These are tantalum caps, some call them "tantrum" caps. The reason is that they have the tendency to fail short, making a short circuit preventing the machine from starting, and sometimes even exploding.

You can't tell if they're dead by looking at them, however you can check if they're bad using an ohm metter. If the resistance is really low (0-40ohms I'd say, maybe even more), they're bad.

Tantalum capacitors from that era usually last a very long time, decades. I wouldn't worry about them. I would worry about tantalum capacitors in a 1980s IBM pc (tantalums on motherboard and floppy drive controller board often fail).

I've had a few 386 and 486 to explode on me before. Even 286 (from the 90's). The difference may be simply that they weren't old enough to die, not that they're really better

I have a theory (more like speculation really) that tantalums on "newer" boards like 386 and 486 explode due to voltage spikes, not because of aging. In particular I have noticed that most of the time it's the caps on the -12V line that pop, followed by the 12V ones. And it usually happens when they are rated up to 16V rather than, say, 25V. Failures on 5V/-5V lines are much less common in my experience, and those are usually rated at 10V or more.

So, the fact that the explosions seem more likely to occur either on lines that are poorly regulated (it is common to see the -12V being out of whack in older PSUs) or when there is a smaller safety margin in the rating of the capacitor (16V for -12V/12V) leads me to believe that voltage spikes might be the cause behind the explosions.

The tantalum issue on 80's IBM boards and expansion cards is way more frequent, so that is probably a completely different problem, more related to the manufacturing of the caps.

TheMobRules wrote on 2022-01-19, 17:06:

The tantalum issue on 80's IBM boards and expansion cards is way more frequent, so that is probably a completely different problem, more related to the manufacturing of the caps.

Idk I think it's the same thing. You never see the +-5V tants go on the IBM stuff - it's always the +-12V rails. And those caps are always 16V rated too

Ah, the good ole "Flying Spider" or "Tantrum" or Tantulum caps. My 286 has blown 3, I replaced them with Electrolytics, that thing has been rock-solid ever since I did that back the 00's. Honestly, other than that, I have not really had to re-cap very much computers. The worst was the motherboard for the EEC-IV PCM in my Ford Explorer that rotted some traces and turned one trace into a 12 ohm resistor (laughs). After doing that, I think I'm ready for anything.