Sega Mega Drive/Hardware revisions

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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 VRAM 120 ns) 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). An issue in the hardware causes the RAM memory to not completely initialize when the game starts, causing crashes in Osomatsu-kun Hachamecha Gekijou.
	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 315-5339 (DIP-16) VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: 2x HM53461ZP-12 (64Kx4 VRAM 120 ns) 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 VRAM) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145 FM synthesizer: Yamaha YM2612
	VA3 (USA, High Definition Graphics)
	Components: M68K CPU: Motorola MC68000P8 M68K memory: 2x HM65256BL-10 (32Kx8 PSRAM, 100 ns) Z80 CPU: Zilog Z0840004PSC Z80 memory: KM6264BL-10 (8Kx8 SRAM, 100 ns) I/O chips: Sega 315-5308, Sega 315-5309 VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: KM424C64Z-10, VKF015 (64Kx4 VRAM) Headphone amp: Sony CXA1034 Video encoder: Sony CXA1145 FM synthesizer: Yamaha YM2612 Capacitors : Taicon, Chhsi
	VA4 (JPN)
	Components: M68K CPU: Signetics SCN68000C8N64 M68K memory: 2x TC51832SP-12 Z80 CPU: Zilog Z0840004PSC Z80 memory: NEC D4168C-15-SG I/O chips: Sega 315-5364, Sega 315-5309 VDP: Sega 315-5313 (Yamaha YM7101) Headphone amp: Sony CXA1034P Video encoder: Sony CXA1145P FM synthesizer: Yamaha YM2612
	VA4 (PAL)
	Components: M68K CPU: Motorola MC68000P8 M68K memory: Hitachi HM65256BLSP-10 (32Kx8 PSRAM, 100 ns) I/O chip: Sega 315-5364, Sega 315-5309 Z80 CPU: Zilog Z0840004PSC Z80 memory: Sanyo LC3664RL (8Kx8 SRAM, 120 ns) VDP: Sega 315-5313 (Yamaha YM7101) Video RAM: Fujitsu MB81461-12 (64Kx4 VRAM) Headphone amp: Sony CXA1034P Video encoder: Sony CXA1145P RGB Encoder FM synthesizer: Yamaha YM2612 Dual Operational Amplifier: Ti LM358P
	VA5 (JPN)
	VA6 (JPN)
	The first Japanese revision with the TMSS.
	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
	VA6.5 (PAL)
	The unused female DE-9 port (used for the Mega Modem in Japan) is removed.
	VA6.8
	VA7 (USA)
	Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: 2x 65256BLFP-10T Z80 CPU: Zilog Z0840004PSC Main ASIC: Sega 315-5487-01 Headphone amp: BA10324AF Video encoder: Sony CXA1145M FM synthesizer: Yamaha YM2612 (ASIC YM3438) A function on the VDP has broken PAL 50Hz support.

Model 2

	VA0 (JPN)
	VA0 (PAL)
	VA0 (USA)
	Components: M68K CPU: Hitachi HD68HC000CP8 M68K memory: Toshiba TC51832AFL-10 Z80 CPU: Toshiba 84C00AU-6 Main ASIC: Sega 315-5487-01 Video Encoder: Samsung KA2195D Amplifier: Texas Instruments 311223J
	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)
	PCB Printed by SKS Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: Sanyo LC36648ML-10 Z80 CPU: Toshiba 84C00AU-6 Main ASIC: Sega 315-5660-02 Video Encoder: Samsung KA2195D Amplifier: BA10324AF
	VA1.8 (USA)
	PCB Printed by CMK Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: Sanyo LC331632M-12 Z80 CPU: Zilog Z84C0006FEC Main ASIC: Sega 315-5660 Video Encoder: Samsung KA2195D Amplifier: BA10324AF
	VA1.8 (PAL)
	Components: M68K CPU: Motorola MC68HC000FN8 M68K memory: ??? 651632DFP-15 Z80 CPU: Zilog Z84C0006FEC Main ASIC: Sega 315-5660 Video Encoder: Fujitsu MB3514 Amplifier: BA10324AF
	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 Amplifier: BA10324AF
	VA2 (USA)
	Components: M68K CPU: Motorola MC68HC000FN12 M68K memory: Sanyo LC331632M-12 Z80 CPU: Zilog Z84C0006FEC Main ASIC: Sega 315-5786 Amplifier: Sega 315-5684 FM synthesizer: Yamaha YM2612 This revision (and the VA2.3) is the only Model 2 boards with a discrete YM2612 chip. Additional circuitry is present on the daughterboard located on the PCB, with model number 171-6961A.
	VA2.3 (USA)
	Components: M68K CPU: Motorola MC68HC000FN12 M68K memory: Toshiba TC511632FL-10 (32Kx16 PSRAM, 100 ns) Z80 CPU: Zilog Z84C0006FEC Z80 memory: KM78128LG-7 (8Kx8 SRAM) Main ASIC: Sega 315-5685 Video Encoder: Sony CXA1645M Amplifier: Sega 315-5684 FM synthesizer: Yamaha YM2612 This revision (and the VA2) is the only Model 2 boards with a discrete YM2612 chip.
	VA3
	Components: M68K CPU: Motorola MC68HC000FN12 M68K memory: ??? 651632DFP-15 Z80 CPU: Zilog Z84C0006FEC Main ASIC: Sega 315-5660 Video Encoder: Sony CXA1645M Amplifier: Sega 315-5684
	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)
	Components: IC1: Sega 315-5960 ASIC (see above) IC2: Sharp LH5P1632N-15 32Kx16 PSRAM IC5: OKI M54C864-80 512K (64K x 8-bit) VRAM IC6: Sony CXA1645M RGB Encoder IC7: TI LM324 amplifier IC3 and IC4 markings are silkscreened but don't correspond to any physical ICs.
	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