Looking for TRS-80 Model III Parts/Advice (fwd)

From: Jason Willgruber <roblwill_at_usaor.net>
Date: Sat Dec 12 20:38:07 1998

>If you want to try to repair a keyswitch, then try the following.
>You can unclip the 2 parts of the housing at the sides. The top part
>lifts off, releasing (in order) the plunger, a spring and a little rubber
>dome. The contact is the black (graphite-loaded) rubber pad inside the
>dome and the 2 metal contacts in the bottom part of the switch. Clean the
>metal contacts with a cotton bud and isopropyl alcohol (propan-2-ol). You
>can try rubbing the rubber pad on very fine (1000 grit or finer)
>wet-n-dry paper.
>Put the switch together. Measure the resistance between the pins when
>it's pressed down. You should use 2 pins diagonally oposite each other
>for this test. A good switch is about 50-100 Ohms. A useable one is
><300Ohms. More than that, and it probably won't work. If you have all the
>switches out, put the worse ones on the numeric pad as above.
>If you still have a defective switch, then try rubbing a soft pencil (I
>use a 6B) on the rubber pad inside. That got my worst swtich useable
>again. There is a special kit for this from Chemtronics which recoats the
>rubber contacts, but it's not cheap ($30). It could be worth using if you
>can't get the switch working any other way.

Sure that's a model III keyboard? The keyboard on my Mod. III has actual
metal contacts in the switch that are pushed together by a tab when the key
is pressed.

>Putting it all back together is the reverse of dismantling it. Take great
>care when putting the Model 3 case back together - it's possible to break
>the CRT neck on the logic cage. And while it's possible to replace the
>CRT, new ones are not that easy to get.

The CRT was blown out in mine when I got it. Replaced it with one from an
old RCA 12" B/W TV. Works fine. Where I live, the local thrift store
usually have at least 2 or 3 B/W TV's at a time. I picked up the one I used
for $2.50.
                 -Jason Willgruber
                  ICQ#: 1730318
Received on Sat Dec 12 1998 - 20:38:07 GMT

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