Working on a Bally Playboy pinball from 1979 today. The problem was interesting… game would start up, play the intro sound, but no ball delivered to the shooter lane. None of the coils worked either.
First checked the playfield 1amp fuse. It’s a likely suspect, but in this case, the fuse was fine. Double checked for 43dc volts at the coils, and there was power. But still, no coils would fire. Going into coil diagnostic test showed no coils firing either.
To understand the problem, we need to know how the game activates a coil. When the game wants to fire a coil, the MPU board sends a 4-bit encoded signal from the MPU board to the Solenoid Driver board (SDB), where the 4-bit are decoded, and the proper coil activated. Also another bit is set high to tell the SDB that a coil is to be fired… This is done because the same encoding is done for the sound board. If the bit is low a sound is activated. If the bit is high, a coil is fired.
This whole process is done through two connectors. One on the MPU board, and one on the SDB. Specifically four wires (bits) plus the control wire (bit) handle this. If one connector pin is damaged (often due to battery corrosion), then the signal received at the SDB is confused, and it tried to fire the wrong coil, or no coil at all.
This is exactly what was happening here. Examining and cleaning/replacing the connector pins at these two connectors got the game working properly!
