One cannon fires a second or two after the trigger is pulled (the shot sound plays first), and the other drops its ball as it swings toward the flippers.

Cannon fires late or drops its ball: cannons bent downward

Cause: Both cannon barrels had been bent downward. The ball rolled forward in one and upset the cannon's ball opto timing, and fell out of the other.

Checks

• Make sure the newest game ROM is installed (several cannon fixes were in code updates).
• Compare each cannon's angle with photos of a stock game; the ball should sit back in the barrel.

Fix

• Bend the cannons back to their normal angle.

Systems

• WPC DCS

Games

• Star Trek: The Next Generation

Related tips

• Cannons or moving toys work intermittently or won't stop
• Turn ends while a ball is still in play in Final Frontier: flaky trough opto
• Cannon won't turn on the third multiball shot though it tests fine: flaky opto wire
• Deadworld crane sometimes carries the ball back instead of dropping it

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