All flippers are weak or sometimes dead when worked with the cabinet flipper buttons, but work perfectly from the handle triggers. In switch test the button switches register only now and then.

Flippers weak from the buttons but fine from the triggers: opto board headers

Cause: Poor connections at the cabinet flipper opto boards (worn header pins and tired solder joints).

Checks

• Hold each flipper button in switch test and watch for flutter.
• Clean the optos, then inspect the opto board header pins and solder joints.

Fix

• Replace the header pins on the flipper opto boards and reflow the solder on the boards; repin the matching connectors too.

Systems

• WPC DCS

Games

• Demolition Man

Related tips

• Weak or dead flippers from failing LM339s on the Fliptronics board
• One flipper dead and its button fails switch test: dirty flipper button opto board
• Fliptronic flipper dead though the button reads
• Fliptronics: flipper button does not register in switch test
• Flipper dead because the Type 2 plastic interrupter warped
• Checking flipper buttons and EOS switches in switch test
• Fliptronics flipper does not work: test the flipper opto board
• Fliptronic flipper dead: check the button first

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