I'm currently moving, the other day I pulled out my first DSO from under the desk where it had been collecting dust for a few years, thought that it was of considerable volume and hadn't been used for too long.
So I decided it was time to try to sell it, when I powered it up to take some photos it let some thick grey smoke out of the back. (Looks like the scope doesn't want to leave me...)
I opened it expecting to find a cracked RIFA line filter but there was none. The PSU is a real PITA to disassemble, the culprit was found fast enough: A shorted tantalum drop on the secondary.
It took more time to clean the burns than actually troubleshoot/repair. While in there, I made the most of it to clean some connectors and refresh some weak solders, that had signs of heating.
Note that the under-side has plenty of clearance between primary and secondary traces, but on the top side clearance is much reduced, the bad tantalum (secondary) melted through the plastic sheath of the primary bulk capacitor it was next to.