Month: January 2016

Apple IIc Keyboard Repair

Apple produced three versions of the IIc computer during its production run. These are the A2S4000, A2S4100 and A2S4500. The last one (A2S4500) was the IIc Plus which was quite an upgrade over the standard IIc. It provided a built in accelerator, 800k 3.5″ floppy drive and the entire power supply was now internal although it was limited to 110v only which is a bit of an embuggerance for us in 220v land. The IIc plus and the A2S4100 both had memory expansion connectors that allowed the memory to be easily upgraded but the best feature was that Apple built the keyboard using really nice tactile Alps keyswitches which feel really nice to type on.

Sadly, the earliest version which also seems to be the most common was fitted with a not quite so nice keyboard. If you have an Apple IIc and you don’t like the feel of the keyboard and it’s not as easy to type on as you think it should be, the chances are that you have an earlier IIc with this keyboard. However, it might be possible to make it work better!

Apple made the decision to fit two layers of rubber between the switches and the key tops to stop dust and other bits from getting into the depths of the keyboard. Unfortunately, in the 30 or so years since the machines were produced, this rubber has probably gone brittle and made the keyboard more difficult to type on and even causing keys to stick.

So, on to the fix…

  • firstly, remove the 6 screws from the base of the machine (Two right at the back and the four under the keyboard)
  • Release the clip from the front edge and slowly lift the top up. There are another two clips over the disk drive so be careful.
  • With the top removed, lift the keyboard out, unplugging the ribbon cable.
  • Now, with the keyboard removed you will need to remove each key top. I do this using a flat headed screwdriver under one end and supporting the other end with my finger. The key tops just pull straight off but it is important to keep them level while lifting so as not to break the stem.
  • Once all the tops are removed, the top rubber layers should just lift off. You might even find that it just crumbles apart. The second layer is more durable and can stay in place.
  • I usually give the keyboard a good dust out with a dry paintbrush at this stage and also wash the key tops in some warm soapy water.
  • Once cleaned, simply replace the key tops and reverse the procedure to re-assemble the machine. This should be enough to make the keyboard work a lot better.

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Note: While the above procedure has worked well for me on a number of occasions, other people have still had issues with sticky keys and have had good results by using a light machine oil on the small metal clips on the top of each switch or even removing these clips altogether.


SDK-85 Restoration – Part 1

Released in 1977, the SDK-85 was Intel’s development board for their new 8085 CPU. Unlike the 8080 on which it was based, the 8085 only required a single 5v power source making it ideal for small systems. Along with the 8085, the board contains a hex keypad, 7 segment displays, 256 bytes of RAM (Upgradable to 512 !) and a small monitor program in the 2k of ROM. There was also an interface for connection of a teletype.

One of the nice features of the SDK-85 is it has a large prototyping area for adding your own circuits to upgrade the system. However a downside of this is that when these boards do come up for sale, they often have their previous owners experiments soldered in. This was the case on my SDK-85 that I recently acquired…


This board was purchased on Ebay and came with a couple of extra components & connectors in the prototype area. My plan was to remove these, clean up the board and add sockets for the additional driver & ROM IC’s…

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The images above show the stages of the board clean up and addition of the new sockets. I decided to also change the 40pin socket that had been fitted for the optional RAM expansion. Nothing wrong with it but just wanted one that matched the other sockets. The next step is to add some solderless breadboards on top of the prototype area. This will allow the addition of test circuits & experiments but can easily be removed if I want to restore the back to the original spec. I’ll cover this once I’ve ordered the breadboards 🙂