All indications are that I have successfully revived one of my two GDM-5410 monitors. This is an OEM monitor made for Sun by Sony, sold by Sun as the Sun 21" FD (full deflection) monitor. It's a very nice CRT, having a truly flat (both vertically and horizontally) screen. Unfortunately, the entire monitor family seems to have a design flaw that causes the black level to progressively drift until black is ... well, sort of medium grey, and there are visible flyback lines across the screen, even with brightness turned down to 0 and contrast set to 100%.
Fortunately, there's a way to reprogram the EEPROM in the monitor. This page tells you all about how to do it, and how to get the cable and software you'll need. (The software requires Windows.) I got my cable here; it cost me about $27, shipped. You'll need a DB9M-F extension cable; the RS232 TTL cable is only about six inches long.
The one error I found on the page is that it says you can edit the downloaded EEPROM data file using Windows Notepad. You can't; you'll need a hex editor. I used this one, and it worked just fine.
The adjustment procedure shows a value of 84 for the G2 black level. Don't take that as gospel, because it apparently varies from model to model. Mine, when I started, was at 178. I dropped it in progressive steps down to 120, and at 120, I can set the monitor brightness back to 50% and still have dense, rich blacks. The SMPTE monitor test pattern now renders perfectly.
Upshot: $27 and about an hour of my time spent. Cost of one 21" replacement monitor saved. (Two, if I can similarly revive the other GDM-5410 that's upstairs in storage, which has the same problem, but possibly even worse than this one was.)
(One minor glitch: When I turned it on this morning, OSD lock was set and I couldn't clear it. I was able to solve the problem by just powering the monitor off, reattaching the diagnostic cable, powering it back on, reflashing the last set of register data, then powering off again and this time disconnecting vorlon's end of the diagnostic cable first.)
