The easy way to make an EEPROM Cartridge for the VFX/SD-1 family of synthesizers is
to convert a VFX ROM cartridge to an EEPROM. The circuit boards are identical. Only the
memory chip needs to be changed, and two jumper wires need to be moved.
Here is a link that explains the entire job, with pictures.
I've made five such conversions and they all worked perfectly.