As I mentioned in the previous post, I wanted to expand the chip RAM to 1 MB to play some WHDLoad games. With the new adapter this is possible without motherboard modifications.
However, there is one problem with the modification: when installed, my Vampire 500 V2+ accelerator doesn’t fit in the Amiga anymore!
The solution is quite simple: from two 64-pin DIP sockets and some ribbon cable it’s possible to build an adapter that moves the Vampire few centimetres away from the Fat Agnus socket and leaves space for the chip RAM adapter. I first thought about making some PCBs for a more solid adapter, but there is a capacitor right next to the CPU socket, and fitting a PCB there would be difficult. The flexible ribbon cable leaves more space for the capacitor.
I had some 40 pin ribbon cable, so I cut two 32-pin pieces from it to form the connection. The wires on one end of the cable were separated, and every other wire was cut shorter. Then the ends of the wires were stripped from insulation.
The ends of the shorter wires were wrapped around the pins of the socket on one side, and then soldered in place. After this, the longer wires were wrapped around the pins on the other side.
When all pins have been soldered, extra length of the pins was trimmed away.
Next step was to work on the other socket. First I measured the correct place for the socket by fitting this inside the Amiga and marking where to cut the wires. Then every other wire was cut shorter the same way as on the other side.
Preparing the short wires for soldering to the other socket was more time consuming than with other connections, as they had to be tinned first for insertion to the socket. As the wires are connected together, it’s not possible to insert and solder them one-by-one, but they all should fit to the socket simultaneously, and if the thin wires of each conductor get separated, it’s not possible to insert them to the socket.
For the chip RAM modification, an additional connection to the pin 47 of the CPU from the Fat Agnus in needed. This is the additional red wire in the images.
When the short wires for the one side had been soldered, the longer wires for the other wires were easier. It was possible to prepare and solder them one by one, so it was enough to just twist the thin wires of each conductor together, insert them to the socket and solder in place.
When all connections had been soldered, I used hot glue for attaching some insulation to prevent accidental shorting of the connections. I also attached a socket at the end of the cable to pin 47 for connecting the Fat Agnus.
When installed in the Amiga, this moves the CPU socket towards the edge of the machine, and the Vampire board fits tightly between the cover of the Amiga and Fat Agnus. Because the cable is slightly flexible, it’s possible to adjust the position of the Vampire for a good fit.
When the Amiga was turned on, I now have 1 MB of chip RAM with the Vampire. Finally it’s possible to play Xenon 2 with WHDLoad!