Some Simple Keyboard Repairs

Written by TAD

(or how to clean crumbs out of your keyboard)


Yesterday I found that some keys on my 2nd hand PC's keyboard stopped working or failed every other keypress. I know this problem is common amongst the more 'messy' coders who think their keyboard is just a glorified plate for their midnight cookies. (We all know that the mouse-mat is the correct place for such meals. GRIN).

I will describe some simple, but useful tips to bring a crumb-filled keyboard back to life without having to send it to be repaired or having to throw it away and buy a new keyboard.

Membrane keyboards.

A common problem with the "plastic nipple" keyboards is that the small round plastic button/switches collect dust or other pieces of food stuff and other CPS killing items (hair, coffee, broken teeth and dust etc.).

First turn off your PC and unplug the keyboard.
I know this is not really, really vital, but just in case.

Turn the keyboard upside down and place 2 objects under it to prevent the keys from being pressed against your desk. I find that two VHS video tapes or boxes are ideal. If you don't do this then after you take the back plate off the membrane you will find that the plastic key "nipples" shoot off because the keys are pressed against the desk. Having to pick up 100+ keys isn't much fun...

Remove the screws from the back of the keyboard.
(Remember to keep these very safe.)

Remove the backing plate from the membrane. Some keyboards have a case-within-a-case where the keys, switches and curcuit board are screwed together as one piece which can be removed from the outer keyboard shell, but most modern keyboards aren't because this pushes cost up. So your keyboard is probably moulded together into a few moving parts.

Examine the plate for dust, cookie crumbs or new lifeforms. Wipe all the surfaces and call NASA if some alien creatures have evolved inside your keyboard after feeding on cookies and dead skin flakes (yummy).

Repairing the membrane.

Now there are two types of membranes:

1. Most are made up from individual "nipples" (100+ of them).

If a nipple is split, then you can't really repair it. A super-glue or other fixing technique will either fail after a dozen presses or clog up making that key totally useless, possibly wrecking the entire keyboard!

One trick which works very well is to swap the broken key nipple with a rarely used key (such as F12, PRINT-SCR, PAUSE, ALT-GR etc.). Because the arrow keys are used so much these are usually the ones which split most often, especially the UP arrow key. You can of course swap UP with KEYPAD-8, or use the keypad as the cursor keys.

If you have a spare keyboard then you can simply replace the nipple altogether and end up with a completely working keyboard for free.

2. The other type is a 1, 2 or 3 piece membrane keyboard.

These have all the individual nipples joined together. This makes life a little easier if you drop the keyboard - i.e. you don't have to pick up and insert 100+ key membrane parts.

If a key nipple splits then you might think that the entire membrane is useless but it can still be repaired. You just have to take a pair of scissors or knife and cut out that key nipple and swap it with another one. I had to do this on my old 80486 PS/2 keyboard. The cursor keys failed, so I cut and pasted some other keys and it worked nicely. You may have to trim the key, but it normally works.

Dirty membrane nipples.

This is not a serious medical condition, but when the tiny, black dots under each key nipple gets jammed with a cookie crumb or dirt of some kind. All you have to do is to carefully wipe the black dots. This should solve the problem of a key not working correctly. Make sure that all the keys are free from dirt, otherwise hitting a key will fail every so often. Believe me, a tiny spec of dust will prevent the key from working.

BEFORE you start to reassemble your keyboard, check all the black dots and clean them if need be.

Wipe the matrix curcuit sheet (the transparent sheet with contacts and lots of tracks printed on it. Anything will do, a duster, tissue, old T-shirt, pair of socks...

Make sure all your key nipples are present in their correct places and neatly seated.

Push the matrix sheet back into place and the backing plate. You may need to remove any connected curcuit board/edge connector so that the membrane aligns neatly under each key button. The screw holes are a good guide to determine whether the membrane is seated in the correct place.

Replace the back cover and screw it back together.

Closing Words

I hope someone will find these tips useful, they are certainly much cheaper than buying a new keyboard (they are mostly FREE!).

If you are thinking about buying a "natural" keyboard (you know those crappy split-M1cros0ft keyboards) then DON'T! IMHO they are really lousy. The major problem is that unlike a normal straight keyboard where you can use both hands across most of the keyboard, you can't on these split keyboards because of the huge gap down the middle. On the old, standard keyboards the Y,H,N,T,G,B,R,F,V keys can be easily reached by either hand which is often handy if you are using the keypad too.

Happy typing.


TAD #:o)