Safety critical RF remote control protocol?
 

Coupled remote control with main unit. Both ends are transmit and receive
using Nordic semiconductor nRF905 tx/rx chip sets.
The synchro routine seems to work , requiring 2 way link both ways, to
synchronous codings between both units. But whatever button is pressed ,
opens up the serial data line on the main unit , but non varying with
whatever button is pushed.
Uses Atmel ATMEGA68 uC on the hand unit and 2 x ATMEGA168 on the main unit .
One probably for synchro and decoding functions and the other for opening
out/monitoring to/from the controlled operations. Otherwise uses 4066 and
ULN2003A to buffer out to relays and powerfets for pulsing/speed control. So
pinouts available for all ICs involved
Is the failure likely in the decoding / fanning-out operation or some
feedback monitoring signal not getting to the main unit Tx as
confirmation/handshaking?
How to narrow down to which, no schematic available, and thick conformal
coating over SM does not help