U1
Zilog Z80
CPU
Main CPU
About this component
The Game Gear runs Master System-style software on a Z80A at about 3.58 MHz, with 8 KB of work RAM (NEC uPD4364G-15L). On VA0 the CPU is its own chip next to two Sega ASICs; on VA1 and later the CPU, video processor and SCA control logic are merged into one large custom chip, so a 'CPU fault' there means replacing the whole LSI. Most Game Gear faults are actually leaking capacitors and screen problems, which should be ruled out first. Part variants: Only the first VA0 board has a separate Z80A CPU. From VA1 onward the CPU core is inside the one-chip custom LSI (CPU + VDP + SCA, Sega 315-5535, 144-pin QFP).
What it does on this board
8-bit Z80 @3.58MHz.
Pinout & readings
No pinout or reference readings yet — these show what each pin does and what a healthy part should measure.