The power supply has 12V 2A. Nothing is connected in the Vin - GND connectors, as shown in the photo. The engine runs sometimes when I activate EKOS, then turns a few times and stops. If I click the focuser arrows, nothing moves. If I turn Ekos off and on again, the stepper start. When I log out of Ekos it stays yellow.
The stepper is same as you have and is 10V 0.4A; can you tell me how you configured it in Indi?
 
 

The stepper running when INDI starts may just be the focuser park feature. You can disable it. Personally I've found it more annoying than useful.
I noticed you turned the POT up a few notches. If it works, great. You should also remove that foam pad.
The message in your image is saying it can not move below Zero. This is normal. At zero position there are 3 things you can do. You can take steps up from there. You can Sync the position to a higher value. And you can use the Reset Position to run the motor to a lower position, but will still show position zero afterwards.

Andrew:

Out of curiosity: What is your experience with cooling the Pi4 with that HAT in place? I find it imperative to keep the Pi4 cool. I am using this heatsink

smile.amazon.com/gp/product/B07PCMTZHF/r..._title?ie=UTF8&psc=1

and it works great, even in the Texas summer here, the CPU temperature never gets above 48 C. And that is with up to 38 C ambient!

But I can not use it with that HAT in place, unless I move the HAT much higher. In that case, I might as well put it into a separate case.

Or use the Moonlite-based MyFocuserPro instead, which is based on an Arduino and works flawlessly for me.

Just to update:
I received a new waveshare HAT today. It does in fact show a connection between pin nENBL and pinheader pin GPIO12, so my old board definitely seems to be faulty. Interestingly, the new board came in a different packaging and had no board revision on the back.
Connecting to my RPi4 showed no success at all,  the motor did not react in any way. On a RPI3 however the python demo code did work (only control code "softward"). I also could measure square waves on the coil output. The new board seems to be OK.

I conclude that also my RPi4 is bad. So I need to order a new RPi4 also. In this regard: do we have experience/information wether a RPi4 w/8GB is beneficial over a 4GB version?

Thanks for your support so far.

Waveshare HAT was bad, returned everything to amazon and buy this: www.amazon.it/gp/product/B01MRJR8UF/ref=...01_s01?ie=UTF8&psc=1
www.amazon.it/gp/product/B01IP7IOGQ/ref=...01_s00?ie=UTF8&psc=1
Thank for all.
Ettore
 

@El Carozon:
I made a quick and dirty housing using a material similar to acrylic glas (better mechanical properties) and added a fan to its side, see attached picture. This seems to keep both boards fairly  cool.
 
 

Oops, added the picture twice ...

@Astrofilo66
It seems that this board is an Arduino UNO rather that a wave share HAT ...

Yes.
 

Wow, interesting. Maybe the defective HAT damaged the Pi. Either way, I'm glad the new HAT seems to be working better.

4GB has been plenty for running KStars and PHD2 (I don't run anything else). I don't normally run PHD2, just wanted to state that it could run both.

The only time I run out of memory is when doing a build and using the -j option to run many build processes in parallel. But otherwise 4GB seems plenty (for me).
 

Have you given up on the Waveshare?  That Arduino can't drive a focuser without a separate DRV8825 board.

Yes, I gave up and took Arduino with A9888 driver and www.amazon.it/gp/product/B01IP7IOGQ/ref=...01_s00?ie=UTF8&psc=1
Ettore