cheap Greetech clone I had lying around.)
Granted, Cherry's design is a decade newer (1983 vs 1973) but I'd still call its linear variant "period correct"; it has proven to be reliable, is easy to clean if needed and it's still in production.
So after getting my first 3D printer, many iterations on TinkerCAD...
...and print attempts in both PLA and PETG...
I'm happy with the results!
Whole keyboard with the "switch adapters" - I went with genuine Cherry MX Black:
With caps back on:
I have attached my model files here and also on Thingiverse (https://www.thingiverse.com/thing:5780203) - they're licensed under Creative C0mmons CC-BY-NC-SA: https://creativecommons.org/licenses/by-nc-sa/4.0/.
You'll need a reasonably well adjusted printer, I used PETG for my final prints and I suggest you do the same, PLA's weaker inter-layer bonds is not ideal for the DC stem in particular. The switch adapters need supports, the keycap ones don't.
Let me know if you end up using my models or if you have any questions.