Wanted to report on how this turned out but I can't.  Loco sat on the shelf for a few days, I had finally decided to dig into it, thought I'd give it one more test and it worked fine.  Could be a loose wire somewhere, if it happens again I do have the info sent.   

Thanks, great info.  Yes, absolutely dead, nothing working at all, move, sound, light.  "It's not dead, it's sleeping"  Monty Python. 

Hi,
Bought a Thunder Chief HO set with F7-A DCC sound loco in January, been running fine, not a lot of hours.  All NS EZ track.  Today just quit, nothing works.  2 other locos on same layout running fine.  I've never looked at one of these.  Any ideas?  Thanks.

Got it, thanks for the hints.  New EMD GP40 with sound.  Remove 2 screws that hold the black plastic cover on the speaker and gently pry the cover off.  There are 2 screws in the metal speaker housing that hold the body on the chassis.  Took me a few days to muster the courage, but was easier than I thought. 

Hi,
Absolute rookie.  How to change body shell on EMD GP40?