Jaleco Mega System 32¶
Jaleco's top of the range in the mid-nineties, built on an unexpected processor: the NEC V70, the same 32-bit part as Sega's Multi 32. A platform where one clock in two remains uncertain.
Identification¶
| Field | Value |
|---|---|
| Manufacturer | Jaleco |
| Years | 1994-1996 |
| Main CPU | NEC D70632GD-20 (V70) @ 20 MHz (40 MHz crystal ÷ 2) |
| Sound CPU | Z80 (Z0840008PSC) @ 8 MHz — ⚠️ see below |
| Sound | YMF271 @ 16.9344 MHz + YAC513 |
| System controller | MS32 SYSCTRL @ 48 MHz |
| Sprites | dedicated generator @ 6 MHz (48 ÷ 8) |
| Scan rate | ~15.6 kHz / ~59.4 Hz — 384 × 263, 320 × 224 visible |
| PCB format | JAMMA |
Expected clocks — measurement table ✅¶
| Component | Expected clock | Role |
|---|---|---|
| NEC V70 | 20 MHz | Main CPU |
| Z80 | 8 MHz | Sound CPU — ⚠️ uncertain |
| YMF271 | 16.9344 MHz | sound |
The Z80's clock is not established
The driver says so outright: the 8 MHz figure comes from notes, and it hesitates between two possible origins — 40 MHz ÷ 5 or 48 MHz ÷ 6 — without settling it.
Both give 8 MHz, so the displayed value is probably right; but the clock path itself is not known. On a sound fault, do not assume which crystal it depends on.
Architecture¶
Three things to tell apart in repair:
- the V70, NEC's 32-bit processor, clocked at 20 MHz from a 40 MHz crystal;
- the MS32 SYSCTRL, a system controller fed by a separate 48 MHz crystal, which also drives the display and the sprite generator;
- the sound stage, on its own, with its Z80 and the YMF271.
Two master crystals, not one
Unlike a board such as the Namco ND-1, where everything derives from a single crystal, the MS32 has two: 40 MHz for the CPU, 48 MHz for the system and video. A display fault therefore does not implicate the processor's crystal, and the other way round.
The CPU ↔ sound link¶
The V70 and the Z80 exchange through two 8-bit registers, one in each direction. It is an architectural detail with a practical consequence: sound that is entirely absent while the game runs normally points at that link as much as at the Z80 itself.
Notable games¶
Hayaosi Quiz 2 and 3 (1994) · Best Bout Boxing (1994) · Super Chinese 2 (1994) · Desert War (1995) · Game Tengoku (1995).
Common faults¶
| Symptom | Probable cause | Next step |
|---|---|---|
| No picture | the 48 MHz crystal or the SYSCTRL | ⚠️ not the CPU's 40 MHz crystal |
| Silent board | V70 or its 40 MHz crystal | Two separate crystals: do not confuse them |
| No sound | Z80, YMF271, or the two-register link | Three points, not one |
| Corrupt sprites | sprite generator (6 MHz) | Derived from the 48 MHz |
| Settings lost | board depending | — |
Repair (technician)¶
- Separate the two clock domains. 40 MHz for the CPU, 48 MHz for the system and video. That is the first thing to establish on a partial fault.
- The V70 is the same processor as Sega's Multi 32 — a useful comparison point if you have both to hand. → Sega System 32 / Multi 32
- Do not assume the Z80's crystal: the driver itself does not know which one it depends on.
→ 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.
- NEC V70 → 20 MHz (Main CPU)
- Z80 → 8 MHz (CPU son — ⚠️ incertain)
- YMF271 → 16,9344 MHz (sound)
No clock on the NEC V70 (20 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.
Modernisation & mods¶
- No suicide: no battery-backed protection.
- Scan rate 📺: ~15.6 kHz — ordinary 15 kHz chassis.
- ⚠️ Do not host ROMs — method only.
Emulation & FPGA¶
MAME covers the platform (jaleco/ms32.cpp), including the exchange protocol
between the V70 and the Z80.
Photos / assets¶
(To take: the two master crystals (40 and 48 MHz) side by side, the V70 and the YMF271.)
Sources & attribution¶
Text (synthesised here; sources listed for attribution):
- MAME —
src/mame/jaleco/ms32.cpp(BSD-3-Clause / GPL): NEC D70632GD-20 (V70) at 20 MHz (40 MHz ÷ 2), Z80 Z0840008PSC at 8 MHz with the explicit note “Clock from notes (40MHz / 5 or 48MHz / 6?)”, YMF271 at 16.9344 MHz, YAC513, the MS32 SYSCTRL and sprite generator on the 48 MHz crystal, 384 × 263 (320 × 224 visible) timing at 48 ÷ 8; and the description of the pair of 8-bit registers carrying communication between the V70 and the Z80 — https://github.com/mamedev/mame/blob/master/src/mame/jaleco/ms32.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.
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