The game reports a switch 6 (pop bumper) error at the start of a game. It plays fine with the playfield raised but the error returns once the playfield is lowered.

Pop bumper switch error only with the playfield down: weak pop spring

Cause: One pop bumper's return spring was too weak to push the plunger fully back up. With the playfield lowered the plunger rested on the pop bumper switch and held it closed.

Checks

• With the playfield down, watch switch test while pressing and releasing each pop bumper.
• Check that each pop bumper plunger returns fully and does not touch its switch at rest.

Fix

• Re-gap the pop bumper switch so the resting plunger does not close it, or fit a stronger return spring.

Games

• Black Hole

Related tips

• Pop bumpers fire but don't score: bad switch diode on the diode board
• Lower playfield pop bumpers lock on or blow their fuse: shorted driver transistors
• Fuse F21 blows at game start: find the shorted pop bumper driver board
• Black Hole up-kicker on a pop bumper driver board

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