Mac 512K not accepting Keyboard input

[ConnahComputerSmith]

Hello! I recently got my hands on a stack of Mac 512K’s, and have slowly been working on repairing them. On one of my units, I managed to get it booting, but there’s two problems: The disk drive accepts a disk but won’t spin, and it won’t accept a keyboard input. I’ll make a separate thread for the floppy issue when it comes time for me to address it, but I’d like to use this thread to get more info on the keyboard issue. The keyboard I’m using is an M0110A, and I know it works, as it works fine on my fully functional 512K. However, when booting the other 512K using a Floppy Emu, the keyboard does not accept any inputs. I haven’t measured voltage and checked for ground at the connector yet, so I’m going to start there once I get the chance (working on other Macs at the moment). I couldn’t find any info on fixing a Mac board that doesn’t accept keyboard input, so I wanted to put this out here to see if anyone has had any similar issues, and could help me save some time by pointing out what to check. Otherwise, I’m going to start by checking voltage and ground as states, and then tracing the lines back to the chips they run to, according to the mainboard schematics (if I can read them).

Thanks for your time!

 

[nathall]

Someone at some time probably tried plugging in a standard telephone cable, which also uses RJ11 connectors but is not electrically compatible instead of the Apple cable. This can fry whatever component on the logic board handles keyboard I/O. I’ve never done it and never had to deal with it, but I’m sure someone here can tell you what component that would be.

 

[bibilit]

Using a telephone cable won't fry anything... but won't work either. Your issue is located on the cable itself (if you are not using the same on both units) or a bad solder joint in the keyboard itself.

the keyboard itself is pretty reliable and easy to fix.

 

[nathall]

Using a telephone cable won't fry anything... but won't work either.

I’ve known several people over the past 35 years who’d beg to differ with that claim.

 

[JC8080]

I had the same symptoms on a 512k. I checked continuity from where the keyboard connectors meet the PCBs on both ends, there were no breaks. I couldn't figure it out, the keyboard worked with another machine, like yours does. Someone suggested cleaning the keyboard cable jack with IPA. I blew this suggestion off because i always checked continuity, so I knew there wasn't an issue there. Finally out of despairation I cleaned the jacks with IPA, and it fixed the problem. I made the same suggestion to someone else with the same problem. They too blew it off, and finally tried it, and it fixed their problem too.

I'm not saying it is a certain fix, but it only takes a few seconds with some IPA and a cotton swab to give it a shot.

 

[ConnahComputerSmith]

Using a telephone cable won't fry anything... but won't work either. Your issue is located on the cable itself (if you are not using the same on both units) or a bad solder joint in the keyboard itself.

the keyboard itself is pretty reliable and easy to fix.

Using the same keyboard and cable on both units, plus I have a spare cable with the same results. Works fine on my working 512K and the Plus I just fixed, but it doesn't work on that one 512K, so I still think it's an issue with the main board. Can't see any obvious damage with the naked eye so I'm hoping it's just dirt on a connector or a cracked solder joint. Still haven't gotten the chance to measure anything as I've been working on fixing a Mac Plus, and want to wait until I can be in front of a camera before I start poking and prodding at my board.

I had the same symptoms on a 512k. I checked continuity from where the keyboard connectors meet the PCBs on both ends, there were no breaks. I couldn't figure it out, the keyboard worked with another machine, like yours does. Someone suggested cleaning the keyboard cable jack with IPA. I blew this suggestion off because i always checked continuity, so I knew there wasn't an issue there. Finally out of despairation I cleaned the jacks with IPA, and it fixed the problem. I made the same suggestion to someone else with the same problem. They too blew it off, and finally tried it, and it fixed their problem too.

I'm not saying it is a certain fix, but it only takes a few seconds with some IPA and a cotton swab to give it a shot.

I'll definitely give that a try! Maybe also fresh solder might help me as well.


Will be posting results once I get around to it