Sega Mega Drive/Hardware revisions

Model 1

	VA0 (JPN)
	Components: M68K CPU: Signetics SCN68000C8N64 M68K memory: 2x HM65256BLSP-15 (32Kx8 PSRAM, 150 ns) Z80 CPU: Zilog Z0840004PSC Z80 memory: TMM2063P - 10 (8Kx8 SRAM, 100 ns) I/O chips: Sega 315-5308, Sega 315-5309, Signectic 74LS00N, 74LS161AN, 74F161AN, 74LS74AN (DIP-16) VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: 2x HM53461ZP-12 (64Kx4 DRAM 120ns) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145 FM synthesizer: Yamaha YM2612 Due to a last-minute issue with the VDP in H40 mode, additional clock circuitry had to be added during manufacturing. This circuitry is present on a daughterboard in the center of the PCB, and contains the master oscillator (53.6931 MHz, NTSC), a 74LS74 (dual D-type flip-flops), and two 74LS161s (4-bit counter).
	VA1 (JPN)
	Components: M68K CPU: Signetics SCN68000C8N64 M68K memory: 2x TC51832SPL-10 (32Kx8 PSRAM, 100 ns) Z80 CPU: Zilog Z0840004PSC Z80 memory: NEC D4168C-20 (8Kx8 XRAM, 200 ns) I/O chips: Sega 315-5308, Sega 315-5309, Sega 315-5345 (DIP-16) VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: 2x HM53461ZP-12 (64Kx4 DRAM 120ns) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145 FM synthesizer: Yamaha YM2612 Capacitors : TK Japan
	VA2 (USA, High Definition Graphics)
	Components: M68K CPU: Signetics SCN68000C8N64 M68K memory: 2x TC51832SPL-12 (32Kx8 PSRAM, 120 ns) Z80 CPU: Zilog Z0840004PSC Z80 memory: NEC D4168C-15 (8Kx8 XRAM, 150 ns) I/O chips: Sega 315-5308, Sega 315-5309, Sega 315-5345 (DIP-16) VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: 2x [NUMBER PLEASE] (64Kx4 DRAM) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145 FM synthesizer: Yamaha YM2612
	VA3
	VA4 (PAL)
	VA5 (JPN)
	VA6 (JPN)
	VA6 (USA, High Definition Graphics)
	Components: M68K CPU: Motorola MC68000P8 M68K memory: 2x HM652568LSP-10 (32Kx8 PSRAM, 100 ns) Z80 CPU: Zilog Z0840004PSC Z80 memory: MB8464A-10 (8Kx8 SRAM, 100 ns) I/O chip: Sega 315-5433 VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: 2x [NUMBER PLEASE] (64Kx4 DRAM) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145P FM synthesizer: Yamaha YM2612
	VA6 (PAL)
	VA6.8
	VA7 (USA)

Model 2

	VA0 (PAL)
	VA1 (USA)
	VA1 (PAL)
	Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: Sanyo LC331632M-12 Z80 CPU: Toshiba 84C00AU-6 Main ASIC: Sega 315-5660 Video Encoder: Fujitsu MB3514 Amplifier: BA10324AF
	VA1.8 (USA)
	VA1.8 (PAL)
	VA1.8 (Asia)
	Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: Toshiba TC511632FL-10 (32Kx16 PSRAM, 100 ns) Z80 CPU: Toshiba 84C00AU-6 Z80 memory: [NUMBER PLEASE] (8Kx8 SRAM) Main ASIC: Sega 315-5660
	VA2 (USA)
	VA2.3 (USA)
	VA3
	VA4
	Components: IC1: Sega 315-5960 ASIC IC2: 32Kx16 PSRAM IC3: Video RAM? IC4: Sega 315-5684 audio amplifier IC5: Sony CXA1645M video encoder IC6: 7805 voltage regulator This is the first Mega Drive board without any discrete CPUs. Both the 68000 and Z80 are contained with the Sega 315-5960 ASIC, as well as the VDP, YM2612, and I/O controllers.

Model 3

	VA1 (USA)
	VA2 (USA)
	Components: Main ASIC: Sega 315-6123 (contains M68K, Z80, VDP, YM2612, and probably some other components.) Memory (right of main ASIC): NEC D4502161G5 (128Kx16 SDRAM) Oscillator (bottom-right of main ASIC): SG53 PTR S 53.6931M Video Encoder (bottom-left of main ASIC): Sony CXA1645M Amplifier (left of main ASIC): TI 85AFTRF LM324