the chain on my ms 1640 mccullough electric chain saw
came off; after fixing the problem, I tried to restart it, but no dice. Do these units have a reset button?

JULES WEISS, February 2010

There is no re set button as such, however there is an actuating lever connected to the chainbrake handle, pull the handle fully back, this should set the internal lever, the lever ios p[lastic so if it has bent or deformed you will have to remove the motor cover and inspect/replace.

Husqvarna man, February 2010