FWIW, I'd add that the original GPS HC (1.2/1.6/2.2) can be flashed with NXS 4.22 (assuming that the AT49F040s are socketed), making it effectively a v4 hand control, with the caveat that it does not support firmware updates via HCupdate like a factory v4 HC. You lose the automatic GPS alignment but gain the GPS fix and compatibility with modern telescope control software via RS-232.
Thank you 12Bass. That was one of the "edge cases" I was specifically avoiding, but there is a valid argument to be made that if you have a scope with one of the older HCs and MC 1.0 /2.0 and if you get/have access to a PIC programmer, this extra info is imminently useful. So, I just added this to the article:
One final note - it is possible to load the latest version 4 firmware (NXS 4.22 as this time) on a version 1.2, 1.6 or 2.2 hand control by using a PIC programmer. If you need to update a version 1.0 or 2.0 motor control with a PIC programmer (see the next section) this could make sense. Otherwise, it is cheaper and much less complicated to purchase a version 4 hand control. Instructions for upgrading a 1.2/1.6/2.2 hand control with a PIC programmer are found in this discussion:
While all HC 1.2 have removable chips (easy to reprogram), as I recall most of the 1.6 HCs and all of the 2.2 HCs have surface mounted chips which I'm not sure you have tried to address in your topic linked above.
Other edge cases have more to do with dealing with a mount with several failed components. For example, the serial board is bad or the MC board is bad. We know it is possible to swap in a NexStar 5i/8i MC board if you first load MC version 4.06 with a PIC programmer (though it may also be necessary to reload it after that with MCupdate). I believe it would also be possible to bypass all other internal electronics (level switch, compass, GPS, serial board) and use all the internal electronics from a NexStar 5i/8i (again, after loading 4.06 on the MC board). This would provide the HC and AUX jacks for connecting external devices and return pretty much fully normal function to the mount.
So, I mention this here but since my NexStar 11 GPS lives on another continent at this time, I cannot experiment and this will have to wait to be added to my website until sometime in the future.
Edited by Michael_Swanson, 22 February 2020 - 04:50 AM.