I know that this issue has been gone through several time in "usual places" but I haven't found solution to my problem. My Cue Ball Wizard has issues with switch/light-matrixes, no life at all. When I boot up game, it goes to attraction mode nicely but that's about it. I can go to menu with that yellow button but that is only button that works. I have fixed similiar problem at one other Sys3 with changing MPU-board but now I'm stuck. I have 2 MPU-boards but either one works correctly. Driver board has almost all transistors replaced (originals were those BUZZ72's) and it's working ok (tested with that previous sys3 game). I have replaced U11 chip (display was garbage before that), dallas-chip is like new so no acid damage (now it has battery holder). Jumpers for eprom are correct. I have manual if you need some details from schematics etc., just let me know. Oh, forgot, flippers has power, some point at menu I'm able to flip those. Also flashers works fine (at test). Tournament mode-switch is not doing anything. And fuses are ok, double checked and changed F6 just in case.

Anyone? There is a ton of messages about sys3 boot problems with exact same symptoms, game boots, all backbox leds blinks, display is fine but all cpu-controlled lights are out and switch matrix is dead. Only test, slam and tilt switches works. It's like driver borad is not getting fire-commands from cpu. Ram/rom/cpu-problem? Some buffer-chip dead?

Still valid issue. I got U3-ROM chip replaced, no help. Next I'll attack to U4/U5 VIA-chips. But is there a way to determine where signal is lost or is it not coming from CPU-chip U1 at all. Logic-probe or oscillator are available, just need some info about usage

Also checked U10/U11 from driver board that voltages were fine, so those should be able to strobe switch-/lamp matrixes. I'm still little confused about this "Master Reset-signal (MR)" that is mentioned on "Theory of operation" part of manual. What generates this signal, how I can be sure that it's not on?

Solution found, it was indeed bad ribbon cable.

Yes, it was indeed ribbon between MPU and driver board.