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TRS Color Computer 1 Keyboard Disassembly

C

clh333

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Feb 22, 2015
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1,443
Location
Cleveland, OH, USA
CoCo 1 Cat. 26-3004 Rev. E board purchased from eBay seller two months ago, Having addressed other issues I now turn my attention to the "chicklet" keyboard which is as poor as everyone said it would be. I don't believe there are any dead keys but some require a lot of pressure, some double-strike and some stick so I need to do something.

Knowing nothing about these I am posting asking for any information, pointers, lookouts, etc. How, and how far, can it be disassembled?

Thanks,
-CH-
 
The keyboard turns out to be a simple matrix circuit board that is contacted by brass "fingers" actuated by rubber domes that act as shafts and springs. I cleaned and reassembled and found most of the issues had been resolved. In the absence of any signal-processing hardware on the keyboard itself it is likely that the CPU is polling the board at some frequency.

-CH-
 
clh333 said:
I read that one of the two MCM6821(P) is responsible for polling the keyboard.
Click to expand...
It’s still the CPU polling it, the 6821 is just an I/O port, not an MCU. (The polling loop activates an output line on the PIA’s second port to provide a column strobe and the value of the row is read via the first port.) There’s no interrupt or anything associated with it and the returned value is just the state of the raw matrix.
 
The cleaning was well worth the effort but came at the expense of one key: I damaged (bent) one of the brass contact "fingers" and had to pick a key to disable. At the moment that is the CLEAR key.

I'm attaching pictures of the contact in hopes that someone has a spare they are willing to part with. If so, many thanks.

-CH-

IMG_4281.jpg
 
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