Jurassic Park: T-Rex Jaw No Longer Working

Fatsquatch

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Well, I finally got my JP last night, and I'm excited to report that the machine looks even better in-person than it did in the auction listing. The legs drastically need to be repainted and the cabinet has it's share of little nicks and scrapes, but other than that, this machine is really nice. (The playfield is damn-near perfect.) And most happily, the game is fully working.

As was advertised, the T-Rex left-to-ride movement is about gone. Since I don't find that to be that big of a deal, I just disabled the L-to-R movement. After that, the T-Rex did fine for a few games, and then the jaw just stopped working. When it WAS working, it never looked sluggish or anything, and seemed to be in good shape. The T-Rex still drops down over the ball, but the jaw doesn't move even the slightest bit. (The jaw isn't working during the diagnostic mode either.)

Can somebody give me a protip as to what I should check on to straighten this out?
 
you need to go through the switch test and make sure all the switchs are working as should there different points where it stops .this is desibed in a manual.on mine when i had it i had to bend like the front teeth a little he always droped the ball.i think this may be in a service old bullitian
 
Now the T-Rex doesn't even go up and down; he just doesn't move at all. On startup, all I get is a "tick-a tick-a tick-a" kinda sound during the T-Rex diagnostic.

I'll run through the switch test as suggested and see if that tells me anything. Thanks!

(I'd refer to the manual, but I don't have one. :( )
 
IPDB has a manual, so get over there and download it.

T-Rex is a tempermental beast.
First make sure that you have the latest ROMS in there, Marco lists the Game ROM as 5.13, and the display as 5.10. The later versions of the ROMS changed how the computer controlled T-Rex and the changes extended the life of the motors.

There are three motions to T-Rex, L-R, Up-Down, and Jaw.

The Jaw is a solenoid. The wires going to the jaw get bent every time T-Rex bends over to pick up the ball. If the wires are not installed correctly, or are rubbing they will break.

Up-Down, is a motor, and two switches for position. T-Rex will only bend down if the center(L-R) switch is activated. If T-Rex does not bend over, make sure that he is centered and the center switch is active, it may need adjustment.

L-R is also a motor and three switches, Left, Right, and Center. The left and right are used to stop the motion, and the Center switch tells T-Rex that he can bend over for the ball. The most common issue with this is that the direction relay has bad solder joints and that causes T-Rex to move one direction and not return. The relay board is located under the playfield near the flippers, follow the wires, it is pretty easy to find.

Fortunately there is a good diagnostic routine for T-Rex in the Diagnostics menu. The diagnostics control all of the functions and display all of the states of the switches. That will help you locate the issues.

Mike
(on my second JP)
 
I totally forgot about IPDB having manuals. Thx!

When I went into diagnostics, the up & down started working again, and has been working in-game ever since. *shrugs*

To check the wiring trouble-spot for the jaw, do I need to look underneath the T-Rex or inside of him?
 
I totally forgot about IPDB having manuals. Thx!

When I went into diagnostics, the up & down started working again, and has been working in-game ever since. *shrugs*

To check the wiring trouble-spot for the jaw, do I need to look underneath the T-Rex or inside of him?

Probably wasn't centered, diagnostics got him centered, and then he started working.

The wiring trouble spot is inside of him. Best way to get there is to remove the entire assembly, then take him apart.
 
Thanks, Ken. I'll add those PDFs to my collection.

From a visual inspection, the wiring to jaw's coil looks okay. The wiring at the coil wasn't loose (I reflowed it anyways), and there are no naked areas along the length of both wires. Tapping the black wire at the coil's solder joint with my soldering iron causes the coil to kick, so the coil itself isn't dead.

Reckon' I have a bad piece of wiring that simply can't be seen? Possible bad diode on the jaw's coil?
 
The manual page 31 shows a BRN-GRN wire going to the Dino Mouth Solenoid from Q26

Thanks! Sounds like this loose wire is definitely my problem.

I see what you're talking about on the page in the manual, now I just have to make sense of the diagram as it relates to actually restoring the wire to its original home. ;)
 
Thanks! Sounds like this loose wire is definitely my problem.

I see what you're talking about on the page in the manual, now I just have to make sense of the diagram as it relates to actually restoring the wire to its original home. ;)

It is the side of the diode without the line. The other end is on the CPU board CN12 pin 8. Another picture in the manual is on page 48 in the bottom left corner.
 
Ahhh, I think I gotcha.

I need to restore the loose wire to the connector that holds the black & white wires that run directly to the jaw's solenoid. And while doing so, making sure to connect it to the wire that runs to the end of the solenoid's diode that has no line on it.

A million thanks!
 
Thanks again, Geese. The T-Rex is now chomping pinballs once again. :)

Except for missing the topper, my JP is now 100%.

What a seriously fun game this is. Woohoo!
 
Thanks again, Geese. The T-Rex is now chomping pinballs once again. :)

Except for missing the topper, my JP is now 100%.

What a seriously fun game this is. Woohoo!

Glad I could help.

There was a topper that just sold for $56 on Ebay. Marco Used to have them for $79. They seem to be getting scarce again. Good luck finding one, I am looking too.
 
I was bidding on that one, but got sidetracked and didn't make it back to the computer in time to bid against the end-of-auction snipers. :-(
 
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