ZX80

The cheap integer-only first Sinclair. No floating point, no sound, no graphics.

Open the ZX80 in Retro Bench

Also: Sinclair ZX80 (1980)
Year: 1980
CPU: Z80A (NEC 780-1) @ 3.25 MHz
RAM: 1 KB (2 x 2114)
ROM: 4 KB Integer BASIC
Video: Monochrome, 32 x 24 text, no graphics
Sound: None
OS: Sinclair BASIC (integer only)

Chips

Chip	Where	Role
Z80A CPU	IC1	Main CPU (8-bit, 40-DIP)
2114 SRAM 1K x 4	IC3, IC4	Static RAM (ZX80 and ZX81 1K)

Ports and connectors

Power in (9V DC IN), 3.5 mm mono jack
EAR (tape in), 3.5 mm mono jack
MIC (tape out), 3.5 mm mono jack
TV (UHF RF out), Phono socket (RF)
Rear edge connector (2 x 23), Card edge, 23 + 23 contacts, keyway at 3

Power rails

Rail	Expect	Measure at
+9 V DC in	9 V nominal, unregulated	Power jack; zx80-edge pin B2
+5 V	+5 V	7805 (IC22) output; Z80A pin 11; 2114 pin 18
GND	0 V	Z80A pin 29; 2114 pin 9; zx80-edge pins B4, B5

Symptoms

Gray mess on the TV, no K cursor
Will not start at all
Dead with the supply good: check Z80A, 2114
Locked up, BREAK does nothing
LOAD fails
Listing shrinks or vanishes as the program grows: check 2114