4116 to 4164 (and/or 41256) mod

for Williams CPUs

If you want your Williams games to run reliably then you need to ditch that crappy 4116 DRAM! Those tri-voltage devices are power hungry and prone to failure. There are single-voltage, lower power chips that can be adapted to run in their place. Here's a quick and easy way to modify your Williams CPU to run 4164 (and/or 41256) directly. After performing the mod you can throw out all that 4116 and pop in the more reliable DRAM. This mod is for people who are comfortable doing simple soldering. If that's not you, then you should consider another method: 4164 Power Adaptor Harness for Williams Games.

You perform these modifications AT YOUR OWN RISK!!!

The top photo shows the two locations on the back of the Williams CPU where the changes will be made. Below that are close-ups of the two areas. Just for reference, the PCB shown is a Robotron, 5770-09656-00 REV. C.
Here are the changes explained:

1) Cut the trace indicated by the red arrow. This removes the +12V supply to all of the RAM (and only the RAM).
[TIP] Cut traces using a thin incision close to the solder point. That way the change is easily reversible if need be (the connection can be re-established like a split solder pad, and someone would have to look really hard to know that a change was ever made). I can't fathom why anyone would decide to go back to using 4116... but I suppose it doesn't hurt to leave that option open.

2) Solder the link as shown. This will supply +5V where it is needed on the new RAM.

3) Cut the trace indicated by the yellow arrow. This removes the -5V supply to all of the RAM.

4) [This step is optional] Solder the link as shown. This will allow you to use 41256 as well as 4164. This grounds the additional address line (pin 1) on the larger capacity 41256 (this pin is unused on the 4164). With this mod in place you can mix and match 4164 and 41256. The board pictured is running MK4564, TMS4256, and HM50256. There are many more 64k*1 and 256k*1 chips that fit the bill.

Matt Osborn, 2004