Uploaded July 2019 | Updated September 2026, 1 week ago

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Keyboard replacement can also be found here:
youtube.com/watch?v=0aqKDdpYr4c

For your reference:
NPN – 2N3904 or BC547 or BC548.
RAMTop values: 1K = 17408, 2K = 18432, 16K = 32768.
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MODEL ZX81
MANUFACTURER Sinclair
TYPE Home Computer
ORIGIN United Kingdom
YEAR march 1981
BUILT IN LANGUAGE Sinclair Basic
KEYBOARD Touch-sensitive keyboard, 40 keys
CPU Zilog Z80A
SPEED 3.5 MHz
RAM 1 KB (901 bytes available, up to 64 KB)
ROM 8 KB
TEXT MODES 32 x 24 (but 2 lines are reserved for system messages and commands)
GRAPHIC MODES 64 x 44
COLORS Black & white
SOUND No
SIZE / WEIGHT 167 x 175 x 40 mm / 350gr
I/O PORTS Z80 Bus, tape, video