Subject: Re: TRS-80 Question

From: Al Hartman <[email-masked]>
Date: Sun Mar 2 10:21:00 2003

> From: Kevin Monceaux <[email-masked]>
>
> The thread has inspired me to pull my Model IV out
> of the closet and fire it up.  Still works great.
> Some of the keys on the keyboard are a bit
> stubborn.  Anyone have any tips for negotiating
> with the Model IV keyboard.  I've never tried
> taking it apart.
>
> Kevin

It's an epidemic!!!

*Grin!*

I can't say for sure this will work, but what I used
to do on Model I keyboards is to pop the tops off the
keyboard, blast them with a little compressed air, and
then a little bit of TV Tuner Cleaner.

IF, the Model IV keyboard is one you can do that with.

If this keyboard has sealed keys, and you can't see
the contacts, you might just have dust and crud under
the keys.

Again, popping the keys and hitting them with a little
bit of alcohol should help that.

Check whatever cleaning solution you use to make sure
it doesn't eat plastic.

Good luck, and enjoy!!!!

Regards,
Al

---

From: [email-masked] (Tony Duell)
Date: Sun Mar 2 14:16:00 2003

> The thread has inspired me to pull my Model IV out of the closet and fire
> it up.  Still works great.  Some of the keys on the keyboard are a bit
> stubborn.  Anyone have any tips for negotiating with the Model IV
> keyboard.  I've never tried taking it apart.

It's a common problem, but the fix is long and tedious. You do have to 
dismantle the keyboard...

First open the case -- one screw on the back, lots on the bottom, then with 
the machine in the normal operating position, lift the top case up, turn 
it counterclockwise and put it down alongside the machine. The monitor is 
in the cover -- take great care not to break the CRT neck. 

Then unplug the edge connector and ground wire (faston tab) from the 
monitor PCB so you can put the top cover out of the way.

Remvove the keyboard bezel (half a dozen screws). 'Friendly' machines 
have the keyboard ribbon cable plugged into the keyboard PCB -- if so, 
unplug it there and remove the keyboard. Others have it soldered to the 
keyboard PCB. With those you have to remove the shielding and a cable 
clamp over the CPU board at the back, unplug the cable at that end, and 
feed it under the disk drives.

OK, you've got the keyboard out. Pull off all the keycaps, including the 
reset button (make a diagram of the positions -- graph paper is good for 
this).

Flip the keyboard over, and desolder (!) all the keyswitches, but not the 
reset button. Make sure all the pins are free. Undo the screws, and lift 
off the PCB. 

Unlcip all the keyswitches from the metal frame.

Nowtest the keysswitches. Measure the resistance between the pins when 
the switch is prssed. A 'good' one is a few hundred ohms at most. Sort 
those out first.

Take the 'bad' ones apart (the housing unclips, then there's a spring, 
plunger, rubber dome with a conductive rubber block inside). Clean the 
parts, particulalry the contacts inside the base, and the conductive 
rubber contact. Put them back together and test again. Any that test OK 
now are classed as 'possibly OK'.

If you still have 'bad' ones, take them apart again, and rub a 6B pencil 
on the conductive rubber contact. That should get them working. But class 
these as 'marginal'

Put the PCB back on the metal frame and screw it in place.

Take the 'good' switches and put them in the most-used places on the 
keyboard. When I did this, I had enough 'good' ones to completely fill 
the alphanumeric area, leaving 'marginal' ones for the number pad (which 
is not essential). And then, as I jsut implied, put the 'possibly OK' 
ones in the slightly less-used parts, and the 'marginal' ones in places 
you can do without.

Solder them all in place (this doesn't take that long!), fit the keycaps, 
reassemble the machine.

-tony