Related to my other post regarding the repair of my Apple II Rev 0 computer at this link https://www.applefritter.com/content/my-apple-ii-rev-0-psu-info is my solution for fixing keys that did not work.
After powering up the computer with no I/O cards, I hit Reset and got the expected VGA dispaly. I did a key test, pressing each key down the rows of keys and found some keys didn't print on the screen, and some keys bounced resulting in several characters being printed on the screen.
When trying to type in the familiar Monitor command to do a memory test I found that six keys didn't work 98% of the time. I eventually succeeded in entering the command line and found about 8 memory location errors. I decided to focus on the keyboard first.
I had the case/keyboard already removed from the main board/case bottom, so removing 4 nuts holding the keyboard PCB to the case was the next task.
This first photo shows my key continuity test setup with my Fluke set to low impedance and to audibly beep on a short circuit.
I clipped a two pin male lead connector from an old IDE drive connector and cut off the plastic lips that surrounded the two pins. The two pins where the same distance apart as the key solder pads on the PCB. This made for easy probing of each key, holding the two pin probe in my left hand and against each key pad and with the keyboard sitting on its edge. This left my right hand free to press the key being tested. The squeeze bulb shown below is what I used later to dribble a few drops of 99% Isopropyl alcohol into the keys found faulty.
Here is my testing setup:
When I found a keypress that didn't produce a beep I marked that key with a black Sharpie pen on the pad side of the PCB. Keys 7, 51, 50 and 58 are shown "marked" here.
With the keys with no or intermittent contact I then filled the squeez bulb with alcohol and dribbled some drops at the edge of the white plastic "push-button" and the black plastic base, shown here:
Immediately after dribbling alcohol into the key I depressed the key(s) multiple times to give the alcohol a chance to clean the contacts. When I then probed the defective keys again they all made good contact.