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Repairing Broken Keycaps

Keyboards are easily damaged during transport and most of us have opened a box to discover a couple of keycaps rattling at the bottom. This is a mild annoyance if the keyboard is a popular one for a Mac or PC as a replacement keyboard or keycaps can be cheaply purchased. For damaged caps on an unusual keyboard (like the 1980's Sony word processor one on this page), the only option is to repair them.

Older keyboards use mechanical switches and occasionally the entire switch is broken. Repair requires that the keyboard is disassembled, the broken switch is unsoldered and a replacement is soldered in place. Complete switches are still available from enthusiasts for popular computers such as the Apple II. For less popular computers, a replacement switch can often be salvaged from a broken keyboard from a similar vintage computer. I'm afraid you'll have to do your own homework on locating replacement key switches and disassembling your keyboard. As an example, Tom Lee provides a great explanation of how to replace the switches in a Mac Plus keyboard (PDF, 104KB).

Assuming that the key switch itself is undamaged, you'll commonly find that the plastic stem of the keycap has snapped off. The photo opposite shows the socket in the key switch into which the keycap stem is inserted. The socket in this case is about 4mm by 1.5mm in cross section and about 4mm deep. Extracting the broken stem from the socket requires care and you should use the best quality tools that you own or can borrow. Often you can use a good pair of needle nosed pliers to grasp the remaining bit of stem and pull it out. If that fails, try a better pair of pliers! If none of the broken stem projects from the socket, you might have to drill out the remains. Whatever you do, take care not to damage the switch.

Even if you can extract the broken half of stem, don't kid yourself that you can glue the keycap back together -- it'll fall off again after a few day's typing. With a vice and a few hand tools, you can make a replacement stem in a few minutes. Select a metal or plastic screw that has the same tip diameter as the widest part of the key switch socket. Cut the screw to the required length and file two parallel flat sides until it will fit into the key switch socket with relative ease. Don't worry about the serrations -- they will help to hold the new stem in the socket. If the new stem is a loose fit in the socket, file a few burrs on the flat sides. Finally, remove as much material as you can from the head of the screw. 0.5mm is a good head thickness to aim for.

Remove any remaining bits of stem from the underside of the keycap. Ensure that the replacement stem sits evenly. Now for the difficult bit... After the stem is glued to the underside of he keycap, any misalignment will be magnified when the keycap is refitted. Use a glue that allows you a few minutes to adjust the location of the new stem and use a thin layer so that the height of the keycap isn't affected too much. I recommend using an epoxy glue that won't react with the plastic keycap.

Even though I'd taken a lot of care when gluing my stems to the keycap, I was a few degrees out of parallel. The misalignment is clear in the close up photo opposite although the repair is hardly noticeable when you look at the keyboard in its entirety.

Copyright information: If you wish to use any images on these pages, please contact the author, Phil Beesley on beesley@mandrake.demon.co.uk.