Find what drives a dead feature by tracing its lamp
Locate the feature's lamp on the schematic (for example a special-when-lit lamp) and follow its wires back to the relay that switches it. Clean and gap that relay's contacts; that is often the fix.
Systems
Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part Two, Clay Harrell (pinrepair.com)