Dolly – why won’t your switches work for me? – aka the Bally Pinball switch matrix

MPU Pre-Cleaning
U8 image

U8 image

I have been trying to figure out how to address the Bally switch matrix.  I have found (as I have recorded on my issue tracker) that I have 8 switches that aren’t responding.  I looked up how to build the visual diagram of the switch matrix – a grid of 5 columns, and 8 rows.  The first column (0/zero) has switches 1-8, the second column (1/one) has switches 9-16 etc.

I have laid out all the switches based on the game manual and number allocation assigned to each switch – and have determined that 7 of the switches that are out are all on the same column (switches 17, 19-24 – switch 18 is unused), and then switch 34 for a 30point rebound is also out. If this was a Williams game I’d know better how to approach the problem, but Bally addresses the issue of switch management differently – particularly in relation to the matrix.  I know it is handled in one of the two PIA chips (U10 I believe).

I have determined that connector J2 Pin3 is the one that feeds the column.  Now what, not 100% sure :).  I’m guessing I need to make sure I’m getting continuity somewhere else – but haven’t determined that yet.  It is 1am, and I’ve been working on the game for 3+ hours at this point.

Hopefully, one of my great friends will have an idea of how to resolve this.