You’re on the right track. It’s got a brush motor, so they may well be finished. These machines are also prone to burning out the tracks where the edge connectors join the board. Some also have a circuit protection fuse.
If you are not confident with using test equipment, you must get professional help.
Check the Directories section for a UKW engineer, or pop your postcode up in here and someone will pick up on it.
Whatever you do, pull the plug first.
Regards,
Penguin45.