Testing the CPU board sound section with Leon's sound EPROM

Steps

• The on-board sound section is CPU U24, PIA U9, RAM U23, sound EPROM U21, amplifier U1 and DAC U2.
• Fit the 27128 sound test EPROM at U21 and remove the game ROMs from U26 and U27.
• Power up and check U24 pin 15: it should toggle between 0 and 5 V. If not, check U24 clock and reset, then replace U24.
• Check U9 pins 10-17 toggle (pins 2-9 sit at 0 V). If not, check for a select pulse at U9 pin 23; if present replace U9, if absent check U8: pulses on pins 1-3, only output pin 4 low.
• Press the sound test switch once: U9 outputs should pause and restart, showing U23 is good. If they never restart, check U23 signals and replace U23.
• On a board with no speaker connector 1J15, solder a speaker to the empty 1J15 holes for the test.

Systems

• Williams System 11
• Williams System 11A

Related tips

• CPU sound diagnostic switch SW1 results
• No sound after board work: 1J15 and 1J16 swapped (they aren't keyed)
• Where sound is made on System 9 and System 11/11A
• Setting up Leon's System 11 CPU test EPROM
• No sound from SW1 although sounds play in diagnostics
• Loud constant hum that the volume control does not change
• Sound circuits on the 11A and 11B CPU boards
• Checking ground and +5 V on the CPU board

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)