You can download the service manual from here
http://freeservicemanuals.info/en/se...sonic/NV780EM/
These type of panasonic/national mechanism (D1) when the VCR operates the mechanism proceed a <<selftest>> the capstan motor rotate the suplly reel table and the loading motor make a small movement (rotation). if the self test find a failure the VCR rotate for a few seconds the capstan or the loading motor (it depends from the failure) and then turn OFF.