check if yours is one of the early games prior to 87012. There is a service bulletin for this game specifically for the t-rex. There is a article on it in playmeter magazine.

Also check if you have the latest code [rom revision 5 i believe]. it helps with the dino operation. Could be binding and not operating right in game and work in test. Switches can be flaky.

Sometimes when operated slowly after not working for a game or 2 they become sticky internally and do not actuate correctly until the second time.

I found my T-Rex had trouble eating the ball when the game was not level.

Make sure the scoop the ball sits in isn't cracked or broken. Mine was cracked and she would drop the ball, got a new one and has worked ever since.

If he does a LATE Chomp only on the way up I had the same problem.

Take him apart and look at the wiring. Most likely after all that up and down the wire has broken in half and is only touching when in the upright position.
I cut each side and soldered a new in between wire with more slack.

works perfect now.

Yup agreed. Check wires, and if you want you can upgrade them to a more multistranded wire. Great for things like this but not cheap.

Oh yea.The JP article was in the vol 19 august 1993 PlayMeter mag. Check it out jurassic owners. neat read. Has great picture with Gary Stern in the egg room wth the cast of JP in the main article besides the dino update.

Its not that hard. Turn the machine on and then off wjen the trex lowers. Then remove the plastic playfield collar , thwn the back of Trex ( just one screw ).
Then trace the wire and consider splitting the casing to check the black and white wires at the bend point.
My white wire was broken and when i fixed it now works great. Good luck

Looks like the yellow saucer is cracked. Replace that and try to play it again. The dino will not act right if that saucer is damaged.

I will scan the pages from the magazine when I get a chance. I am looking right at the Magazine right now.

also make sure any screws are in and tight the way they should be.

the ball will not sit right or get pressed down or what have you. I cannot see how bad yours actually is but from the pic it looks cracked and may be hampering operation.
If its cracked it needs to be replaced anyways so no harm done.

I'm having the same issue. T-rex begins to raise, then chomps. He has raised about 1/8" to 1/4" when the chomp happens so he just knocks the ball out of the hole.

again switch adjustment is key. Plus as switches age the sweet spot changes and takes longer to activate and reset for another operation. Could be yours are just old and need replacement.

But adjusment is paramount. Once its done it works flawlessly. great design. But our favourite games are getting on in age friends.

how well does your saucer switch work? Check that bad boy. If its flaky it will forget the ball is in the saucer and not chomp.

Maybe try switch test and bang on the middle of the playfield and see if any flake out. or any double switch activations or any weirdness at all and report back.

Just clean everything and maybe the slightest wipe of grease on metal to metal contact points only. NO WD! . get synthetic grease. Great stuff. never goes bad.

You can usually 'feel' a switch is bad when operated with your finger. It is very unlikely all your switches are bad. Not impossible...just unlikely

Even though I don't think it's your problem:

https://www.marcospecialties.com/control/keywordsearch?SEARCH_STRING=eject+shield

no but he needs it anyways from the look of his. I think its a switch issue for sure.

And here's how to remove the tabs, https://pinside.com/pinball/forum/topic/jurassic-park-restoration/page/9#post-4149188. No one sells them without the tabs anymore.

Mine didnt seem cracked very bad either (if i recall it looked a lot like yours) but it was enough to keep the ball from sitting up high enough for the rex to grab it.
It always amazes me how something being the smallest bit out of adjustment can change the way a game plays.

Rex grabs the ball, brings it up then swallows, and chomps at the top after swallowing the ball.

If you want to try a quick test with the saucer before buying a new one, switch the TRex saucer plastic with the one in the top right in the Boat Dock. Same part.

Found this in the manual, so it looks like it does turn in both directions.

trex motor (resized).JPG

Found the problem on ours. It was the classic broken wire in the harness. I figured it out by using the t-rex test mode. The jaw would snap perfectly in every position except all the way down. As soon as t-rex moved up just a fraction of an inch the jaw would start working again. I just spliced in a 1 inch piece of stranded wire, soldered it and wrapped it up in electrical tape. Works perfect now!

Yep. Classic issue. I had to run a new wire that bypassed the tubing that the wires run in.

That's a diagram of the left/right motor and bi-directional relay for it.

The only motor that is bi-directional is the left/right motor. The up/down motor should only be turning one direction. The movement in that one direction makes the t-rex go down and up.

Oh, good catch. That does make more sense!