Apple II Plus - Trash to Treasure - Part II

In the last update, we left off with the Apple II Plus able to power on, but without testing either the keyboard or any of the hardware.  After the replacement keyboard cable arrived, I plugged the keyboard in for the first test.  Unfortunately, with the Keyboard plugged in I was getting repeated keystrokes over and over again.  I could tell that the Keyboard was working to some degree because when I'd press a key the correct key would come through, but then fill the screen with repeating characters till the next character was pressed.

I started troubleshooting by doing Google searches on the Internet.  My first understanding from what I'd read lead me to believe that the Keyboard Encoder board could have failed, which is a separate board that is attached too but not part of the keyboard on the Apple II and the II Plus.  I found this modern replacement for the Apple II Keyboard Encoder and ordered it.  The great thing about this solution is that it also includes a PS/2 port for attaching a modern keyboard. With this board and a modern keyboard you have a complete known good keyboard solution for the Apple II or the Plus.  After this arrive and I plugged it in, it had no effect, the problem persisted.

So, understanding that this problem was not with the Keyboard or the Keyboard Encoder board, this pushed me back to looking at and considering the motherboard.  I had read about the book "The Apple II Circuit Description", and so after my failure to properly diagnose the initial problem, I decided it was time to dig in and read this.  I read through the introductory parts of each chapter, and also dug in a bit on the Keyboard I/O schematic.  Feeling a bit unsure after the disappointment with the Encoder board, I decided it was time to reach out on the Vintage Computer Forums.  As has happened before, I received some great advice.  It ended up being one and only one bad 74xx Logic chip, replacing this with a new device solved the repeating key problem!

After testing the keyboard, I determined that four of the keys were not working, the previous cleaning had not been enough to rejuvenate them.  By using the Ohmmeter I was able to determine that the key switch contact was not closing.  Having repaired individual key switches before using a procedure demonstrated on Adrian's Digital Basement, I removed the problem keys by desoldering them from the keyboard, dis-assembling them, and carefully cleaning the switch plates.  These ended up being Alps short-step switches, so the mechanism was a bit unfamiliar.  I found that for some of the switches I had to spray contact cleaner in between the plates, then blow it out with compressed air a couple of times to clear the contact of whatever was preventing the circuit from closing.

After getting a complete working Keyboard, it was time too test the RAM.   I've attached my Disk Controller II card from my Apple IIe, and FloppyEmu to this system, but I did not have any success loading software onto this Apple II Plus, other than successfully loading DOS 3.3.   It turned out that part of my problem was not understanding how the DOS system worked, I needed to go back and read about that, too.  This simple list of DOS commands was helpful.  After I learned that this is a 48K Apple, and that because it's an Apple II Plus, it has Applesoft in ROM and not Integer Basic, then I started to understand why I could load certain programs and not others.

At this point, I was finally able to load and successfully run Apple-Cillin diagnostics on the machine.  Using this tool I was able to diagnose that the machine did indeed have some bad RAM.  By doing trial and error using the first bank of 16K of RAM, I was able to condemn four RAM chips and set aside another group of RAM chips that are working, but their legs are broken. Again, due to the fantastic Retro Computing community's online contributions, I learned that the electronics distributor Jameco still has the correct RAM chips in stock.  I ordered a bunch in order to replenish the top bank to bring this machine back to 48K, and have a few spares as well.

With either 32K or 48K, I can't run most of the Apple II software that's out there from my childhood because most of that requires a 64K machine, but I have the Apple IIe for that.  I think I'll try to outfit this machine to behave as an original Apple II.  Original Apple II prices have gotten a bit crazy, but I did find this cool modern card, a MultiROM card that allows the machine to load Integer Basic, or boot to the monitor and behave just like an original Apple II.  I put this on order, and with the the current situation with shipping during the Holidays, this project will go back on hold for a while.

Thanks for reading!  Let me know in the comments or in email what memories you have of the Apple II, II Plus, or IIe.  One of the things I'm currently researching is what people did with their Apple IIs with less than 64K RAM, what games were popular from the late seventies up till 1981 or '82?