At power-up there is a loud hum instead of the start-up tone, then a burning smell; the cabinet speaker's voice coil melts. The speaker wires carry DC voltage (about 27 V here) and spark when disconnected.

Loud hum at power-up and the cabinet speaker burns: shorted audio amplifier chip

Cause: The audio power amplifier chip on the sound board had failed with its output shorted to its mounting tab, putting DC on the speaker line.

Checks

• With the speaker disconnected, measure the voltage on the speaker wires: there should be no DC.
• Check the amplifier chip out of circuit.
• Check the electrolytic capacitors in the audio output circuit, which can also be at fault.

Fix

• Replace the audio amplifier chip and the damaged speaker; confirm there is no DC on the speaker wires before reconnecting.

Systems

• WPC Dot Matrix

Games

• Hurricane

Related tips

• No audio output at all from the sound board
• Sound board beep codes at power-on (pre-DCS)
• WPC sound board silent, no power-up bong: try the RAM first
• The WPC sound board runs on its own
• WPC sound board versions
• WPC-89 sound board layout
• Pre-DCS sound board faults by symptom
• WPC-89 resets on low +5 V: replace the small 100 uF 5 V filter caps

Source: Pinball Repair help group!! (Facebook group)