Ensoniq VFX cart adapter
Recently found a lightly damaged Ensoniq VFX and a VPC-102 cartridge in the dumpster. Surprisingly, it turned out a working one! Yay for that \o/
Whilst repairing the synth, I couldn’t resist the temptation to also tear apart the cart and see how it works: This turned out to use a bog-standard 27C256 EPROM circuit. Less surprisingly, in no time I found myself thinking about a ROM adapter.. Yep, let’s haxx0r!
My cart mod is based on Steve Wahl’s cart conversion, but I wanted to make the ROM chips easily replaceable. So, instead of having the chip on the board I decided to install a ZIF-socket in a 90° angle and have it resting on top of the VFX panel. Additionally, I replaced the two (zero ohm) bridging resistors with DIP-switches to allow using both EPROM and EEPROM chips.
Despite the combination might look like very easy to break, it is actually very solid. It’s the combination of several little things that contribute to this. First, I cut a groove to the bottom of the socket to which the board slots in a little. Second, I used the four topmost pin rows to “anchor down” the socket by either direct solder connection to the board or by using component feet surplus in-between. Additionally, pin pairs 1 and 28 rest against the bottom of the board whereas pins 2 and 27 are on top. Third, I hotglued a L-bracket between the bottom side of PCB and socket. This helps to counter the weight applied when ZIF locking lever is operated. Fourth, once the case is assembled the combination rests against it too. And fifth, the gasket provides additional support once the cart is installed.
The DIP-switches select between ROM and EEPROM, 1+4 for the former and 2+3 for the latter. It is supported by a dab of hot glue and the component feet surplus. I also relocated the 100nF decoupling capacitor as relying entirely on the wire-wrap connection felt a bit unsecure.
Next up, time to locate some EEPROM chips to test how writing sounds works! Seeing that there are plenty of (SYSEX) presets available on the net, it might not be a bad idea to browse through these and make a ROM set of “something usable”. I also have a spare PLCC-to-DIP adapter, and I plan to test this with some 28C256 PLCCs. Should contribute increasingly nerdy flavor to the appearance.. ;)
If you have any VPC (or other) VFX rom dumps to share, I’d appreciate a download link!