It does sound like a proximity detector problem. The proximity detectors for the rotation are near the center hub toward the front side.

Here is a possible way to get in and wash off any chips. Connect a hose (garden hose) with a spray nozzle to the coolant pump (I hope you have the high volume pump). Haas used to supply washdown hoses and nozzles so you may have got one with the machine.

Now get a small screwdrive and slide back a pocket cover on the carousel disc; these arejust held closed by springs. Spray water into the carousel enclosure throught the open pocket, lots of water in all directions through different pockets.

If you still cannot get it to zero repeat the water spraying a few times; sometimes chips get glued on by coolant residue and will not wash off easily.

You may have success with this method, I have a couple of times, but if it doesn't work you go to the next step.

Look at the bottom center of the carousel plate and you will see a ring of 5/16" socket head cap screws. These hold the plate onto the hub and you can remove them to take the plate off. Be careful it is awkward and heavy and if there are tools in any pockets dangerous (I have the scars to rpove that).

Once you have the plate off you will be able to see the detectors inside the top near the hub.