I recently plugged in an old Apple IIGS that had been sitting in a basement for almost 15 years and it worked for awhile before blowing up in a smokey mess. The reason for the smoke was easy to diagnose, one of the line filtering film capacitors had exploded and shattered. The fuse was also blown in the process (so I'm assuming the capacitor managed to somehow blow in a short-circuit fashion).
Although it is straightforward for me to buy replacement parts and repair the device, is there a particular reason why a film capacitor would fail in such a spectacular fashion? My understanding is that typical film capacitor failure modes involve a gradual reduction in capacitance, rather than a sudden internal short circuit. Does a capacitor failure in this fashion typically indicate another component has also failed down the circuit? Unfortunately, I do not have schematics for the power supply, but my understanding is that "Type X2" capacitors are "across the line" — between line and neutral. The exploded (and also the intact capacitor on the other side of the transformer) read: 0.22uF X2 and have a 250V rating.
Best Answer
Going by the colour of the capacitors, they look like Rifa PME 271M types. If that is the case, they are well-known in vintage computer circles. The BBC Micro PSU was fitted with them (made 1981 or so) and they fail with a lot of smoke but no fire. The smell is characteristic, a sort of wood-smoke, bonfire smoke smell. The standard fix for the BBC Micro (and similar Acorn PSUs) is to replace them all with modern X-class equivalents.
In this forum post:
http://www.vintage-radio.net/forum/showthread.php?t=69128
There's some failure analysis, which suggests a mismatch between the capacitor itself and the epoxy coating. Rifa capacitors that have not yet failed usually have many tiny hairline cracks in the epoxy outer shell.
Do an image search for "Rifa PME271M" to see more examples of failed capacitors.