Last Updated: 4/19/2024
Article Credit: ShootTheCore, wickerwaka, ekorz, System11, Apocalypse
Main Board
The Main Board is largely identical across all Irem M92 games. It is labeled either M92-A-A or M92-A-B.
Photo Credit: ShootTheCore
Photo Credit: ShootTheCore
Early boards have less Object RAM (16K) installed at locations IC43 & IC44 than later boards (64K) – selectable by jumper J2 – but all M92 games are confirmed to function correctly with the 16K board. Thus, the difference in RAM was likely determined by parts cost at the time of manufacture.
Photo Credit: ShootTheCore
Photo Credit: ShootTheCore
Notable ICs
| IC | Function | Silkscreen Label | Location |
| NEC D71036L V33 | Main CPU | H8 | |
| Nanao GA20 | Sound FX Samples | IC32 GA20 | B6 |
| Nanao GA21 | SRAM DMA and Address Generation for GA22 | IC42 GA21 | M7 |
| Nanao GA22 | Graphics Rendering | IC63 GA22 | M10 |
| YM2151 | FM Sound Chip | IC33 | C6 |
| YM3014 | Sound D/A Converter | IC208 YM3014 | C5 |
Secondary Board
The Secondary Board layout varies across the M92 games.
The Sound CPU resides on the secondary board and utilizes an encryption mechanism – see “Copy Protection” below.
Photo Credit: ShootTheCore
Photo Credit: ShootTheCore
Photo Credit: Ebay
| Game | Board Model | Sound CPU Model | Notes |
| Blade Master / Cross Blades | M92-B-A M92-D-A | ||
| Dream Soccer 94 | |||
| GunForce | M92-B-A | ||
| GunForce II / GeoStorm | |||
| Hook | M92-D-A | ||
| In The Hunt / Kaitei Daisensou | M92-E-B | ||
| Lethal Thunder / Thunder Blaster | M92-C-B | ||
| Major Title 2 / The Irem Skins Game | M92-B-F | Only M92 game to utilize an EPROM for saving scores. | |
| Mystic Riders / Gun Hoki | M92-B-B | ||
| Ninja Baseball Bat Man / Yakyuu Kakutou League-Man | M92-F-A M92-Z-C | ||
| Perfect Soldiers / Superior Soldiers | |||
| R-Type Leo | M92-C-N | ||
| Undercover Cops | M92-E-B |
Notable ICs
| IC | Function | Silkscreen Label |
| Nanao 08J27261A1 V35 | Sound CPU | IC10 |
| Nanao GA23 | ROM Addressing (Assumed) | IC23 08J27504A1 |
Board Variants
M92 boards manufactured for the Korean region have several noticeable differences from boards manufactured for other territories:
- The green silkscreen is a lighter shade of green.
- The JAMMA connector does not have a key notch.
- SRAM ICs on M92 boards for other regions are manufactured by NEC whereas on the Korean boards they are manufactured by Hyundai and Goldstar.
- The amplifier heatsink is physically smaller, and is colored silver rather than black.
- One or both boards may be missing markings for the board type on the silkscreen.
- A metal serial number tag is not present in the upper-right corner of the A Board.
Photo Credit: ShootTheCore
Photo Credit: ShootTheCore
There are also single-board bootlegs of several M92. They are much smaller than original M92 boards and thus are easily distinguished. Compared to the original games, bootlegs often omit animation frames, shorten the music tracks and gameplay slows down more frequently.
Photo Credit: ShootTheCore
Common Issues and Quirks
- The factory-installed capacitors are colored green or brown. The ELNA brand brown-colored capacitors are notorious for leaking and should be replaced ASAP.
- Video output is darker than average with this hardware.
Protection Mechanisms
The Nanao 08J27261A1 V35 Sound CPU on the B Board enforces a security scheme where each game’s sound CPU code is encrypted in ROM and then decrypted by a key specific to the model of CPU. Thus, if the game ROMs are swapped to another game without decrypting the sound CPU code of the new game and re-encrypting the code to match the encryption scheme of the old game, the sound CPU will crash and the game won’t have sound.
Changing jumpers J1 and J6 adjacent to the Sound CPU from “S” to “N” disables the decryption mechanism and allows the CPU to run decrypted Sound CPU code directly.
Capacitor List (credit: System11)
Main Board
| Location | Capacitance | Voltage | Part No. |
| C201 | 1 uF | 50 V | ECA-2EM010 |
| C202 | 470 uF | 25 V | ECA-1EM471 |
| C203 | 220 uF | 10 V | ECA-1AM221B |
| C204 | 22 uF | 25 V | ECA-1EM220I |
| C209 | 100 uF | 25 V | ECA-1EM101 |
| C210 | 1 uF | 50 V | ECA-2EM010 |
| C213 | 47 uF | 16 V | ECA-1CM470I |
| C215 | 1 uF | 50 V | ECA-2EM010 |
| C216 | 1 uF | 50 V | ECA-2EM010 |
| C217 | 1 uF | 50 V | ECA-2EM010 |
| C218 | 1 uF | 50 V | ECA-2EM010 |
| C219 | 1 uF | 50 V | ECA-2EM010 |
| C236 | 100 uF | 25 V | ECA-1EM101 |
Resistor List (credit: fuzzbuddy)
- R201 – 1KOhm
- R203 – 100KOhm
- R205 – 4.7KOhm
- R208 – 4.7KOhm
- R209 – 2.7KOhm
- R211 – 10KOhm
- R213 – 10KOhm
ROM Details (credit: MAME Source, ekorz)
| Label | Location | EPROM Part No. | Function |
| H0 | B Board | 27C020 (256kb) | Main CPU |
| L0 | B Board | 27C020 (256kb) | Main CPU |
| H1 | B Board | 27C020 (256kb) | Main CPU |
| L1 | B Board | 27C020 (256kb) | Main CPU |
| SH0 | B Board | 27C512 (64kb) | Sound CPU |
| SL0 | B Board | 27C512 (64kb) | Sound CPU |
| C0 | B Board | 27C040 (512kb) | Background Tiles |
| C1 | B Board | 27C040 (512kb) | Background Tiles |
| C2 | B Board | 27C040 (512kb) | Background Tiles |
| C3 | B Board | 27C040 (512kb) | Background Tiles |
| 000 | B Board | 27C080 (1024kb) | Sprites |
| 010 | B Board | 27C080 (1024kb) | Sprites |
| 020 | B Board | 27C080 (1024kb) | Sprites |
| 030 | B Board | 27C080 (1024kb) | Sprites |
| DA | B Board | 27C040 (512kb) | Audio Samples |
Schematics (credit: wickerwaka)
Original Irem schematics are unavailable for M92.
wickerwaka developed a MiSTer FPGA core for the Irem M92 platform, and generated the following schematics (Source):
Additional Resources
| MAME M92 Driver Source Code | https://github.com/libretro/mame2016-libretro/blob/master/src/mame/drivers/m92.cpp |
| wickerwaka MiSTer FPGA Source | https://github.com/wickerwaka/Arcade-IremM92_MiSTer/tree/main |
| System 11 Blog – Irem Games and Leaking Capacitors | Website is offline – PDF Archived on August 2017 |