So an update and I wonder where this now leaves me:
I decided to update the firmware. Connected the Starsense HC on its own and went into BOOT LOADER mode. After a few turns around the houses to get the computer to see any serial port (my handset has the old style serial connector...) it saw the HC but not the mount. It updated the software for the HC. I then redid this with the Camera attached. This time the system did not see the attached camera, only the HC despite playing around with ports.
On switching on the AVX mount power after this procedure I was still getting the "err: Model Num" but now more quickly (after a couple of seconds!
I have access to my old Nexstar SE Mount and so I attached the Starsense HC and it works fine with this mount (but WHAT a pain to plug in the handset into the arm housing- had forgotten this nightmare of a design!!). I could now query the status of the HC software and I find it is now V 01.20.20265 Build Sept 22 2020 so must have updated when attached to the AVX mount, even though I could not query this when attached to that mount. So I guess the HC is fine. The camera version is V 01.02.13343 - I can't recall what the original version I had was. Is this a concern that I could not see my camera but just my HC?
I then decided to set up the CFM to update the Nexstar SE mount. The CFM finds the HC and now the SE mount but I could never get it to find the attached camera.
I next looked at the old Nexstar+ SE HC. It is the old style, No "Celestron" button and so I could not figure out how to send it into boot loader mode just to see if I could update this on either mount. On the SE the HC operates fine. Old software at 4.12. However when I plug THIS HC into the AVX I get an "error 16" message.
The original AVX HC (pre Starsense) remains dead on either the AVX or the Nexstar SE mounts.
So where to go from here? The Starsense handset seems fine. I would like to update the old Nexstar+ SE handset to see if this sheds any further light on the error but don't know the BOOT LOADER key. The AVX handset seems dead - took the back off but can't see any obvious reason for its inability to light up.
However the main conclusion seems to be that the AVX Mount does not want to play. Does this all mean the AVX Mount Control Board is dead? Should I attempt MCUpdate? I read that you cannot do this with the Starsense HC but would this be possible with my old Nexstar+ HC that seems to work in my old Nexstar SE mount (in which case do I need a BOOT LOADER command and if so what are the menu buttons that allow this?)
Edited by cpl43uk, 22 January 2021 - 06:18 PM.