Lots of static, or a loud steady whistle from power-on that the volume control doesn't change (seen on Jack*Bot).

Static or a loud whistle from the speakers

Cause: A failed TL084 op-amp, a TDA2030A amp (DCS and WPC-95), or the large filter caps or their cracked solder joints.

Checks

• Unplug the sound board ribbon and remove the sound EPROM. If the noise continues, the fault is in the amplifier stage, not sound processing.
• Test the TL084s and TDA2030As.

Fix

• Replace the failed op-amp or amp (a TL084 in the Jack*Bot case).
• Reflow or jumper the large filter capacitors.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Games

• Jack•Bot

Related tips

• Deafening hum at power-on: cracked ground trace at the DCS sound board filter caps
• Loud hum at power-up and the cabinet speaker burns: shorted audio amplifier chip

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Three, Clay Harrell (pinrepair.com)