Yes, indeed! One of the more interesting stories from the early days of electronic pinball technology. Stern bought Chicago Coin in 1977 and put out a couple of EM pinballs using Chicago Coin designs. Bally had just started putting out electronic versions of some EM titles using the -17 board-set, and it became apparent that the newly born Stern Electronics Inc would fail unless they could also build electronic games, but they apparently lacked the expertise (or the time) to develop their own design so they basically just reverse-engineered the Bally system, right down to connector compatibility of most boards. In fact if you compare a Bally -17 and Stern MPU-100 board, you will see that the Bally board is obviously designed on a computer CAD system, with perfect/straight copper traces, while the Stern board is clearly hand-drawn with wiggly/curved copper traces. Basically, the Stern engineers traced the Bally design by hand like a child copying a drawing with tracing-paper! It was a ballsy move, and Bally did sue (and won!) but it saved Stern from probable bankruptcy (for a few years, anyways).

As described above, it is relatively easy for a skilled technician to adapt Bally and Stern boards to the "other" format, including the two generations. In principle the MPU-200 board was more sophisticated than Bally boards since it has twice the clock-speed and twice the SRAM.

I'd never heard that: Do you have an online reference for that? I'm a Classic Stern nut, so would love to add to my knowledge of those heady days!

Ah yes, URL (Universal Research Laboratories). The initials show up on some Stern boards. I was aware of the Stern connection, but hadn't heard they were involved in the early Bally boards. I'll have to do some looking on that..