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Sega Model 1

Sega's first major 3D platform (1992): real-time polygons that launched Virtua Racing then Virtua Fighter. Built on a 3D DSP (TGP) and a 68000. Rare and iconic.

Sega Model 1 board
Sega Model 1 CPU board (Virtua Fighter). Photo: htomari, Wikimedia Commons, public domain.

Identification

Field Value
Manufacturer Sega
Year 1992
Type Arcade 3D platform (flat/shaded polygons)
I/O JAMMA / dedicated harness

Architecture

Block Chip Clock Role
CPU Motorola 68000 ~10 MHz game logic
3D geometry Fujitsu TGP (MB86233, DSP) polygon transforms/projection
Graphics real-time polygon engine flat/Gouraud shading, no texture-mapping (solid colours)
Sound dedicated Motorola 68000 + Yamaha YM3438 + MultiPCM (315-5560) FM music + PCM samples

Sega's first "mainstream" 3D hardware (1992), by the AM2 team (Yu Suzuki). The TGP (Fujitsu MB86233) does all the geometry (transforming and projecting polygons), offloading the 68000.

The 'bare polygon' look (no texture)

The Model 1 does flat / Gouraud shading but no texture-mapping: faces are in solid colours. That's the visual signature of Virtua Fighter / Virtua Racing ("faceted" characters). The Model 2 (1993) precisely adds filtered textures — the next big leap.

Notable games

Virtua Racing (1992), Virtua Fighter (1993), Wing War, Star Wars Arcade (1993). A very small catalogue (a handful of titles) — the platform was quickly replaced by the Model 2.

  • Multi-cabinet: Virtua Racing could link up to 8 cabinets for multiplayer racing, a feat in 1992.
  • Home port: Virtua Racing was ported to the Mega Drive thanks to the SVP chip in the cartridge (see Mega Drive § Hardware quirks).

Preservation & emulation

  • Emulation: the Model 1 is emulated by MAME (reverse-engineered customs and TGP) — the preservation route, given the rarity of the hardware. No FPGA/MiSTer core (TGP + polygon engine too complex).
  • Rare boards: Fujitsu (TGP) customs and video ASIC hard to source → great care when repairing, mind the contacts and the power.
  • Targeted recap if image/sound degraded; dedicated monitor (see CRT repair).

Common faults

Symptom Likely cause Lead
No image / no 3D TGP (MB86233) or video ASIC, power Diagnosis; Fujitsu customs are irreplaceable → extreme care, mind the contacts
No / partial sound sound 68000 / MultiPCM (315-5560) / YM3438 Sound-stage diagnosis
Crash / unstable image RAM, interconnects, weak power Reseat, RAM test, targeted recap
Dead controls harness / dedicated I/O Check the wiring

A dedicated monitor (see CRT repair). The real risk is the rarity of the customs: favour software preservation (MAME) over risky teardown.

EPROM repair

68000 program (+ TGP). Ex. (MAME sega/model1.cpp): Virtua Fighter / Virtua Racing = 10× 27C040 + 2× 27C010 · Star Wars Arcade = 3× 27C040 · Wing War = 8× 27C040. Separate CPU / Memory / Raster boards; 3D data in mask ROM.

Modernisation & mods

The common ground for every JAMMA board

Video, power, control panel and upscalers depend on the cabinet rather than the board: everything is centralised in Modernising a cabinet. To run the board outside a cabinet (at home, on a display): supergun.

  • Storage 🟡: the game lives in EPROM/mask ROM on the board. Changing or restoring a game means reprogramming the EPROMs (and, for a mask ROM, using a pinout adapter) → EPROM method.
  • Media preservation: replacing the original storage, multicarts, ODEs and modern options by family → PCB preservation hub.
  • Scan rate 📺: ~24.39 kHz / 57.5 Hz — medium resolution, ⚠️ a 15 kHz-only chassis will not do: you need a medium-res monitor or a tri-sync → tri-sync and upscalers. (Computed from the MAME sources — sega/model1.cpp — pixel clock ÷ htotal.)
  • FPGA / emulation: see the Emulation & FPGA section below.

Repair (technician)

  • SVP cartridge (Virtua Racing): the geometry DSP is inside the cartridge — dead 3D = SVP/cartridge, not the CPU board.
  • Sega customs (video, MultiPCM 315-5560): rare → test RAM + buffers first, the custom last (donor).
  • Sound: dedicated 68000 + YM3438 + MultiPCM — silent samples = MultiPCM / sound ROM.
  • Capacitors: recap PSU + audio (a costly multi-PCB board → care, inter-board connectors).

→ Methods: PCB fault-finding · Recap · EPROM · Traces & vias

Expected clocks — measurement table ✅

Values extracted from the MAME sources for this platform. On a scope or frequency counter, a clock that is missing or off-value points straight at the crystal, the divider or the chip at fault — the fastest starting point on a dead board.

Component Expected clock Role
V60 16 MHz main CPU

How to read this table

Several values for one component = several board variants in this family (or several instances of the chip clocked differently). These frequencies are those of the clock signal at the component's input, not of its original crystal — on many boards the clock is divided down from a single master crystal.

Photos / assets

(To add: Model 1 board, TGP DSP.)

Sources & attribution

Image:

Review & corrections

How this space is used

Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.

Reading is open to everyone; posting requires signing in with Discord. Reports from the wiki's declared reviewers are handled first; anyone else's are read too, but go through a human before anything is changed.