My son was gifted three beautiful Williams F-7 Diesel locomotives.  We run basic Lionel trains (nothing fancy) and we do not have the knowledge about trains that most everyone on this board does.  Here's my question.  The F-7 locomotives run great, but will only run for a short period of time (maybe for 1 minute) and then stop.   We have to turn off the power and turn it back on to get it to start up again.  It's almost as if there is a time feature built in.  I'm not experienced to know if this is the case.  Can anyone provide troubleshooting tips (in lay terms) to help us figure out what may be causing this?  Thank you.