I recently picked up a nice Science of Cambridge Mk.14 computer from Ebay. While it wasn’t the cheapest purchase ever, it seemed like a reasonable price considering what they usually sell for. Also, there were photo’s of it working – Bonus! The package also included the cassette interface, optional VDU board and an add-on keyboard using proper tactile switches.
Having already used some of Sinclair’s early machines, I knew what to expect of it’s original membrane keyboard. ie, I expected it to be awful and I wasn’t disappointed. Sadly, even though the machine looked to be in good condition, the original keypad was utterly useless (More so than it should have been). A couple of keys didn’t work at all and those that did needed quite a bit of force to work and when they did the machine would register the key-press multiple times.
I plugged in the external keypad thinking I’d have to make do with do with that. It wasn’t much better with the similar problem of the machine registering multiple key-presses. So, to get a usable machine, I had to repair one of the keypads. There were a couple of options. Firstly, replace the original onboard keypad with a new membrane keyboard, fix the 3rd party one or remove the original keypad and solder in some tactile switches. I decided to go with the first option as it would keep the machine looking original and if I wanted to, I could still hook up an external keypad.
Removing the old keypad…
As it was already beginning to lift in one corner, the top layer was really easy to remove. The second layer which is a sort of rubber membrane had pretty much turned to goo and needed quite a bit more work to remove. Once that was done I then cleaned up the board with some IPA.
To make the new keypad, I designed a layout in Illustrator which was then printed on a high quality laser printer and laminated. Once cut to size, I stuck aluminium foil squares to the back of each key location and then attached another laminated sheet using double sided tape. This sheet had holes punched in for each key. the whole lot was then attached to the Mk.14 board using more double sided tape.
Final result. I have a Mk.14 with a keypad that works as well as it did when new. Ok, even when new these keypads were awful. This new one will let me use the machine but its a pretty horrible experience so I guess I’ll still have to repair the add-on keypad.