This is an ALPS keyboard. Somebody at Erik's site mentioned that it is
possible to coax a single keyswitch out of the unit by desoldering,
squeezing some tabs near the top, and then lifting through the metal
It is. There are a couple of locking tabs that you sqeeze inwards to free
the switch. In fact that's how you get the switches out if you desolder
the lot and take the PCB off.
My view is that if you have about half the switches defective (as you
seem to), then you probably should take the whole thing apart, test the
switches, etc. You can test them in place (an ohmmeter between the pins,
then press the key), there anre no other components to confuse the
plate. As things stand now it looks like I need at
least 30 key switch
mechanisms .. it might be more practical to construct a replacement
keyboard and hand wire it.
As I mentioned, it is possible to take the swtiches apart and clean the
contacts and/or coat them in a bit of pencil graphite. But how long it'll
last I don't know. I did it to mine, they're still working _but_ I put
them in places where I'd not really use them (I rarely use numeric
keypads, so I put the bodged switches there). You;'ve got far too many
duds to do that, though.
(I'm naively thinking some new Cherry switches, a
sheet of plexiglass,
and a lot of wire. Not a pretty modification, but it gives me a new
keyboard with switches that I can replace. Has anybody done something
like this recently?)
Not recently, nbut I have done it. The main problem with doing it on the
M4 is that IIRC the scan lines are the CPU address bus, suitably
buffered. Which means a lot of HF noise flying around (the scan lines are
thus toggling all the time, even when the keyboard is not being read).
THere has been talk on the list of using a microcontroller to interface a
PC-type keyboard to a machine that expects a matrix of switches. Whether a
microcotroller could keep up with the Z80 address lines and correctly
output the keyboard data or whether you;d need a separate crosspoint
switch chip (which is what I'd probably use anyway) I don't know.
I don;t know what drives you have (Tandon TM100s
were fairly standard),
but if you take them significantly apart, you'll need an alignment disk
and 'scope when you come to put them back together. Again, something that
doesn't worry me _at all_ now, but it might be a problem for you.
If you want to take the drives apart to clean them, let me (us?) know the
model number (or any markings on them). I can then give you an idea what
what you can take off without losing the alignment.
Texas Peripherals 10-5355-001. The inside of the case was fairly good,
Which, IIRC, are a very close clone of the TM100. To the extent that
most, if not all, parts interchange.
thanks to all of the extreme shielding that Tandy put
in. I cleaned the
drive head and rails, and lubricated the rails with a teflon impregnated
oil. They are quieter now.
I'm not going to go much further than that without a scope and alignment
If these are TM100-a-likes, then the postiioner mechanism is on a little
subschassis which you move to do the radial alignment. I've had great
success in scribng a line to indicage the position of that subchassis on
the main chassis, then carefully turning hte adjusting cam screw _without
loosening the positioner fixing screws_ and scribing the limits of its
travel on the positioner unit. When I put the positioner back in, I line
up the marks, get the cam screw to have the same limits of travel, and
clamp things up. I then put an alignment disk in (:-)). Every time I've
done this I've been well within tolerance on the alignment disk.
On the other hand, I'd probably not risk it if I didn't have the
alignment stuff to hand.
Now, the index timing is pretty unimoortant, so it's OK to take off the
upper clamp arm. Of course you can remove the spindle motor, belt,
spindle, beaerings, etc.
If you want to remove the track 0 switch, again mark the position first.
I've never had any problems getting that back right. Those swtiches do
fail sometimes, amazingly an identical part (it's a low operating force
microswitch, about 15g IIRC), is available still.
disks. If these drives go bad I have double sided
drives from the PC
family that I can use, or I will convert to use double density 720KB drives.
Perhaps I'm odd, but I like to keep machines as original as possible.
Which includes keeping the origianl drives, PSUs, etc.