The Artek manual scans are fantastic, and I don't think you'll find better copies than those that Dave makes, but in my mind they still don't beat having the actual original HP paper manual in your hand. The schematics are much easier to read as fold outs rather than either trying to scan back and forth on the computer screen, or trying to print out and tape together hard copies. If I can't get a reasonably priced paper copy I definitely buy scans from Dave, but given the option between a PDF and original paper, IMO there's no contest. (And I have bought about a half dozen of his scans, so I know their quality.)
Perhaps I'm old fashioned, but I still prefer reading things with pages that flip to images that scroll. Especially when comparing things a few pages apart, it's far easier to me to hold the pages and flip back and forth as needed, or stick something in as a bookmark to rapidly get back.
As for your 'new' counter, I personally would definitely do my best to repair it, if for no other reason than it's a cool old piece of technology. If it's been sitting unused in a barn for 20 years, I'd start by looking at power supply ripple. HP used high quality caps, but they may be toast by now. Cleaning the crud off of it would also help to eliminate any leakage paths that might be sending signals astray.
I would be happy to scan or photograph the schematics or sections thereof for you to get you started while you wait for an actual manual copy if you'd like. The power supply isn't terribly big.
-Pat