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Sega Model 3

The peak of Sega arcade 3D (1996): PowerPC + Real3D graphics (Lockheed Martin, derived from military simulators), far ahead of its time. Virtua Fighter 3, Scud Race, Daytona USA 2, Sega Rally 2, Virtua Striker 2… In Steps (1.0 → 2.1).

A complete Model 3 board, its ROM banks in a row.
A complete Model 3 board, its ROM banks in a row. Photo uploaded by Mikel to Sega Retro, a site under CC BY 4.0.

Identification

Field Value
Manufacturer Sega
Year 1996
Type High-end 3D platform (multi-PCB)
Revisions Step 1.0 / 1.5 / 2.0 / 2.1
I/O dedicated harness (Step 1.x) → JVS on some Step 2.x

Architecture

Block Chip Clock Role
CPU IBM PowerPC 603/603e 66 MHz (Step 1.0) → 100 MHz (Step 2.x) game logic
Graphics Real3D Pro-1000 (Lockheed Martin) textured polygons + Gouraud/specular, trilinear filtering, fog, lighting — derived from the military Real3D/100
Sound Motorola 68000 + 2× SCSP (Yamaha) + Digital Sound Board (DSB): 68000 + MPEG decoder for streamed music
Tilegen / 2D Sega customs 2D planes + interface, protection

The Real3D Pro-1000 comes straight from military flight simulators (General Electric/Lockheed): it handles textures, Gouraud shading, specular highlights, fog and trilinear filtering at a level unheard of in the arcade in 1996 (well beyond the consoles of the era).

Steps (revisions)

Step CPU Sound / I/O Games (examples)
1.0 / 1.5 PPC 66 MHz SCSP (+DSB), dedicated I/O Virtua Fighter 3, Scud Race / Sega Super GT, Le Mans 24
2.0 / 2.1 PPC 100 MHz richer 3D, JVS on some Daytona USA 2, Sega Rally 2, Virtua Striker 2, Star Wars Trilogy, Spikeout

Costly and rare boards, multi-PCB (CPU, Real3D video, sound); the Real3D customs are irreplaceable.

Notable games

Virtua Fighter 3 (1996), Scud Race / Sega Super GT, Le Mans 24, Daytona USA 2, Sega Rally 2, Virtua Striker 2, Lost World: Jurassic Park, Star Wars Trilogy Arcade, Spikeout, Dirt Devils, Harley-Davidson & L.A. Riders.

Security & preservation

  • Protection: the Model 3 has security mechanisms (tilegen/crypt, encrypted data on some games) — hence emulation took a while.
  • Emulation: the reference is Supermodel (a dedicated Model 3 emulator), which runs most of the catalogue; MAME support is partial. No FPGA/MiSTer core (PowerPC + Real3D far beyond the DE10-Nano).
  • Maintenance: complex multi-PCB boards → methodical diagnosis; targeted recap, rare RAM/customs. 31 kHz monitor common (see CRT repair).

Common faults

Symptom Likely cause Lead
No image / corrupt 3D Real3D (Pro-1000), PowerPC, video RAM Board-by-board diagnosis; Real3D customs irreplaceable
No streamed music DSB board (68000 + MPEG) DSB diagnosis
Partial sound 2× SCSP Sound-stage diagnosis
Freeze / reboot RAM, multi-board power, heat Reseat, RAM test, recap, ventilation
"Security" / tilegen protection (encrypted data) MAME/Supermodel document it; custom diagnosis

Complex multi-PCB boards (CPU / Real3D / sound) → methodical diagnosis. A 31 kHz monitor is common. Real3D customs (military-derived) are near-unobtainable → preservation via Supermodel is advised.

EPROM repair

PowerPC 603 program. Mask ROM ROM board + boot EPROM; security via the game's ROM board. Scud Race, Virtua Fighter 3, Daytona USA 2, Sega Rally 2. No classic program EPROM — repair = the whole ROM board.

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/model3.cpp — pixel clock ÷ htotal.)
  • FPGA / emulation: see the Emulation & FPGA section below.

Repair (technician)

  • Costly multi-PCB (PowerPC 603 + Real3D video + sound): diagnose block by block; Real3D customs are rare and expensive (donor), careful inter-board connectors.
  • ROMs sometimes encrypted per game → check the config before suspecting the logic.
  • Sound: 68000 + 2× SCSP + DSB (MPEG) for streamed music.
  • Capacitors: recap (old multi-PCB boards).

→ 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
M68000 11.2896 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.

Procedure — a dead board, step by step ✅

What this adds

The general method lives in PCB diagnosis. This is its application to this platform: the same order, but with the values actually expected here, so you do not have to go back and forth.

Tools: multimeter, oscilloscope (or frequency counter), current-limited bench supply, desoldering braid. → Tooling

If the board is still in a cabinet

A CRT holds its charge with the machine unplugged. → CRT safety

1. Inspection, power off. Corrosion, cut tracks, oxidised EPROM legs, leaking SMD capacitors, dubious earlier repairs.

2. The connector, before anything else. A large share of "dead boards" are a contact problem, not a fault. Clean the contacts with isopropyl alcohol and reseat — not with an abrasive eraser on a gold edge, which takes the plating off and brings the problem back worse. It costs two minutes and settles the question.

3. Power, measured on the board. Aim for +5.0 V measured as close as possible to where power reaches the board — not at the PSU output: the drop is in the loom, and that is exactly what makes a board boot on the bench and not in the cabinet. Where you probe depends on this board's connector — JAMMA edge, JVS loom or a proprietary harness — plenty of makers kept one long after JAMMA arrived — see Identification above. → Wiring Check −5 V and +12 V too if the sound stage uses them. Suspected short: bring it up current-limited and find the hot spot.

4. /RESET. It must release after power-up. Held low = the CPU never starts. A 1–2 Hz loop is not the reset circuit, it is the watchdog: the CPU is crashing at boot, so look at the bus, not at the reset.

5. Clocks — the values expected on this platform.

  • M68000 → 11.2896 MHz (Main CPU)

No clock on the M68000 (11.2896 MHz) and there is no point measuring anything else: the fault is the crystal, the divider, or the chip itself. That single measurement splits a dead board in two.

6. Bus. Activity on the main CPU's address lines tells you whether it is running or frozen. Frozen with good clocks and good reset → work RAM, bus buffers, ROMs.

7. It boots but the picture or the sound is wrong — that is another job: see Common faults on this page, then signal tracing.

Photos / assets

(To add: Model 3 set, PowerPC, Real3D board, DSB.)

Sources & attribution

  • Wikipedia — Sega Model 3 (PowerPC 603, Real3D Pro-1000, Steps 1.0-2.1, SCSP+DSB, games) — CC-BY-SA — https://en.wikipedia.org/wiki/Sega_Model_3
  • Supermodel — reference Model 3 emulator (hardware documentation)
  • System16 — Sega Model 3 Hardware — to reference
  • Internal page: Sega Model 2 (previous generation)

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.