Repairing a Sticky Einstein Keyboard

Keys that do not work, or that stick when struck, are a common fault on an Einstein TC01. This guide follows Andrew McRobbie's "Keyboard Skills", printed in Einstein Magazine No. 74 in the spring of 1995, which covers both swapping the whole keyboard and repairing a single key. The steps are his; the notes on safety are ours.

Before you start, switch the Einstein off and unplug it from the mains. It has a mains power supply inside, so never work on it plugged in. Allow about two hours, and read the steps through first so you know which part is which.

Getting at the Keyboard

1. Put the Einstein on a level surface. At the rear are two screws holding the cover, which is also held by lugs at the front, next to the disc drives. Remove the two screws and keep them somewhere safe.
2. Lift the cover clear at the back, then ease it towards the rear to free the front lugs.
3. On the underside, at the very front, are three more screws. Remove those too.
4. Unplug the power light and the loudspeaker from the motherboard; they are on a plug and socket. The keyboard plug can come off now as well.
5. The keyboard aperture is held by six screws in open ended slots. Four of them may be hidden by the disc drives, in which case the drives have to come out.
6. Each drive is held by four small screws, two a side. Slacken them, push the drive towards the rear, and lift it clear of the power supply; the mounting brackets have L shaped slots at the front. Take care with the screws nearest the loudspeaker. You may find it easier to unplug the drive cables first.
7. With the drives out of the way, slacken the six screws holding the keyboard assembly to the base, but do not remove them: the assembly uses slots, not holes.
8. Lift the keyboard cover from the front, with a tilting movement, to free it and the loudspeaker. Note where all the slots are now, because putting it back is the reverse.
9. Four screws hold the keyboard to the cover. Slacken all four, but remove only the two at one end, and the keyboard slides out.

Fitting a Replacement Keyboard

The quickest cure is a new keyboard; Andrew notes that B & H were selling them for five pounds at a show in 1995. Today a keyboard from a scrap machine does the same job. Fit it to the cover with the keyboard's socket towards the motherboard, or connecting it later is a fiddle, and slide the open ended lugs under the slackened screws. Then:

1. Tighten the six screws.
2. Refit the drives, making sure the washers are not trapped behind the mounting brackets.
3. Plug the keyboard, power light and loudspeaker back into the motherboard. Each fits only one way, so no force is needed.
4. Standing at the front, fit the top cover with its front lugs first, then push the rear into place and refit the two rear screws.
5. Take a deep breath, and switch on.

Repairing a Single Key

This is much trickier, and only really practical for a key near the edge of the board: getting at one in the middle without damaging its neighbours is hard. Follow the first nine steps above to get the keyboard out.

1. Remove the key cap, the part with the letter on it, by gentle prising with a screwdriver. Rough treatment breaks the yellow plastic lugs that hold it, and then a new key is the only answer.
2. Remove the solder from the key's contacts on the underside of the board. A desoldering tool that sucks the solder away as it melts is best.
3. With the contacts as free as you can get them, prise the key assembly carefully away from the board. You may need to straighten the contacts first with a small screwdriver.

If the key itself is at fault, you may be lucky enough to fix it by bending its spring clip, once the grey clips holding the assembly together are prised apart. Andrew warns that those clips are so thin they can snap off when you try to free them.

How a Key Works

Andrew calls the Einstein's keys "a master of engineering, but a production nightmare". Two contacts, soldered to the board, are sandwiched with a thin film of metal and an insulator with a hole cut in it. Plastic rivets hold the stack together at the bottom and a spring clip at the top. One contact has a pip on one side. Pressing the key makes the spring clip push a leg on the black mounting, which pushes the metal film through the hole in the insulator against the pip, closing the circuit.

So a meter tells you whether a key is faulty: check for continuity between the key's two contacts on the board while the key is pressed.

Putting a Key Back

Lining the contacts up with the holes can be tricky, especially if a trace of solder is left in a hole, so ease the key in without force. Once it is in place, put a small blob of solder on each contact, and make sure the solder does not run across to the next contact and short out your key or its neighbour. Then reassemble the machine as above.

Spare keys are scarce today. The best source is usually a dead keyboard: Andrew learned how the keys work by taking one apart from a keyboard that came with an Einstein he bought.