Well I found some time and pulled the DRAM bus termination resistors from one of my rev 0 replicas, to see what would happen. I expected to find the machine still worked but with some erratic behavior. I planned to take before and after O’scope shots of the DRAM address bus to be able to demonstrate the difference.

What I expected and what I got were quite different. What I got, was a machine that wouldn’t boot and give me a monitor prompt at all. I couldn’t really do before and after O’scope images, because I couldn’t generate an apples to apples comparison without putting the processor into the same tight loop for both test cases. However the display on the video was stable, so it shows that DRAM access was at least mostly working without the termination resistors.

I tried 4K and 36K DRAM configurations, and found no difference in behavior.

While my reproduction isn’t an original Apple preproduction board, I don’t think behavior would have been significantly different on a preproduction Apple II.

Just to speculate a little. There may have been enough board to board variation that some pre-production units worked better than others, but I imagine that on the whole, things didn’t look very promising when the first prototype Apple IIs were built. Imagine the struggle that the early Apple employees had, finding a way to stabilize the computer enough to show at the West Coast Computer Faire, and more importantly get it in shape for revenue shipments.