Re: Ah, memories.
I remember my first hardware mod. My ZX81 and speccy would crash when my mum switched on the hoover due to poor power surge protection in the PSU. Fitting a VDR inside the plug socket fixed it and everyone at school wanted it done. Fixed the school ZX80 and other IT tasks and was awarded a BBC cassette player which anything would load from it. Used it to broadcast games over CB radio for my mates to load.