Gameboy 4MB 32KB FRAM MBC3 with RTC+Rumble plus 2x 2MB Mode Flash Cart


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.

3 Oct 2020 – More expected in 2-3 weeks

This listing is for the pre-assembled version. If you wish to build it yourself, check out the build it yourself listing.

New v1.2 PCB allows for Rumble (supply your own motor, requires game patching to use, check example) 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).

If you would just like a regular 4MB cart, you can proceed with the default options we’ve set.

SKU: N/A Category:


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 CR2025 should last 5-7 years and 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 and 2x 2MB mode switchable ROM (v1.2), RTC, Rumble components (no motor) and 2x 2MB mode switchable ROM (v1.2)

ROM mode

4MB mode, 4MB mode (populate switch), 2x 2MB mode (populate switch)

Cart Colour

Grey, Clear Green, Clear Blue, Clear, Yellow


CR2025, CR2032 (can make cart shells bulge), CR2025 holder (no battery), CR2032 holder (no battery, can make cart shells bulge)

Pre-loaded ROM

I will provide a ROM to flash by email, Not required or N/A

Flash carts

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


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