I'm stumped... my Williams Stellar Wars (system 4) has a matrix issue and nothing seems to be fixing it.

What happens:
The W rollover sometimes, but not always, resets the left target bank. The top and middle drops on the left target bank do not score. The lower target always scores and always reset the bank regardless if the other two targets are down.

What I've done:
1. Replaced and socketed all ICs that are part of the matrix circuit
2. Replaced the 40 pin interboard connecter
3. Tested every switch diode for open or short
4. Tested every row and column for short
5. Removed, cleaned, adjusted and re-assembled all targets banks (including the pcb traces and switch contacts)
6. Manipulated many wires and harnesses looking to find a wire short that might activate a switch
7. Removed and re-seated all ROMs

None of the above has altered or changed the symptoms at all. I think one of the drops has scored a couple times before but so rarely, and after so many run throughs, that I'm not sure I believe it happened anymore. These switches share a column or row but not all are on the same column or row. Illustration attached...

Any ideas?

[att=743894 caption="image_(resized).jpeg"]

image_(resized).jpeg

I did not run that specific test... but I'll try it and see. 4 was me testing for shorts in the wiring by buzzing out the matrix rows and columns.

As expected, the problem was in the cab. Seems a previous owner, or the factory, installed the target PCBs upside down and backwards. I bought it with this matrix issue and took pics before I took it apart and never noticed that these boards were installed differently than the others. Live and learn... thanks for helping talk me through it. Every pin is a new lesson it seems!