AP300DLX Stuck in "Inactive"

[waterman46]

After using the Robertson AP300DLX for many years it finally has developed a strange problem which locked the rudder at hard starboard (and almost led to grounding my vessel up against a rock seawall). I'll spare those details. But now the control unit (AP300DLX) upon turn on shows quickly "STBY" then "Inactive" and none of the keys will let me go beyond that. I want to try a Master Reset, but this requires going to the menu and I can't get there since the unit keeps displaying "Inactive" after every keypress.

I checked out the cable connecting the control unit to the junction box and electrically it is fine.

There is actually a feature of Roberson AP where, if you have more than one control unit, the ones that are not in use will show this same "Inactive". In my case I only have the one control unit, at the helm so it shouldn't display this.

My options, as I understand it, are to replace this unit with another used one or to replace both control unit and junction box with updated new models. Before I do that, I'd like to know if there is anything I can do to attempt repair or further debugging.

Doug