As for oldest, I've messed with some old tube-type record players, ones that were made before the transistor was invented, and thus take a while to warm up. Also fixed a cassette recorder from the 60s, when "Made in Japan" was like "Made in China". Except for this thing was obviously assembled by hand and had the components soldered in by hand.
Intricateness is a pain, as it's hard to find the problem. I tried to figure out what was wrong with a neighbor's pinball machine, and even though it was a relatively modern one, it still had lots of moving parts and coils. Plus, you would be surprised about how complex floppy drives are, especially early ones.
The Microwave/Oven I have here are pretty awful. Seriously it can't do any number asides from numerals of 30? Fuck.
I'm pretty sure I've once opened a radio from the 30s or 40s.
I've seen a TV from the 50s before. Other than that, nothing I can remember.