After replacing the RAM, the display is now back to normal (there's also a test switch on the motherboard (S6) that switches the display from blank spaces to all zeroes. The one that failed was a National Semi 2102, whereas the others are all (I once fixed up a PDP-8/L, chased down several bad chips. Nearly all were Signetics 7440's). I may have made a tactical error though - turns out that wet/damp PVA is electrically conductive! Enough to overcome the 5k pullup resistors. An unpleasant surprise. So now the keyboard thinks multiple keys are being pressed and won't work at all. Removing the keyboard to clean underneath it would be very tedious since every key has two soldered pins... There was a significant buildup of goop underneath the key scan mux and demux chips where the pins are close together (0.1"). I gave the bottom half of the board another good rinse and will let it dry overnight, maybe a hair dryer too. Or get some more 91% alcohol to it and a longer low-temp bake. It all worked before my "cleanup" so I expect it will resume normal operation once the moisture is out of any remaining goop. I hope ;) --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus