I've recently installed a SewQuiet 5000 onto my Juki 1508N and was about to test out the new v-belt I installed for it and the machine "locked up".
Initially I thought it was the Safety Clutch, but it doesn't appear to be engaged. I removed the plates and even the presser foot cover and saw that the basket was rotating with the hook.
Here is a video of the problem that shows it in detail:
What could cause something like this to happen and how can I fix it?