Fuse F9 blows as soon as the game is switched on, even with every output connector unplugged.

Fuse F9 blows at power-up even with all plugs disconnected: shorted bridge BR4

Cause: The bridge rectifier BR4 on the board had shorted.

Checks

• With all plugs off and the fuse still blowing, the fault is on the board itself.
• Test the bridge rectifiers in diode mode; with the board out of the game they are easier to read (in-circuit readings can all look alike).

Fix

• Replace BR4. The spade-terminal bridges Stern used are hard to remove without proper desoldering tools, so consider a repair service if unsure.

Unplug the game before working on the power board; the bridges sit on the transformer secondary supplies.

Systems

• Stern S.A.M.

Games

• CSI: Crime Scene Investigation

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