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Old 10th Apr 2021, 8:23 pm   #1520
ortek_service
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Location: Northampton, Northamptonshire, UK.
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by julie_m View Post
Well, colour me shocked. I would never have expected PET keyboards to have been made using anything but discrete switches.

Anyway, if you are getting keypresses misinterpreted consistently as neighbouring keys, that is almost certainly an indication of a multi-way connector being displaced by one pin (the keyboard is scanned as a matrix of switches; one of the "row" lines at a time is pulled low, and any key depressed in that row pulls its "column" line low. Note that rows and columns here probably do not correspond exactly with the rows and columns of the keyboard); so check all wiring carefully.
Commodore were rather keen on this approach - also used on the VIC20 & C64 etc. But not sure what the (literally from a calculator) 'Chicklet' original was like (But do have one, that no doubt needs some,work, when I manage to dig out an old PET I've got with that on it to fix one day)

Colin's assured us the connector is fitted all OK.
But the keyboard scanning on these is a bit more involved with a 74LS145 4bit BCD to Decimal decoder from the 6520 PIA to the keyboard's scan lines. So knowing how many TTL IC's had failed, that could well be a prime suspect to do some 'scoping on.
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