Recently I bought an Apple IIc with german keyboard and after some days of use the RETURN, ENTER and ARROW UP keys stopped working. I opened the Apple IIc case, unconnected the keyboard flat cable and visually checked for some damage, but all seemed to be correct. I applied Contact Cleaner (zero residue) to all the switches and after re-installing the keyboard again all the keys started to work.
Today, after a couple of weeks using the Apple IIc, the problem has come back. What can be cause? Flat cable or keyboard controller chip maybe (which one in this case)?
The fact that contact cleaner helped remedy the issue at least temporarily would tend to indicate it's a physical switch issue and not a cable or encoder issue.
The easiest way to confirm that it's the switch causing the issue would be to take the keyboard out and check the suspect keys with a multi meter in continuity mode to make sure it beeps when you press them. If it doesn't, then it's a switch issue. If it reliably beeps, then you have an issue else where.
Thank you for your advise, I'll do, but it sounds strange to me that the 3 keys have the problem exactly at the same time... I'll see...
After checking with the multimeter, the PCB tracks and flat cable are OK so, I was thinking that the problem was the IC keyboard encoder. I also discovered that after turning off the Apple IIc and waiting around 2 hours, once has been startep up again the keyboard normally works. Then, after around 15 minutes turned on, the three keys stop to work. It's crazy!
I released the drive unit to gain access to all the ICs in the motherboard, and after checking with the finger over the ICs I don't found any abnormally hot. While doing this I realized that the Apple IIc was turned on for more than 40 minutes and the theree keys continue working. Resuming, I realized that when the drive unit is released from the Apple IIc there's no problem and the keys work after 6 or 7 hours with the compter turned on so, it seems clear that the problem is the drive unit but I cannot imagine how can cause this kind of "delayed" problem in the keys.
Maybe I have a ghost into the Apple IIc? Should I use the Apple IIc without the disk drive?
Problem solved.
The last owner of the Apple IIc removed the cardboard between the bottom metallic shield and the PCB, and when the keyboard connector on the PCB is lightly pressed it contacts with the bottom metallic shield and therefore some keys do not work. I'm lucky, this can be caused a shortcircuit in the motherboard.
As I do not found the cardboard, I released the metallic shield and now the Apple IIc works like a charm.
What metallic shield? I own and have opened up two //c's, and there is no metallic shield outside of the drive and the internal power converter box. Not have I ever seen one in any //c disassembly guides.
Hi, I refer to the metallic shield on the bottom of the Apple IIc case. Between this shield and the PCB there's an isolating cardboard. If you don't removed the cardboard you're not able to see the metallic shield under. Here's a picture:
IMG_0953.jpg