Right after the sound board was recapped, a loud foghorn-like tone blasts as soon as the game is switched on. A spare sound board works normally.

Loud foghorn noise at power-on after recapping the DCS sound board: broken through-hole

Cause: Removing one of the large filter capacitors broke the plated through-hole under it, so one side of the cap is no longer connected to the trace on the other side of the board.

Checks

• Switch off at once to protect the speakers.
• Compare continuity from each large filter cap's leads to the traces and header pins on both sides of the board, against a good board if you have one.

Fix

• Repair the broken through-hole with a solder stitch (a short wire through the hole soldered on both sides).

Systems

• WPC-Security (WPC-S)
• WPC DCS

Games

• The Shadow

Related tips

• Deafening hum at power-on: cracked ground trace at the DCS sound board filter caps
• Sound cuts out or a rising shriek after a few minutes
• Sound board beep codes, WPC-DCS and WPC-S
• DCS or WPC-95 sound faults: amps and op-amps
• All sound stops when a game starts, two error tones at boot: reseat CPU chips
• Line out on DCS and WPC-95 sound boards

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