They disconnect with a single .156″ Molex connectors, and are easily lost. Instead of doing the power-on flashes, these games have just a faint single power-on «flicker» if the CPU board passed power-on diagnostics. If the board found a problem, then the flash sequence started. The 173 volts AC that is used for the displays is converted to 230 volts DC by four 1N4004 diodes (CR1 to CR4). If there is a AS2518-49 rectifier board, this works identical to the above described AS2518-18 model.
Note the resistor connected between ground and U14 pin 19, the LED board on lamp connector J12 (using the .100″ connector strip at the back of the LED board). Testing the Lamp Outputs.The LED board is connected at J10, J11, J12 and J13, all programmed lamp connectors. Note female connector J1 will have on extra pin that will hang over the edge of the J1 male pins. Bally states, «if there is +5 volt DC and +14 volts DC on the CPU board, the game performs a self-diagnostic test. Power the game on, and again test the voltages to make sure they are Ok. Check the AC Ripple on the Solenoid Driver Board’s C23 Capacitor.Before connecting the J4 connector on the MPU board, check for AC ripple on the solenoid driver board’s big C23 capacitor. This connector supplies power from the power supply to the MPU board. All these parts are available from a pinball retailer.
Lower right corner is the transformer and power supply board. A typical Bally backbox showing all the circuit boards. 1g. Getting Started: Voltage Test Points on the Boards. They used zero-crossing, which occurs 120 times a second for an AC wave (every time the AC wave passes through zero volts). Phase B was wired to zero-crossing detector on the CPU board which generated an NMI interrupt for the 6803 processor. This saves current draw and perhaps a noticeable voltage drop at the transformer.