Earlier quoted context omitted.
I recently fired up an old Mac Plus that has stayed in the family and everything seemed to work fine until it started smoking, the display started to go wonky, and then it quit... Almost certainly an old-capacitor issue
That sounds like the RIFA brand AC line filter capacitor blowing. Cheap and easy fix provided you have a soldering iron and the long Torx driver to get at the screws in the handle. :)
There is a lot of nostalgia invested in that thing, it was my family's first computer and my own personal first experiences gaming and programming.