Looks like the problem with machine is on the CPU board. Top left of this image, RAM5101 at IC19.
40 Pin connector between the CPU and driver board also appears to be bad.
New Ram chip has been ordered and soldering new connectors now, will see if this gets the game out of diagnosis mode and into attract mode.
Pin Repair website is a great resource for those troubleshooting one of these older System 7 machines http://www.pinrepair.com/sys37/index.htm