[Elecraft] KPA100 not communicating

[pjhend@ameritech.net]

Hit a little wrinkle tonight while working on the KPA100: reached the
point where I hooked up the ribbon cable between the K2 and KPA100
board. I suspected something was amiss when the "NO PA PS"
message did not pop up in the display following the "ELECRAFT" message.
When I tapped MENU & then DISPLAY and rotated the VFO knob to PA, the K2
dispayed  "PA  --", indicating that the microcontroller is not
communicating with the K2. All voltages were fine on U1, U2, U4, U5, &
U6, the ribbon appears fine, and the microcontroller is not installed
backwards. any suggestions or ideas of where else to look?
Thanks!
Paul        kb9yvp