CPU Board 4164/41256 RAM Modification.
The 4116 RAM that shipped with Williams video games can be prone to (apparent) failure.
There are a number of reasons for this:
The triple voltage rail design requires +5v, +12v and -5, so they are sensitive to Power Supply issues.
They run very hot due to high power requirements increasing the temperature inside your game.
The sockets Williams used to fit them in are often single wipe sockets giving a poor connection (replace SCANBE sockets regardless).
Corrosion damage from the 3x AA batteries can cause issues with the RAM sockets.
Power wiring making poor connections reducing delivered voltages.
The 4164/41256 RAM, however only needs a +5v Power Supply and has a similar pinout.
If you look at the diagram you and examine the differences between the three RAM types, only Pins 1, 8 and 9 change. Fortunately for us the -5v and +12 supplies at pins 1 and 8 are only used for the 4116 RAM so we can connect them to +5v and the extra address lines will pulled up.
To fit 4164/41256 RAM without having to modify you games CPU board or wiring harness we need an adaptor that will plug in between the CPU board connector 1J3 and the Power Supply connector 1P3.
The diagram shows the wiring for the adaptor, if you don't fancy making one then there are a number of commercial suppliers of these or you can make your own.
Notes:
Pins 1 (Ground) and 6 (+5v) are not normally connected to 1P3 factory wiring looms.
Pins 6 and 7 (both +5v) of 1J3 are joined on the PCB.
Pins 1, 2 and 3 (all ground) of 1J3 are joined on the PCB.
Adaptors like this one are the perfect no fuss solution to converting your game to use 4164 RAM.
(Note: The adaptor shown does not support 41256 RAM as the -5v line is not connected but adding a single jumper can achieve this easily)
If you want to build your own using wires rather than a pre-built PCB, here are some useful part numbers:
9-pin male connector Molex 09-65-2098 (1 required).
9-pin female housing Molex 26-03-4090 (1 required).
Trifurcon contact Molex 08-52-0113 (8 required).
Use with 18AWG wire and use heat-shrink or sleeves to insulate the solder connections on the male connector.
