Tempest Board Interesting Problem

Yes...Here's another Tempest board with a problem.  This is my spare board and I thought I'd try and get it working today.  Not sure what happened to it in its former life but it must have been bad.  Replaced 9 RAMs and was left with these symptoms
 
1) Board passes self test, and displays self test screens correctly with a stable picture.
 
2) When I switch to game mode, I get the correct text but the maze and character vectors are jumbled  and strangely sized, and the input overdrives the monitor enough to cause it to blank out every second or so.  Vectors are often huge and actually caused my monitor to blow it's fuses at one point. 
 
3) With monitor disconnected game appears to play fine with correct sounds etc. 
 
So far I have:
 
Used known working Aux board
Replaced the faulty RAM
Switched out the video and game ROMs with a known working set
Switched out the processor with a known good one
Switched out the interconnect cable with an known good one
Resoldered the header pins
 
I've seen boards that played blind, but never one that passed AND displayed the self test correctly and then was unable to display the game play.  I figure anything that killed of 9 RAM chips might have seriously messed with the remaining chips on the board.   Anyone have any ideas where to start?  -Malcolm
 
 
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Received on Fri Jan 2 01:42:08 2009