I just checked mine. At start up, the post shouldn't do anything unless the game started with the post in the up position. If up, the solenoid activates by pulling down toward the ground (switch open) and resets the post down in the cam thing which holds the post down. I think if the cam fails to catch, it will keep plunging because the switch keeps opening on the way up.

If the solenoid activates on game start up, I think the transistor or predriver is shorted (it should pull the post down) or the switch is stuck open. If the solenoid is shorted, it won't activate until the transistor switches the first time during a game (no power to solenoid until then, assuming the mech switch works properly). Per the other comment, if the switch is stuck open and never closes, it would lock the solenoid at start up (game thinks the post is up) and hold it because the switch never closes. Actuate the mech by hand to make sure the CAM engages properly and switch is closed with post down, and open when up. Sometimes these switch blades get damaged or bent which goofs all this stuff up.

I attached a couple pix for reference. Switch closed with the post down.

IMG_0657 (resized).jpg

IMG_0658 (resized).jpg

Just noted, if that switch roller thing is gone on the end of your switch blade, the switch will never close when the mech comes down.

ack! also make sure the switch wiring is intact. This is an open switch if so. This is a violent mech and loose switch and solenoid wires happen all the time.