Hi,

During gameplay, the T-Rex is not always centered. Does it move perfectly during test mode ? Also, regarding the movement, if you have the latest ROM 5.13, the movement is not smooth. The motor is given small impulse instead of constant current. You can always upload a video and I could tell you if it behaves like mine.

Marc

My T-Rex was moving only one side when I got it (like yours). In my case, the problem was Q27, the transistor that drives the relay under the playfield.

If your T-Rex moves properly in test mode, that should not be the problem. If it does not, the first thing I would do is check the solder joints on this relay boardIMG_0880.JPG. If you have some TIP122 (or TIP102), I would replace Q27 to take this out of the equation.

When the relay is switching, we can hear it. You can disconnect the connector that is going to your motor (blue wires) so that you can perform your tests without moving the t-rex itself.

Good luck !

Marc

Q27 drives the relay so if there is no power on your motor, this is probably not your problem. As you mentioned, you can try to power the motor itself with a battery. You can also check with your DMM if there is some power on the motor connector (the one with 2 blu wires). Close your pinball door while you are doing your tests but be really careful. When the door is opened, the high voltage is disabled.

The motor itself is driven by the Q24 transistor on the MPU. Q27 drives the relay that switches the polarity on the motor. Long story short, if there is no power going to your motor, you might have burned Q24.

There is also a fuse (F1) on the shaker motor board that provides voltage to the left right motor. It could also be burned. It's worth taking a look.

There are some more explanation in this Stern service bulletin.

http://files.flipperspill.no/Support/Pinball/Serviceb/Stern/039A_SB.PDF

Nice ! Easy fix in the end. It's good to know how the T-Rex works anyway