The left flipper sticks in the up position when the button is pressed and only drops when the game is switched off, so it is electrical rather than mechanical.

Left flipper stays up until power off: faulty flipper board

Cause: A fault on the flipper control board. On these games the flipper EOS switch may have been removed and its wires joined as part of a factory flipper board change, so a jumpered EOS is not necessarily the fault.

Checks

• Turn the power off with the flipper stuck: if it drops, the problem is electrical.
• Check the coil diode orientation against the working flipper and measure the coil.
• Look up the Data East service bulletin about the flipper board modification for mid-1990s games and check whether it has been done.

Fix

• Repair the flipper board (or apply the bulletin's modification), or fit a replacement flipper board.

Systems

• Data East CPU Version 3

Games

• Jurassic Park

Related tips

• Flipper sometimes stays up until power off: broken coil diode
• Upper flipper dead and its flipper board LED never lights: dirty cabinet button switch
• Solid state flipper goes up but will not stay up
• Flipper stuck up with power on (Playboy and later)
• Solid state flipper stays up only after the button is first pressed
• Flipper board LEDs show the cabinet buttons are seen
• Flippers die after being held a few seconds, then recover
• Solid state flipper has no power though fuses are good

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