video problems: debugging help

[drstrip@gnome.cs.sandia.gov (David R. Strip)]

My dying 3645 refuses to send video to the terminal (or so it seems).
I have eliminated the following possibilities (usually by swapping parts
with a 3640 next to it):
   monitor
   monitor cable
   FEP board
   I/O board
   paddle card (is this the right name for the small card in the back
                that has the video output?)

The machine appears to be alive, since i get nice random patterns on the
monitor that disappear for a moment when I blindly type reset video.

What else can I pull/swap to try to isolate the problem?
Thanks
strip
drstrip@cs.sandia.gov  (don't trust the return address in the header.)