You could replace many ICs with just your fingers or a screwdriver. On the C64 the main ones like the CPU, graphics, sound and IO chips were in sockets, and that was similar on many home computers of the era.
I freaked my parents out by switching chips between our C64 and the floppy drive to see what would happen (they had almost compatible CPUs and IO chips - many things kept working).
Also: Repairing by touching chips to see if any of them were unusually hot was fun...
EDIT: to bring this more back to the thread subject, as a Commodore user at the time we used to make fun of the Spectrums, but they absolutely had a massive impact on the market. Including on competitors - e.g. Tramiel got spooked by how cheap the ZX81 was, and it certainly contributed to choices made at Commodore. Sinclair's influence as a result spread wide and far beyond the sizable direct influence of his own machines.
I freaked my parents out by switching chips between our C64 and the floppy drive to see what would happen (they had almost compatible CPUs and IO chips - many things kept working).
Also: Repairing by touching chips to see if any of them were unusually hot was fun...
EDIT: to bring this more back to the thread subject, as a Commodore user at the time we used to make fun of the Spectrums, but they absolutely had a massive impact on the market. Including on competitors - e.g. Tramiel got spooked by how cheap the ZX81 was, and it certainly contributed to choices made at Commodore. Sinclair's influence as a result spread wide and far beyond the sizable direct influence of his own machines.