Shamelessly stolen from BobDenford on Reddit.
I recapped my SE/30 but mistakenly reversed the polarity of the two axial capacitors (C2 and C11). Prior to my error, the machine was fully functional with the exception of being unable to produce sound. When I turned the computer on the first time after replacing the capacitors, the startup chime rang. The computer was on its side, so I didn't see whether the display worked. I turned the computer off, attached the floppy and hard drive, put it right side up, and powered it back on. The fans spun up but the computer otherwise did nothing, even after I reset it a few times and let it sit powered on for a couple of minutes, at which point I removed the motherboard, discovered my error, and replaced the two capacitors, the larger of which (C2) was bulging. After doing so, the computer still refused to produce any video or sound. I tried reseating all of the onboard components, removing all but two sticks of RAM, resetting the PRAM, and pressing both the debug and reset buttons on the side of the motherboard several times to no avail. The floppy drive does nothing, even when a disk is inserted, and my scsi2sd flashes a yellow light once upon powering the machine on, then remains inactive. There is no obvious physical damage to the board, aside from the now-replaced bulging capacitor, and there is no indication that any of the components are missing their magic smoke (that is to say, I never saw, smelled, or heard any).
A working motherboard inserted into the same machine produces a display (no sound, still have to recap that one).
Is the board irreversibly destroyed? If not, what is likely to be damaged and how can I repair it?