Apple Adjustable Keyboard (M1242) keys repeating

[jonpurdy]

TL;DR: keys repeat sometimes, can it be fixed by cleaning switches or is it a design flaw?

Full post:

So I've always wanted this keyboard ever since seeing it in The Net (along with the 8100, PB 540c, etc.). Picked up a non-working but cosmetically great one a few months ago, and a working but yellowed one a month or so ago.

The non-working one had a split ribbon cable (the one connecting both sides of the keyboard). Which is unsurprising since it's very tight and disassembling the keyboard seems to tug on the cable enough that it could split if one wasn't careful.
 

The working one is mostly fine, but I've noticed that some keys have an issue where they repeat (I type "r", but end up with "rr" or "rrr"). Or if tying "the brown fox" I'll get "the ebrrown fooxo" (slightly exaggerated example, but shows that the extra presses still get inserted after I've typed the next character). This typically happens when typing at high speed and not as much at low speed. It's isolated to a few keys, but I've only tested it for a few minutes at a time so the issue could be more than those keys.

If I was to wager a guess, it seems like the key switch is internally sticky, so electrical contact would be held for slightly longer than the split second that my finger hits the key, causing the repeat. (It's not a software setting, checked Key Repeat.)  A second guess would be that the keys aren't debouncing correctly (google "keyboard debounce" for more info).

Is this something that can be fixed? I was planning on getting the key caps off all the keys and cleaning the switches out individually to see if this fixes the issue. I could also pull the keyboard switch parts and circuit boards and plastics from the non working one and use the ribbon cable from the working one. Though I've heard that these keyboards are somewhat flawed from the factory and a lot of them had to be RMA'd when new.

 

[jonpurdy]

Update: was motivated to look into this further this evening. Did some more testing and found that it was specific key switches that were the problem. Some of them (like the "u" key) are softer and activate with less pressure than others. I found that totally disabling key repeat in the Keyboard Control Panel did help. However, I took the chance and swapped the ribbon cable to my first M1242 (the one with the broken cable). Much better performance and the issue with the repeat keys basically went away. Of course, it turns out this keyboard has some issues of it's own: certain key caps require MORE pressure than others, so instead of repeat characters I get no characters at all :huh:

I think the next plan is to figure out which key switches on each are good and bad, then remove or desolder the bad ones and replace them with good ones from the spare keyboard. Lots of links available for this keyboard for anyone else interested:

http://www013.upp.so-net.ne.jp/cyberdog7/Adjustable.html

https://deskthority.net/wiki/Apple_Adjustable_Keyboard

https://applefan.tistory.com/41

 

[jonpurdy]

I was able to fix most of the bad keys on the good keyboard. Swapped a few springs out and one metal piece and the keys were back to normal. There's still one key that's giving me issues ("w") and I intend on desoldering the switch and replacing with a good one.

I also gave each side of the keyboard a very detailed clean with, compressed air, q-tips, and alcohol.

To protect the ribbon cable that connects each side from damage, I filed off a few plastic tabs. These were pressing down on the cable.

I've attached a photo of the switches for future reference.

 

[jonpurdy]

Just wanted to update this post in case anyone is following my path to resurrecting an Adjustable.

I ended up finding problems with a bunch of other keys that couldn't be resolved by swapping out springs and such. So I ended up desoldering known good switches from my parts keyboard (A2) to my good keyboard (A1).

To do this:

• Map out the known good keys on your parts keyboard. Make sure they work reliably every time the key is pressed, and make sure they feel correct relative to other keys.
  
• Desolder the good key switches.
  
•  
  

To desolder switches, you just need to take the top part of the keyboard off, no need to take the bottom apart. And watch out for this hook; it keeps the board in place.



When removing the actual board where the keys are soldered to, remove the ribbon cable so that you don't accidentally bend or destroy it while desoldering. It's stuck in there pretty tight, but with equal pressure on both sides it can be removed (and reinserted). 



Each switch is connected by 4 contact points. Desolder these and the switch will come off.



On your good keyboard, you'll need to desolder the broken switches. Once this is done, take a good switch and place it into the holes of the target key. 



Solder a couple of points. Then make sure that the switch is aligned correctly (it may not be all the way in). 





If correct, solder the rest of the points.



Then just verify that the new switch(es) work once they're all soldered in.

I will update this with a couple more photos and update it for clarity if there are any questions.