Gameboy 4MB 32KB FRAM MBC3 with RTC+Rumble plus 2x 2MB Mode Flash Cart (Build it yourself)


Usually MBC3 chips only allow for 2MB of flash however by adding a special logic chip, we can extend the flash size to 4MB so you can future proof your RTC cart. There is an MBC30 chip which does support 4MB but carts usually go for $12-15 and aren’t very common where as MBC3 carts go for $1-3 and are everywhere. Re-flashable with any flasher like GBxCart RW that supports the MBM29F033C chip via the audio pin method. Uses FRAM to keep the save even when the battery runs out.

As most users build MBC3 carts themselves, we’re providing this option so please ensure you know how to solder and you will need to source all the parts yourself (check the list below) and we will only provide the PCB and special logic chip (unsoldered). Please note that not all MBC3 original carts have the RTC crystal/parts, the most common ones that do are Pokemon Gold/Silver.

New v1.2 PCB allows for Rumble and 2x 2MB ROM Mode which allows you to switch between 2 ROMs such as Gold/Silver to share the same save file (shell cutting/trimming is required to fit the switch, the shell won’t close unless you trim the top part of the shell but be sure not to cut the little notch).

SKU: N/A Category:


Build it yourself parts required:
MBC3 chip (take from an MBC3 cart)
MBC3 8 pin power management chip (take from an MBC3 cart)
4MB MBM29F033C Flash
CR2032/CR2025 Battery holder + CR2032/CR2025 battery
32.768 KHz crystal (take from an MBC3 cart)
330K resistor 0603 (take from an MBC3 cart)
2x 20pF capacitor 0603 (take from an MBC3 cart)
1K resistor (take from an MBC3 cart)
10K 0603 resistor
10K 0805 resistor
4x 0.1uF 0603
Gameboy Cartridge

For v1.2 these parts are needed for rumble:
47 or 100 Ohm 0805 resistor
10K 0805 resistor
2N7002 Mosfet SOT-23
DSS115U SOD-123FL Diode (or any other 50V+ diode)
Pager Flat Vibration Micro Motor DC 3V

For v1.2 these parts are needed for 2x 2MB ROM Mode:
SPDT MSK-12C02 SMD Switch
You will need to modify the cartridge for the switch

How to use the rumble motor
You need to write the byte 0x20 to 0x4000-0x5FFF. Usually games write 0x08 but that would conflict with the RTC so you need to patch games to use 0x20 instead. For Pokemon Pinball we have an example patch to apply but it doesn’t appear to activate the rumble strong enough – you could lower the resistor if need be.

How to use 2x 2MB ROM Mode
Check the picture as you need to bridge jumper pads with solder and un-bridge another jumper pad. You’ll also need a special program to flash both ROMs to the cart: 2x 2MB ROM Mode Flasher.

ROM: 4MB Flash (MBM29F033C)
FRAM: 32KB (Data retention of 20-50 years)
MBC: MBC3 original chip

The power consumption of MBC3 when powered from the battery appears to be around 2.3uA so a CR2032 should last around 7-10 years.

The PCB finish is ENIG, Gold fingers (on the edge connector) with a 45 degree bevel to give the maximum life for insertion/removal of the cartridge.

If you will be installing this flash cart in an original shell, it is very difficult due to the CR2032 battery holder but it is possible, some users prefer using a CR2025 battery holder instead.

Additional information

Weight 10 g
PCB version

RTC, Rumble and 2x 2MB mode switchable ROM (v1.2)

Flash carts

Gameboy carts, Low power, MBC3 support, RTC support, Saving supported


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