I've written to support, but I figures that I'd also post the trouble here for others to peruse.
I've finished the KX1 and KXAT1 and thought things were going ok, but several days ago, I turned on the unit and heard no relay, or only a single relay and a blank display. This would continue until I switched it off, or rotated the VFO knob, then several other relays would sound and the display would come alive. It almost seem that the VFO has to wake up the ATU MCU and only then would the KX1 MCU begin it's display.
Last night I attempted to find the problem and took out the KXAT1 and replaced the wire bridge...instant turn-on and display. So, I figure that the issue lay in 1) KX1 MCU to KXAT1 MCU communication or 2) some fault in the solder on the ATU. I went over almost every solder joint on the ATU board, removed and reseated the MCU (no bent pins), but still the trouble continues.
Tonight I will replace the ATU board and work through the sequence of relays. I'll also check the connector pins from the KX1 and re-solder them.
If there are any other ideas, I'd live to hear them.