I’m happy to report that the attempt to refurbish the ADM-3A’s screen went absolutely beautifully!
After watching a series of informative videos on YouTube stepping through the process, I was pretty confident that it would be a fairly easy task.
I followed the gist of instructions laid out in the video, with the exception that I didn’t preheat the lens with a work light beforehand - the CRT was small enough that it proved easy to heat up using just the gun. I also used bamboo skewers to poke underneath the lens to coax out hunks of PVA as I went, which worked out nicely.
Once the lens was removed from the CRT, I used Goo Gone to clean up any remaining PVA, and Windex with newsprint to clean up streaks and fingerprints. I applied bits of double sided foam tape around the outside of the CRT to hold the lens and keep it elevated from the CRT face, and after fitting the lens in place, sealed with packing tape around the perimeter to guard against any foreign matter entering between the lens and CRT. I then reinstalled the CRT assembly and it looks as good as the day it was made - no signs of burn in and perfect image quality.
Now I can concentrate on the lower case ROM project; I have the EPROM burned and ready, just need to wire up the shim socket. Hopefully I can get that completed later this week.
Any luck on the lower case ROM? I have one of these, and wouldn't mind some lower caseness. Fortunately mine doesn't require fixing the screen. I do have a few keys that seem to bounce a little (double strikes) and the brightness knob is a bit temperamental.
No, I wasn't able to get the homebuilt lower case ROM to display anything that wasn't Klingon. I did get a second ADM-3A with a lowercase ROM and swapped between the two units successfully, so there's something wrong with my build and not the ADM-3A itself (or the added character RAM chips). It would be nice to find a proper wiring diagram someplace - apparently my guesswork isn't sound enough :(