Apple II PLUS Keyboard repair question. Weird problems/Mapping

6 replies [Last post]
Joined: Feb 2 2009
Posts: 61

Frustrating while attempting to repair my Apple II PLUS keyboard.

The keyboard design style is "All in one box" not the individual keyswitch of the older versions of Apple II.

After replacing one of the plastic stem for the "3" key, I had successfully repaired that and it works. But to my horror, I have introduced several additional problems which some keys now produce two characters!

Here's the bug:
"A" key generates "AB"
"B" key generates "AB"
"1" key generates "C1"
"C" key generates "C1"
"2" key generates "X2"
"X" key generates "X2"
"" key generates "V"
"V" key generates ""V"
"Z" key generates "ZS"
"S" key generates "ZS"
"" does not work.
"N" key generates "N" or could be "N"
"" key generates "/"

I don't have the keyboard schematics handy to determine cross shorting on the strobe lines and sense lines that communicates across the 25-pin header between the daughterboard and the keyboard.

Can I have someone with the schematics and techical understanding to evaluate this problem?

Also, when I have to take apart the keyboard, I use water to make the white form sheet (some keyboards use clear plastic form) to temporarily stick to the circuit board while I align and mount the two together.

I am at a loss without the schematics...


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Joined: Sep 21 2008
Posts: 61
Not quite sure what is going

--double post--

Joined: Sep 21 2008
Posts: 61
Not quite sure what is going

Not quite sure what is going on there but here a High Resolution image of the schematic:


resman's picture
Joined: Feb 9 2006
Posts: 214
Check solder bridges or cold joints..

where you replaced the 3. If you are seeing multiple characters from one keypress, the keyboard is generating a bounce somewhere, like a cold joint would. You need a pretty hot iron when soldering on the keyboard because those big traces act like a heatsink and cool quickly.


Joined: Feb 2 2009
Posts: 61
Thanks for this high quality

Thanks for this high quality schematic of the keyboard! It did the trick. I have resolved multitudes of problems ==all caused by the metal tabb-ed switches. One of them was misaligned. The schematics and debugging was a cinch!

Right now that tab that was misaligned has a bwnd I am cleaning up. Hopefully this evening I should be good to go.

Some hints I've learned when opening the "Pandora's Box". Sometimes the screws will strip the threads in the plastic posts when iterating with assembly and disassembly process. Use a fairly thin CA (Cyano-Acrylic A.K.A super glue). Use a toothpick to swirl around a small droplet in the posts. Let dry and away you go! It's as strong as if it was just manufactured. Another trick, I use water to make the space sheet (sometimes plastic or paper form) and align it on the ckircuit board. Use purified/distilled water ONLY. This makes the form stay aligned to the ckt board while assembling. I use two metal pins that fit in the screw post freely as alignment pins. Place each of them at opposite sides of the plastic keyboard plastic posts. Then use those pins to drop in the ciruit board. Works great. Don't fprget to make sure it dries before applying power.

I've learned a few more tricks too, bur too lengthy to describe on this comment.

Joined: Feb 2 2009
Posts: 61
Nope, it's not a soldering is

Nope, it's not a soldering issue. I'm a solder pro. I've soldered pins that are as close as 30mils spaced without bridging issues. No soldering was involved in repairing this problem.


Joined: Oct 9 2011
Posts: 21
Re: Apple II PLUS Keyboard repair question. Weird ...

When I first got my apple ii+ none of the keys except the reset escape and control keys worked. I looked up a schematic and replaced most of the components and the keyboard encoder IC.

Encoder chip that I purchased on ebay did not work it was showing the wrong characters for the buttons like a ? when I pressed any of the numbers etc. I guess it has to be specifically programmed for the computer you are trying to use it on.

Vince Briel makes a product called the super encoder. It's a new production encoder for the Apple ii/ii+ you can use the original keyboard and/or ps/2 keyboard so I couldn't pass it up! it's at I exchanged some emails with him and it sounds like it will do the trick! He's a super nice guy.

I had a heck of a time finding a replacement cable for apple ii+ keyboard to motherboard jumper cord or wire or whatever you call it the dip 16 connector. the pins were very brittle and broke off just by removing the cable. Vince was kind enough to point me in the right direction. Digikey part# C6PPS-1606G-ND. I guess they actually make them when you order them but they are considered "in stock" so they were not on back order and should ship soon and the cable only cost like $2.75.