Dewalt DCS570 7 1/4” 20 volt cordless circular saw. I was cutting 3/16” panels and after a few cuts the blade quit turning yet the motor still works fine. I pulled the blade off and everything looked in order but when I put the blade back on I noticed I could easily turn the blade by hand. It didn’t spin smoothly but sounded like a stripped gear would sound. I hoping to get some hints as to what to look for and where, before I open the case. The blade lock works and the motor runs and sounds fine.
I believe you will find that the Dewalt DCS570 is not a direct-drive from the motor but has a reduction gear. It sounds as though that gear drive has failed somehow.
If this is under warranty, contact Dewalt. If not, then it may be serviceable. It looks like parts for this model are available from Dewalt.