With a working unit and a non-working unit side by side testing is easy. You simply move assemblies from on to another and watch the problems recur. The other unit had a bad strobe board. To be sure it was the strobe board and not the main board we swap! We move the strobe unit to the working game and if the strobe still fails it is a problem in the strobe, not the main PCB. For sanity checking I also installed the working strobe unit in the in the other cabinet. That working strobe kept working so it was obviously getting the right signal from the main PCB.

Repeated this procedure for the control panel which had a little stutter in the X axis movement. Same trick for the monitors. Well, more of an extension cable than a physical move, but same testing is achieved.