Problems with focus

I’m seeing some issues related to focus. If I focus on the base plate, then move the focus up 10 mm, then down 10 mm, the base plate comes back into focus. But if I move the focus up say 30mm and then back down 30 mm, the base plate is no longer in focus at all, as in I have to search around to find it. Is this typical? I ask because we have some taller items that we are imaging, and have built a fixture so the height is always a set distance off the baseplate. We should be close to focus if we go to our known level, and sometimes this works. But sometimes it is far off of focus and we have to do a lot of searching.

One other thing is that normally the PC running the software makes a certain sound when something is plugged into a USB port,like the Profilm 3D or a mouse or USB drive. When we move the focus up and down,we often hear that same sound even though nothing is being plugged in or removed.

Any suggestions or experiences would be appreciated. Thanks.

A couple of other points possibly connected to this

  1. Sometimes when we power on we get a message that “An unexpected error occurred”.
  2. Sometimes when we power on we get a message “Failed to initialize video camera”.