Message #1 Posted by David Ramsey on 11 Nov 2011, 11:37 a.m.
Since both units are now completely functional, it's time to rip 'em apart, rebuild the power supplies, clean, and paint...
But opening things this old up always reveals more work to be done that you didn't plan on. For example, the plastic socket at the neck of this CRT was (very) loose and starting to crack. We can't source a new socket, so liberal use of High Tech Adhesive™ will fix it in place permanently.
The underside of the main board has even more components on it. They all look OK.
Here are the (burned out) incandescent display stack label backlights. Decades of heat from these bulbs has warped the plastic film with the actual labels on it, and burned away or faded some of the black backing. This has been repaired and replacing these bulbs with LEDs will remove the heat issue. Care has been taken to preserve the original bulb sockets so that future collectors could replace the LEDs with bulbs again, although it's likely that even micro-incandescents like this will be illegal in our dystopian future.
The power supply has what appears to be a half-wave rectifier with capacitor-smoothed output. These two dinky diodes tested OK, but you know? They just look weeny and unsuitable for a Real Man's Calculator, which the 9100 definitely is. (And what? Couldn't HP afford two more diodes for full wave rectification? But so much of the 9100's operation seems to depend on electrical things we'd call "side effects" these days that it's probably unwise to functionally revise anything...)
There! Much better. To those who might complain that this was completely unnecessary, I simply retort that Art is always misunderstood by the hoi-polloi...