Another acquisition from the swap meet was this HP 85A Professional Computer; while quite limited even compared to most hobbyist PCs of the early 80s, it has a very powerful scientific command-set in its HP-BASIC command interpreter, coupled with HP-IB and other I/O as options. I'd say the best way to describe it would be as "The Ultimate Programmable Calculator".
There are several things that "always go wrong" on these; the printer belts and tapes and tape drive capstan rubber bits all die from age, and the keyboard plastic bits crack from age & embrittlement & morons banging on them.
First thing I found on opening the case was that someone had bought replacement belts, but evidently was a bit gorilla-fisted trying to install them; this screw stanchion for the paper advance stepper was borked.
Not one of the things that "always goes wrong" was one of these paper tape spindles had gotten lost, and this cracked flange that supports the printhead drive cog. Again, I suspect "gorilla-fisted" as the cause; there's also a mounting-screw flange right there with the ear broken off. These bits all mount in place using rubber well-nuts/blind-nuts which had pretty obviously been overtightened for a long time.
After sleeping on it, I contrived to give it a artificial limb by gluing a 3DP bit on it. First step was to score around the broken-off stub so I had a reference to grind flat with my Dremel...
...yielding this which gave me a surface I could use as reference to design a prosthetic for repair.
And here's the printed part being trial-fitted. I need to substitute a m3 x 18mm self-tapper for the original screw; sadly I have nothing with this oddball hex-head, so will use a common Philips button-head screw.
While designing and printing that part, I also designed and printed 2 parts to make a substitute for the missing mate to this paper roll spindle...
All it took was a few licks with the emery board to make the inner spindle turn silky smooth...
...it looks funny because it was designed to be printed flat for best strength from FDM process. Blame Cura for the dickballs.
Perfect fit; the paper now rolls smooth and square. The next problem to solve was that cracked flange; I decided to sleep on it as well.
The next morning I awoke with a plan; after CA-gluing the broken screw-flange back together so I had it for a reference, a couple hours of fettling with a scrap of steel saved from a PC chassis yielded this repair plate. It is designed such that it pulls that crack in the flange closed as it is slid on; I applied CA in the cracks before epoxy-ing it in place.
mnem
Continued in next post...
