WIKI_ENTRY :: retrogaming

DIY Game Boy Flash Cartridge with a ROM Adapter Board

Technical wiki guide for building a Game Boy flash cartridge using a ROM adapter board and compatible donor cartridge PCB.

wiki topic - retrogaming updated - May 27, 2026 requires fine soldering

// 01 - Overview

Adapter-based flash cartridge build

Assembled Game Boy ROM adapter board installed on a cartridge PCB — **Figure 1:** assembled ROM adapter board installed in a donor Game Boy cartridge.

The idea is to reuse an original Game Boy cartridge PCB that already has a compatible mapper and footprint. After desoldering the read-only mask ROM, the adapter board is soldered where the original ROM was installed. Then a small number of extra signals are wired manually.

For a 2 MB flash ROM adapter, the practical wiring is normally three extra signals: RESET, RW and A20. For a 4 MB flash ROM adapter, add A21.

This adapter is only for 32-pin SOP parallel ROM footprints. Before soldering anything, verify that the donor cartridge ROM footprint and pinout match the adapter board.

// 02 - Compatible cartridges

Known compatible donor PCB families

Compatible cartridge PCBs include several MBC5, MBC3 and MBC7 mapper families. Other cartridges can also be compatible if the cartridge ROM footprint matches the adapter board and uses the same ROM pinout.

MapperKnown PCB codesOriginal configuration

MBC5 DMG-A02-01 DMG-A06-01 DMG-A07-01 ROM 256/512/1024 KB, optional RAM and battery depending on board

MBC3 DMG-KFDN-10 DMG-KFDN-01 DMG-KECN-SP ROM 256/512/1024 KB, RAM, battery and optional RTC/timer

MBC7 DMG-A40-01 ROM, small RAM, battery and tilt hardware

Treat this table as a starting point, not a complete compatibility database. The donor board must be inspected before using it: mapper type, ROM footprint, RAM support and battery requirements all matter.

// 03 - Pinout check

Confirm the 32-pin SOP ROM footprint

ROM adapter SOP32 pinout reference — **Figure 2:** SOP32 ROM adapter pinout reference.

The adapter board is designed around a parallel ROM-style pinout. The donor cartridge must expose the right mask ROM footprint so the adapter can replace the original read-only ROM without rewiring every address and data line manually.

RESET

Reset/control signal. On MBC5 boards this may be marked as /RST.

Write control signal. On MBC5 boards this may be marked as /WR.

A20

Extra address line used by larger flash ROM capacities.

A21

Only needed for the 4 MB adapter variant.

// 04 - Adapter schematic

Adapter board reference

ROM adapter schematic revision A — **Figure 3:** ROM Adapter schematic, revision A.

The schematic documents how the flash ROM adapter maps onto the cartridge ROM footprint. Use it as the reference when checking continuity, signal names and any mismatch between donor cartridge and adapter board.

// 05 - Assembly

Desolder the mask ROM, install the adapter, wire the extras

MBC5 ROM adapter wiring reference — **Figure 4:** MBC5 adapter wiring reference.

Game Boy adapter board compared with full wire ROM method — **Figure 5:** adapter method compared with full manual wiring.

step_01

Remove the original mask ROM

Desolder the read-only ROM from the donor cartridge carefully. It is normally marked as U1 2M/4M/8M-MROM and is usually located below the backup battery on compatible boards.

step_02

Clean the footprint

Clean the remaining solder before installing the adapter. Flux and copper braid make the next soldering step much safer and reduce the chance of bridges between SOP pads.

step_03

Solder the ROM adapter board

Place the adapter in the old ROM footprint and solder it as the ROM replacement. Check alignment before committing all pins.

step_04

Wire the required signals

Add the extra wires for RESET, RW, A20 and, only for 4 MB adapters, A21. The wires can be soldered directly to the mapper IC or to a via/trace carrying the same signal.

// 06 - Programming setup

Erase first, then program as a flash cartridge

Game Boy cartridge flashing software setup — **Figure 6:** software setup for flashing the cartridge.

The first time the cartridge is programmed, erase the flash memory first. Use the Erase Flash button before writing a ROM.

After erasing, program it like other supported flash cartridges: choose MBC AUTO, select the appropriate flash/ROM size, and set the RAM size according to the donor board.

// 07 - References

Useful external references

These links are useful when identifying donor boards and checking PCB variants.