The hardware that runs the classic Bally/Stern series of pinball machines is by far the most prolific of all the pinball systems. Consequently there are tens or even hundreds of thousands of these machines still out there. Many in need of repair. Over the years I’ve grown to know this hardware quite well and currently I’m working on some new hardware designs for use with this system.

One of the projects I’m working on is a daughter board to replace all of the RAM and ROM on the MPU board with a new board that connects to the J5 test connector on Bally/Stern MPUs. The board I’m covering in this article replaces the ROM only and uses two 2732 EPROMs. This is a proof of concept for a future design that will use a 2764 (or 128, 256, etc…) and an NVRAM.

My main intent with these boards was to be used as a test aid with Leon’s test ROM but they also work well to simply replace the EPROMs. This is especially useful on MPUs that are strapped for 9316 ROMs. I liked these boards so much that I designed a slightly nicer version with a couple more LEDs that I’m going to produce intended strictly for testing.

Here we see the board in action:

This picture shows the board being bench tested.

I didn’t get a lot of these boards made on my last board run because it was mainly a proof of concept but I was able to sell a few to other collectors. I will run quite a few more of the next version. I know I would want one if I hadn’t built them!

This box is my “problematic MPUs” box. Most of these either have 9316 ROMs, bad sockets or some other problem that makes them a pain to test. I ran through this box of MPUs in about an hour with my daughter board. I didn’t fix anything but I was able to test the CPU/Clock on all of them and I got most of them to boot (some with manual reset).

The next version will be even cooler! Stay tuned…