Atari Cojag¶
Area 51, Maximum Force, Fishin' Frenzy. Cojag is the Jaguar console turned into an arcade board — the one time Atari's hardware did better in arcades than at home. And it comes in two processor variants, which have to be told apart before any measurement.
Identification¶
| Field | Value |
|---|---|
| Manufacturer | Atari Games |
| Years | 1995-1996 |
| Base | Atari Jaguar — the same Tom and Jerry customs |
| CPU, variant 1 | IDT R3041 @ 20 MHz (40 MHz crystal ÷ 2) |
| CPU, variant 2 | MC68EC020 @ 25 MHz (50 MHz crystal ÷ 2) |
| Video crystal | 52 MHz |
| Timing | 456 × 262, 360 × 240 visible |
| PCB format | Atari proprietary |
Two different processors for one platform
This is the first reflex: look at which CPU is fitted. Some Cojags use an R3041 (MIPS R3000 family), others a 68EC020. The frequencies, the buses and the failure modes have nothing in common.
Expected clocks — measurement table ✅¶
| Component | Expected clock | Role |
|---|---|---|
| IDT R3041 | 20 MHz | Main CPU (MIPS variant) |
| MC68EC020 | 25 MHz | Main CPU (68k variant) |
The R3041's divider is not verified
MAME notes “divider not verified, but chip is rated for 20 MHz”. The 20 MHz figure is therefore consistent with the part, but its exact ratio to the 40 MHz crystal has not been confirmed. A slight discrepancy proves nothing.
What the Jaguar kinship changes¶
The graphics and sound core comes from the Jaguar console: the Tom and Jerry customs. In practice, for a technician:
- the console's graphics failure modes apply;
- community documentation on the Jaguar is partly transferable;
- but the main CPU is not the console's — the home Jaguar uses a 68000, the Cojag an R3041 or a 68EC020.
→ See the console page: Atari Jaguar.
Notable games¶
Area 51 (1995-1996, several revisions) · Maximum Force · Fishin' Frenzy · Freeze (1996).
The success the console never had
The Jaguar was a commercial failure at home. In arcades, Area 51 was a real hit — enough to be ported afterwards to rival consoles. The same silicon, two fates.
Common faults¶
| Symptom | Probable cause | Next step |
|---|---|---|
| No picture | CPU, the 52 MHz video crystal, or the Tom/Jerry customs | Establish which CPU variant is fitted first |
| Erratic behaviour | R3041 or 68EC020, board depending | Two platforms in one: do not compare measurements across variants |
| Corrupt graphics | Tom custom (Jaguar) | No replacement — diagnose by comparison |
| No sound | Jerry custom (Jaguar) | Same remark |
Repair (technician)¶
- Determine the variant before measuring. R3041 at 20 MHz or 68EC020 at 25 MHz: a value that is right on one is wrong on the other.
- The Tom and Jerry customs have no replacement, but they are shared with the Jaguar console — a dead console can serve as a donor, which is rare and valuable on an arcade platform.
- This is not JAMMA: Atari proprietary wiring.
→ Methods: PCB diagnosis · Recap
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.
- IDT R3041 → 20 MHz (CPU principal (variante MIPS))
- MC68EC020 → 25 MHz (CPU principal (variante 68k))
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.
Modernisation & mods¶
- No suicide: no battery-backed protection documented.
- ⚠️ Do not host ROMs — method only.
Emulation & FPGA¶
MAME covers the platform inside the Jaguar driver (atari/jaguar.cpp), which
handles the console and the arcade boards together — reflecting exactly their
hardware kinship.
Photos / assets¶
(To take: both CPU variants if possible, the Tom and Jerry customs, and the 52 MHz crystal.)
Sources & attribution¶
Text (synthesised here; sources listed for attribution):
- MAME —
src/mame/atari/jaguar.cpp(BSD-3-Clause / GPL): theCOJAG_CLOCK(52 MHz),R3000_CLOCK(40 MHz) andM68K_CLOCK(50 MHz) constants; the R3041 at 40 ÷ 2 with the note “divider not verified, but chip is rated for 20 MHz”, and the MC68EC020 at 50 ÷ 2 variant; the 456 × 262 (360 × 240 visible) timing; and the fact that the Jaguar console and the Cojag boards share the same driver, and therefore the same customs — https://github.com/mamedev/mame/blob/master/src/mame/atari/jaguar.cpp
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.