The coffin lock's sense circuit reacts when the ball arrives but the magnet never grabs it. On heavily played games the magnet fuse may also blow at random.

Coffin magnet senses the ball but won't grab it: burnt resistor on the magnet board

Cause: The 160 ohm 5 W resistor on the magnet control board runs too hot for its rating. It had overheated, cracked and drifted far off value.

Checks

• Look at the large power resistor on the magnet board for scorching or cracks.
• Measure it out of circuit and compare with its marked value.

Fix

• Replace it with a 150 ohm 10 W resistor; the board's silkscreen has room for the larger part.
• If magnet fuses keep blowing, consider the updated magnets (090-5042-00) with better thermistors.

Systems

• Stern S.A.M.

Games

• Metallica (LE)
• Metallica (Premium)

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