On the Rev F CPU board, the interrupt synchronization mod cuts out the pin 5-6 inverter
in IC12 and uses it to create INTA- from INTA+ for the mod. However, this inverter
is required to use the onboard/offboard feature that Polex uses. If your Rev F CPU
board has the interrupt mod, there is unused inverter at pins 13-12 in IC12 that
can be re-inserted to restore the onboard/offboard logic path:

  1) Connect a wire from IC12p12 to IC11p11

  2) Connect a wire from IC12p13 to the right feedthrough under C19 (viewed from the top),
     or if more convenient, the left feedthrough under the "C22" silkscreen word. Verify
     verify the feedthrough you choose connects to IC30p7.