So I presume you must have received the new 74LS145 today, and swapping this did actually fix the odd fault you had after all?
- It had seemed it couldn't really be anything else, but good to have this confirmed and hadn't had to pay for anything unnecessary
It's probably not been a bad investment money wise (If you exclude your labour costs like they also seemed to on earlier Wheeler Dealers!), especially from noticing some recent asking prices for PET's (especially in the USA) - even higher than >15 years ago.
Although still much cheaper than the various IBM's originally cost in the 80's, until Compaq etc. started off all the compatibles after IBM lost the battle over alternative BIOS's, the hardware architecture was quite open, Plus DOS was sold separately by Microsoft.
I do recall using IBM's OS/2 on our lab's local server for a while but it seemed MS Windows Server replaced that for many after Windows had caught on.
I presume you have tried cleaning again the conductive-rubber plungers, but they still don't work reliably enough.
And had wondered if the conductive rubber can be extracted from the plastic and turned upside-down if it is conductive throughout and not just one face, but is seems the outer non-conductive rubber is also the 'spring' on these. I had seen a PET keyboard completely stripped-down, to clean everything, where they said that was the only way to ensure it was reliable:
https://www.commodorecomputerclub.co...4032-keyboard/
Rather than suggested fixes, here:
https://www.vintagecomputer.net/brow...ead.cfm?id=703 (or the 'silver paint' mixture in that video, which I think was from a Chemtronics? repair kit design for keypads?)
I suppose you could always fit the worst plungers on the less used keys - like the numeric keypad - for now.
So be able to type the Hello World etc. programs easier...