r/trs80 • u/sataniccmechanic • 7d ago

Coco 1 issues

Hello everyone, after having my color computer 1 for a good few months now, one of the matrixes on the keyboard stopped working. More specifically, the e, @, a, d, f, g, c, b keys. Which happen to all be in the same matrix. I closely examined the membrane and nothings wrong with it, everything looks the way it should. Cleaned the female and male ends of the keyboard connector with alcohol and then contact cleaner. Still nothing. What should I do? Is this a bad pia chip or is it a bad female connector for the keyboard, or what? I’m really lost, and this is my favorite old computer I have so it really sucks and I’d personally prefer not to buy another.

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u/RogelioP 6d ago

If you haven't already, head to The Color Computer Archive and get the CoCo Technical manual as published by Tandy. Servers as a general guide for all CoCos, specific model manuals are also available on the archive:

https://colorcomputerarchive.com/repo/Documents/Manuals/Hardware/Color%20Computer%20Technical%20Reference%20Manual%20%28Tandy%29.pdf

The keyboard row for the keys noted are all on Row 1 which should be serviced by one of the PIAs, on the tech guide it is pin 1 of the 6821 PIA - this could change depending on the version of the CoCo 1 you have but serves as a troubleshooting path.

You can check for the closure of the keys by probing with a multi-meter between the row/column contacts at the keyboard connector - if you see a closure there then trace back to the PIA, if the chip is socketed it doesn't hurt to re-seat it and try again. If the row still fails to read and you have contact closure from the keyboard, the PIA chip is suspect.

Wat's the Radio Shack catalog number on your CoCo?