The clock runs normally with the playfield up in service position but stops or loses its place once the playfield is lowered.

Clock works with the playfield raised but fails when it is lowered

Cause: A faulty clock board. One member notes that some reproduction clock boards mount the optos differently, so when the playfield is down the minute hand can sag forward and miss the 12 o'clock opto.

Checks

• Make sure the two small connectors on the bottom of the clock are firmly seated.
• In switch test, watch the clock optos while lowering the playfield.
• Check whether the minute hand fully breaks the 12 o'clock opto beam with the playfield down.

Fix

• Replace the clock board if the optos drop out with the playfield down and wiring checks out.

Systems

• WPC Fliptronics

Games

• Twilight Zone

Related tips

• Clock minute optos miss now and then: repin the plug at the 10-opto board

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