If you still didnt buy the MegaCard to upgrade your MegaPC, there is another useful upgrade. Replacing the Megadrive ASIC on the ISA card as it's an early version with a bug. Beware, you need to be careful when removing the bugged ASIC and putting a new one coming from a Megadrive donor. It will let you use flash cartridges with more success like the MegaEverdrive PRO (other source here).