Williams Video Decoder PROM Replacements
The Video Decoder PROMs used on Williams video games CPU boards are Harris 7641 Bipolar PROMs. These obsolete devices need special equipment to program them and it is hard to source bank devices now.
The following games use Video Decoder PROMs 1-6:
Video Decoder 1: Early Series Defender (D8356 CPU Board).
Video Decoder 2 & 3: Later Series Defender (R8570 CPU Board).
Video Decoder 4 & 5: Stargate (R8948 CPU Board).
Video Decoder 4 & 6: Robotron, Joust, Sinistar, Splat! (R8731 CPU Board).
Video Decoder 4 & 6: Bubbles (R9663 CPU Board).
Video Decoder 4 & 6: Blaster (D9917 CPU Board).
In the past where replacement 7641 PROMs (or equivalents) were not available the solution was to modify the board to use a 2732 EPROM instead. This can be problematic though as it modifying the board and often the 2732 was not fast enough causing occasional screen issues.
My current solution for this it to use an adaptor board which uses at 27512 OTP PROM, this device is more than fast enough and is a current product easily sourced from regular supply chains.
The adaptors I make have jumpers on the bottom to allow you to select the desired video decoder number making them usable for any configuration without needing to reprogram them.
When I have them available for sale they will appear on my For Sale page.
