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Old 11th Feb 2020, 11:21 am   #75
John Earland
Hexode
 
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
Default Re: Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
Well, I dug out an alternative version of the PET circuit from which I have cropped the keyboard scanning circuit, see attached. With respect to the connections between the 74LS145 outputs and the connections to the column pins on the main board connector, they are exactly the same and in fact this version of the diagram has the note 'common to all PET computers' in the lower right hand corner.

Try another tack - with your meter on its lowest resistance range, put one probe on pin 1 of the 74LS145, and hold it there while you touch the other probe to each of the main board keyboard connector column pins 1 through to 10. Only one of those pins should be directly connected to the 74LS145 pin 1, that is, only one pin should show zero ohms between the connector pin and pin 1 of the IC. Which one is it?
Not sure this is the right layout. The 7145 IC is to the right of the keyboard connector on my board this diagram is showing that it is on the left - or have I misread it??
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