Then by simply by unplugging and/or turning the system off/on some of the 2645's stopped working.
How are you turning the system on/off? If you are using the miniswitch under the patchbay (the one with the channel bay power switches), don't! The 250V contact is very likely welded closed. Just mentioning because I had a very small memory somewhere that this used to cause card failures - and nasty shocks.
Have you checked that you are getting 83V across D7? (Or at least somewhere between 75 and 85V.) I'd be surprised if that's a problem, the 85V regulator is more likely to fail altogether than to give too high voltage, but it's
just possible that it's giving a high voltage above, say, 85V. Please be careful while checking this!!!!
Personally I wouldn't expect the DIL packages to work, but someone here
may have made them work.
I did check my spares box because I thought I had some original 2645s from SSL I'd have happily sent you, but sadly not
I quite understand you wanting to chuck these and fit VU's, I know the feeling...the plasma technology was the best available at the time, but was always a bit agricultural. Very clever, particularly the storage part, but when LCDs came along they were always going to be way more reliable.
Let us know how you get on,
Good luck,
Andy