[Zeke]

IDk if you used water or the thing ate lots of dust. But 2 things could have happened, one is more likely. You overheated the armature (likely) or the brushes gave up.

I think cannibalizing one saw to fix another is a fool's errand. The real world prices for decent used 77's is south of a hundred bucks. That is where I'd go. Keep the old one for the gears, foot, switch, etc.

It's a sad world when the 77 is no longer the king.