Building a custom micro-controller for early Bally/Stern solid state pinball machines

This is an introduction to an up-and-coming technology that a small group of pinball and electronics enthusiasts are developing. A custom microcontroller that interfaces with Bally-35 MPUs and allows you to write customized rulesets, even completely re-theming games. This is the first part of a journey that I hope to take everybody on.

NOTE: This is a video I recorded several months ago that I forgot to make public, so I’m much further along.. But thought it might be interesting to show this early look at the development of this technology. Now there are etched boards that can be acquired.

Recommended mods to Bally-18/35 and Stern solenoid driver boards

In today’s episode, I go over some standard, recommended modifications to the Bally-35 series solenoid driver board. There are over 60 popular pinball games that use this hardware setup and these quick modifications will help make the game run better and more-reliably. They involve adding three jumpers to the board. Whenever I have a chance to work on one of these boards, I do these mods.

Here are some front and back pictures of both Bally and Stern Solenoid driver boards. The black wires are the mods. The other colored wires are done by operators having to do with the coil lockout relay.

Bally Solenoid Driver board
Stern Solenoid Driver Board

Work continues on the Bally Mr. & Mrs Pac Man Pinball Game

In the continued saga of bringing this 1980s game back to life, I begin to go over the electronics and figure out why the game wouldn’t boot up.  Normally you fire up these Bally machines and count the number of times the LED on the MPU board blinks, but in this case, the game didn’t even get far enough to begin to start up the MPU.  Fuse F3 kept blowing and the game wouldn’t power up at all…

An examination of the schematics showed an area on the power rectifier board where it was likely some components were damaged and needed to be replace.  Luckily, these were not very obscure items so I could pick them up easily.

Stay tuned for the next installment where I go into addressing an issue with a broken plastic rail guide that probably can’t easily be replaced, so I have to fabricate my own!

 

Fixing a dead dot matrix display board

The other day the DMD just went “poof” on one of my machines.  After doing a little research, and checking connections and things, I realized the DMD board died.  In this installment, I walk through the process of rebuilding the power supply-portion of a Bally/Williams WPC DMD board.  In part 1 I describe what I’m doing and introduce you to the tools I’m using.

 

Next up, let’s talk about using a meter to check circuit board traces as we go along..

Desoldering and replacing components.

Now the moment of truth!  One thing I want to add is pay very close attention to each item you are replacing on these boards.  Two diodes, capacitors or transistors may look alike, but have slightly different values or part #s.  The three power transistors and the diodes are not all the same.  You may have to bust out a magnifying glass to note the different in the markings on each part.  This should also be cross-referenced with the schematics and/or parts list from the game manual.