Old stuff ...
My completed in 1978 Heath H11A still works. Two 8 inch floppy drives, but no hard drive. Like the above poster, I laid out the traces & boiled all the boards ... Mom was really pissed off at the mess in her kitchen, even though I cleaned it up when I was done ...
Does my Sun1/100 (pre-Orange logo) with four CDC Lark 9455 drives count as a Personal Computer? Mine is dated late 1982 ... It was scrapped and given to me by a Sun field service rep in 1989 or thereabouts, and even then it was old fashioned & kinda klunky. It still boots, and I just compiled "Hello, world." on it, so I guess it still works :-)
I have an IBM 1405 Disk Storage Unit dated 1963 that still worked when I plastic-wrapped it and packed it and misc. other bits & bobs (1402, 1403, cabling, documentation, some card decks, etc.) into shipping crates nearly 35 years ago. They are awaiting the completion of my 1401 restoration project ... IBM wouldn't let me have the 1401 back then, but were happy to allow me to cart away the "obsolete" peripherals. It took me almost 30 years to find a suitable dated 1401 to complete my set. Hopefully the stuff still works. It's technically a "small business system", not a personal computer, but it only had a single user/operator, so if you squint it could be considered a PC ...
I have various other functional old computers down in the museum/mausoleum, but none of them could have been considered "personal computers". Why? Why not :-) Some people collect stamps, I collect and restore obsolete computers.