Alpha Denshi / ADK¶
Time Soldiers, Sky Soldiers, Gold Medalist, Gang Wars. Alpha Denshi — later ADK, then SNK's in-house studio — built its 68000 boards around an in-house microcontroller able to write anywhere in main memory. It is not merely protection: it is an active part of the game, and it is still not fully understood.
Identification¶
| Field | Value |
|---|---|
| Manufacturer | Alpha Denshi / ADK (Japan) |
| Years | 1987-1990 (“II” and “V” series) |
| Main CPU | M68000 — 10 MHz (20 ÷ 2) on V boards, 8 MHz elsewhere |
| Sound CPU | Z80 — 6 MHz (24 ÷ 4) |
| MCU | custom Alpha microcontroller — ⚠️ see below |
| Sound | YM2203 + YM2413 + custom ALPHA-VOICE88 DAC |
| Pixel clock | 6 MHz (24 MHz crystal ÷ 4) |
| PCB format | JAMMA |
Many clocks remain to be verified
The driver carries “TODO: verify me” on the M68000 at 8 MHz, the Z80 at 6 MHz, the YM2203 and the YM2413. Only the values derived from the 20 and 24 MHz crystals on V boards are settled. Do not condemn a crystal on the strength of these figures.
“II” boards and “V” boards¶
Two generations, distinguished by MAME:
| II series | V series | |
|---|---|---|
| Memory | less | more |
| Colours | — | twice as many |
→ That is the first thing to establish when identifying one of this maker's boards.
⚠️ The Alpha microcontroller¶
This is the platform's heart, and its difficult part.
It writes everywhere in main memory
Alpha's custom MCU is not a simple lock: it is able to write anywhere within main memory. It takes an active part in the game — timers, events, boss logic.
The repair consequence: a failing MCU does not announce itself with a “protection screen”. It produces erratic behaviour elsewhere — a boss that never times out, a wrong stopwatch, a sequence that never triggers. Looking for the fault in the game rather than in the MCU is a natural mistake.
Behaviours still approximated in emulation
The driver says so: on Gold Medalist the dash-event timers depend on the MCU's interrupts, and the value used is an approximation — MAME moved from 180 Hz to 100 Hz after comparing against a stopwatch, noting that fine tuning would need hardware probing or a decap of the MCU.
Another MCU interrupt routine has a path that is “never taken into account, what is it for?” — a question left open.
→ Comparing a real board against emulation therefore settles nothing on those particular points.
Bootlegs are told apart by the MCU
The pirate Gold Medalist carries a 68705 in place of the Alpha controller. If the chip is an identifiable 68705, the board is not original.
Notable games¶
Time Soldiers (1987) · Battlefield (1987) · Sky Soldiers (1988) · Gold Medalist (1988) · Sky Adventure · Gang Wars · Super Champion Baseball.
Common faults¶
| Symptom | Probable cause | Next step |
|---|---|---|
| Incoherent game behaviour | Alpha MCU | It writes into main memory: the fault shows up somewhere other than at the chip |
| Boss that never times out | MCU (timing) | Documented on Sky Soldiers |
| Wrong stopwatches (Gold Medalist) | MCU (interrupts) | ⚠️ emulation itself is only approximate here |
| No sound | Z80, YM2203/YM2413, or the ALPHA-VOICE88 | Three separate stages |
| Sound CPU crashes | known on II and V boards | The driver flags mishandled nested NMIs |
| No picture | 68000 or a crystal | ⚠️ several clocks unverified — compare against a good board |
Repair (technician)¶
- Do not look for the fault where it shows. On this platform a tired MCU announces itself through gameplay anomalies, not an error screen.
- Establish II or V before comparing anything: memory and colours differ.
- The MCU has no replacement, and its contents were only obtained by decapping on some models. A board whose MCU dies is a hard board to save.
→ 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. There is no measurement table for this platform — MAME's sources yield nothing usable for it. Any frequency quoted under Architecture on this page serves as a marker; otherwise compare against a working board rather than against a number: an invented value condemns healthy parts. → PCB diagnosis
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 battery suicide — but the MCU plays an equivalent role: without it the game does not run properly.
- ⚠️ Do not host ROMs or MCU dumps — method only.
Emulation & FPGA¶
MAME covers the family (alpha/alpha68k.cpp). The DIP locations are verified
against the manuals for several games — but the MCU emulation remains partly
approximate, as the driver acknowledges.
Photos / assets¶
(To take: the Alpha microcontroller — the part worth photographing —, a II board and a V board side by side if possible, and the ALPHA-VOICE88 DAC.)
Archived original documents ✅¶
Documents archived locally, found in Internet Archive's arcademanuals collection on 14 August 2026 and identified from their title page. ⚠️ The items declare no licence.
- PDF — alpha-denshi-sound-board-no59-mc07-schematics.pdf — Alpha Denshi Co. — SOUND BOARD NO.59 MC 07, schematic, 4 sheets, revision 1.1. ⚠️ The only internal Alpha Denshi document on this page: the others are operating manuals. Sheet 1 gives the CPU and its 8155, sheet 2 the 7220 clock, the address decoding and the 2764 / 27128 EPROM bank. Via Internet Archive
- PDF — romstar-time-soldiers-installation-manual.pdf — TIME SOLDIERS — Installation Manual, Romstar, Inc. (Torrance, California), © 1987, 16 pp. ⚠️ The cover reads "Licensed From SNK Corporation": the game is developed by Alpha Denshi, licensed by SNK, distributed in the US by Romstar. Three names for one board — enough to spend a long time hunting a manual under the wrong one. Via Internet Archive
- PDF — snk-sky-soldiers-service-instructions.pdf — SKY SOLDIERS — Service Instructions, SNK, 4 pp. Via Internet Archive
- PDF — gold-medalist-dip-switch-amendment.pdf — Amendment for DIP switch list — GOLD MEDALIST, 9 pp. ⚠️ Not a manual, a correction notice: "Please note that we have amended Dip Switch for GOLD MEDALIST as follows". It restates DIP SW no. 1 in full — game type (non select / select), style (table, upright 4P, upright 2P), computer demonstration, and 100 m dash speed (14 or 10 beats for maximum speed). The document also states that the previously published control wiring diagram contained mistakes, corrected overleaf. Via Internet Archive
Sources & attribution¶
Text (synthesised here; sources listed for attribution):
- MAME —
src/mame/alpha/alpha68k.cpp(BSD-3-Clause / GPL): the 68000 + Z80 + custom Alpha microcontroller architecture, the latter “able to write to anywhere within main memory”; the II / V board distinction (“V boards have more memory and double the amount of colours”); a 24 MHz ÷ 4 pixel clock, M68000 at 20 MHz ÷ 2 and Z80 at 24 MHz ÷ 4 on V boards, with “TODO: verify me” on the other values; the custom ALPHA-VOICE88 DAC; the 68705 in pirate Gold Medalist versions; the approximated timers in Gold Medalist (180 Hz replaced by 100 Hz, fine tuning needing “HW probing and/or a MCU decap”), the never-taken interrupt routine left unexplained, and the sound CPU's nested NMIs — https://github.com/mamedev/mame/blob/master/src/mame/alpha/alpha68k.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.