Model M Keyboard problem

Well, the case come off easily (but you need a set of imperial nutdrivers), the enocoder PCB, etc, comes off as do the keycaps but the key mechanism is heat-staked together. Assuming it's like the one I repaieed some years ago (and which I have to strip down again sometime), it goes like this : ---------------- My IBM PC/AT enhanced keyboard failed recently -- it would send random characters, go in and out of shift mode, etc. When I dismantled it, I found the problem was mechanical -- the plastic studs holding the membrane 'sandwich' together were broken and the little flaps under some of the keys were out of position. So I worked out how to fix it. Remove the casing : 1) Unplug the keyboard cable at the back of the keyboard 2) Undo the 4 self-tapping screws (7/32" nutdriver) 3) Lift off the top half of the case 4) Lift the keyboard and encoder PCB from the lower case Remove the encoder board : 1) Unplug the tapewire (4 way) between the LED PCB and the encoder and both ends. Set it aside 2) Unplug the 2 keyboard tails from the encoder board 3) Remove the earth braid from the faston tab on the encoder board. Set the encoder board aside. 4) Undo the nut and bolt holding the earth braid from the keyboard backplate. Set those parts aside also. Remove the keycaps. These just pull off, but note that most of the keycaps are in 2 parts. Remove both parts together. Note how the wire loops under some of the larger keycaps (and the space bar) are fitted. Dismantle the membrane keyswitch sandwich : 1) Turn it over, so the metal backplate is uppermost. There are a number of plastic studs that come through the backplate and and melted over to hold the assembly together. Some of these are covered by a paper label, which should now be removed. 2) Break off the plastic studs. In many cases, some of these will be broken off anyway. The aim is to free the backplate entirely. 3) Lift off the metal backplate. If it is distorted (it should be a smooth curve), straighten it 4) Lift off the keyboard layers. In order these are : Lower membrane layer with conductive traces, separator (with holes), upper membrane layer with conductive traces and the LED PCB and a rubber sheet. Keep these carefully in order. 5) Remove the keyboard flaps and springs. Note which holes do not have a flap. 6) Press out the guides that are fitted for some of the wider keycaps. Modifying the upper keyboard panel : 1) Cut/file away the remains of the plastic studs from the keyboard panel. 2) Mark the centre of each stud (apart from those at the very bottom edge, which can be ignored) with a scriber. 3) Clamp the keyboard panel, upside down, to the bench. It can be flattened out by the clamps to simplyfy drilling. Drill each of the marked stud positions with a pilot hole of 1.5mm and enlarge them to 2mm. 4) Tap these holes at M2.5*0.45mm. This is best done from the top side of the keyboard panel. 5) Screw an M2.5*10mm screw into each of the new holes. You'll need about 50 screws. At the far right edge there are 3 holes near the clips for the loops on the '+' and 'enter' keys. The middle hole can't be used, and it is necessary to file down the heads of the screws in the other 2 holes to allow the loops to fit properly. 6) Check the metal backplate can be fitted over the screws. Ease any tight holes with a needle file. Reassembly : 1) Support the keyboard panel upside down over a box. Ensure that all the key posts are clear 2) Insert the flaps, leaving the holes you noted earlier empty. 3) Fit the rubber sheet and the 3 layers of keyboard membrane in the right order over the screws 4) Fit the backplate over the screws 5) Fit a M2.5 washer and nut onto each of the screws. Tighten them evenly, starting in the centre, and then the corners. Then tighten the remaining nuts. 6) Reassemble the guides, keycaps, encoder board and case in the reverse order. The keyboard should now work. Mine does -- I typed this on it. ----------------------- My guess is that you have a similar problem. Broken heatstakes and the flaps for 'B' and 'V' have got dislodged. -tony