Thanks for the reply.
This is not a new install.
I flew with B/U battery disconnected for a while now, and decided to try again and connect it. I faced the same issue.
After your information- I tried again to connect, the b/u battery.
The voltage is 13.0 without the B/U battery, and 13.1 the voltage of the B/U,
The screen came on this time, as it should so I am puzzled.
I will try again, before the next flight, to connect the battery, and see how that goes.
Thanks anyhow, will keep following this issue.
David