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Procedure
1. Start by opening the cartridge. I was surprised to find out that the entire VPC cartridge assembly (at least for the two carts I have) is held together by friction. It's not welded. It's not glued. The plastic shell has a front half and a back half; four plastic pins on the back half fit snuggly into four plastic sleeves on the front half; and the circuit board is held in the back half, again by friction. You can just pull it apart, but of course, be careful! I find it easiest to start at the bottom, pulling the plastic "fingers" apart to open the case a tiny bit, then pull a bit with finger pressure at the top, then keep alternating between the top and bottom until the case finally separates.
2. Remove the circuit board from the case. It's wedged pretty tight, but you can just wiggle it out.
Remember that the component side of the board was facing you before you removed the board from the back half of the case, so you get it in right when you put the whole thing back together.
3. Note the notch along the top edge of the 27C256 ROM chip. When you put the EEPROM in its place, the notch of the EEPROM should be in this same position.
4. Use your de-soldering equipment to remove the ROM and the two 0-ohm resistors marked R3 and R6.
If you don't have professional de-soldering equipment, you may find that you need to sacrifice the original ROM, by cutting its pins and removing the main body of the ROM, then individually de-soldering what's left of the pins from the circuit board. If you don't do this, you run the risk of damaging the board when trying to get all 28 pins free at one time.
5. Clear the solder from the holes for R4 and R5, the ones that were "missing" when you started.
6. Solder the zero ohm resistors you pulled from R3 and R6 back in as R4 and R5, or just use a piece of wire for each if you wish.
7. Now you must make a choice. Either you solder the EEPROM directly on to the cartridge board, or you solder in a 28-pin socket and plug the EEPROM into the socket.
I personally put in a socket, but then I found out the combined height of the EEPROM and socket is too much, and the cartridge case does not completely go back together. And as a result, it's a little tight plugging this new cartridge into my VFX. If I was to do it over again, I'd probably skip the socket.
Whatever you do, remember to be certain that the notch on the EEPROM chip is a the top!
8. Double check your work to make sure you don't have any bad solder connections or solder bridges.
9. Re-assemble the cartridge. (Again, the component side of the circuit board should face you, not the solder side, when you put the cartridge back together.)
10. Put the new cartridge in your VFX and try it out!
Now, what does the VFX do with a blank EEPROM? Will it reject it? I found that when I tried to write a single preset to the "new" cartridge, the VFX found it was blank and decided to copy my whole INT bank out to the cartridge. How wonderful; I suddenly have a EEPROM cart with completely valid data!
Or perhaps I shouldn't say suddenly. Those who haven't used an EEPROM cartridge before will probably need to be warned: writing data on these chips is a very slow operation! You will get a flashing "PLEASE WAIT" message that will last quite some time. When it's taken long enough that you start to get nervous that you did something wrong and your VFX is going to be damaged, you're about 70% done with the initial programming of the cartridge. At least, that's how it was for me. I didn't time the operation, but I would say it was maybe somewhere between 2 and 4 minutes. (Reading from them, on the other hand, is FAST, as you'd expect from a ROM chip.)
