Thank you for your suggestions, Peter.
In this case Z assembly weights probably several hundred kilograms. And 
I don't have a big wish to remove the servo motor, although possible. 
Releasing the electromechanical brake makes it drop really fast.

By the way, I have never succeeded "setsing" or "setping" an encoder 
index-enable signal and waiting for it to go down by rotating the 
encoder by hand on other setups. I don't remember the exact behavior 
now. I thought it has something to do with less often used IO type of 
HAL pin.. But a bit of time passed, I should check that again.

What is interesting, while not proven, that encoder count (or rawcount) 
persists between different LinuxCNC sessions and resets only after 7i77 
5V power is re-applied. And exactly then I observe different Z position 
after homing.
These things are not easy to prove, as they require big number of 
different tries.

> I would hand check index detection by "setsing" the appropriate index-enable
> signal and turning the axis by hand and watching for the same index-enable
> signal to be cleared. If this does not work reliably it suggests you have a
> encoder index signal interface problem of some sort (wrong interface mode,
> too short index signal, missing index from resolver-digital converter, 5V
> problem on 7I77, cable issues etc)
> The encoder errors also suggest some kind of generic interface issue
> Another diagnostic would be to halscope the index pulse itself assuming you
> can move slowly enough to detect it in the servo thread, index pulses are
> often 1 encoder pitch wide (1/2048 in your case) so you would have to move
> more slowly than 2s seconds per turn to reliably detect it at a 1 KHz servo
> thread
> Peter Wallace
> Mesa Electronics
> ------------------------------------------------------------------------------
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