As soon as the game powers up, the speakers give a very loud, constant hum, loud enough that the game has to be switched off at once. Replacing the two big filter capacitors does not help.
Deafening hum at power-on: cracked ground trace at the DCS sound board filter caps
Cause: On the DCS sound board the two large filter capacitors (C20 and C21) connect to analog ground at header J4 (pins 6 and 7). That trace is fragile and had cracked, often after earlier capacitor work damaged the through-holes.
Checks
- With power off, check continuity from the positive side of C20 and from the negative side of C21 to the analog ground pins at J4.
- One of the two readings will be open if the trace is broken.
Fix
- Solder a jumper wire to restore the ground connection between C20 positive and C21 negative (and ground), following the schematic.
The large filter caps can hold a charge; power off and let them discharge before working on the board.
Systems
Games
Related tips
- Loud foghorn noise at power-on after recapping the DCS sound board: broken through-hole
- 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
- Hum or static that doesn't change with volume: filter caps
- Static or a loud whistle from the speakers
- Line out on DCS and WPC-95 sound boards
Source: Pinball Repair help group!! (Facebook group)