this is exactly the problem.

It appears to be about 4 teeth shy.

How do I release the belt tension?

I have attached a photo of the right side with the left side against the pulley.

Remove the cover on the which ever side is off then loosen the two screws holding the bearing cub for the end of that rod. That will allow the rod to slide forward and allow you to move the belt by hand. It might be easier to adjust the left side though as the right side is the drive side and the motor makes it harder to move the belt on that side.

Just remember to confirm the adjustment with tension on the belt.

It appears to be about 4 teeth shy.

How do I release the belt tension?

I have attached a photo of the right side with the left side against the pulley.

everything looks clear.

The printhead moves freely in both directions  (by hand without power)

As soon as power is turned on, screens says "initializing" the head moves smoothly to the back right home potions...and tries to keep going. Belt slip noise, power off.

What can I do?

Thanks,

Bill

With power off bring your bring your x axis (left to right movement) full forward by hand. Look up in the top of the machine and make sure that it is bumping into the two white pullies on both sides. It sounds to me it is offset by a few teeth and the right side is hitting the back physical limit before the left side hits the home sensor. That tells me the right side is further back then the left. You will need to release the belt tension and move the belt over the the roller by hand a few teeth until both sides reach the white pullies at the same time.

The printhead moves freely in both directions  (by hand without power)

As soon as power is turned on, screens says "initializing" the head moves smoothly to the back right home potions...and tries to keep going. Belt slip noise, power off.

What can I do?

Thanks,

Bill