Tuning Judge Dredd for the Locking Ring Mod

The locking ring software is well developed, but requires that your Judge Dredd be working correctly. There are two trouble spots: the ball trough, and the crane mechanism. The planet can also be trouble, but we'll assume that that is working.

The machine here has been through some ham-handed repairs. At some point, it looks like someone pretty good worked on it. However, a later tech just gave up and marked the lockdown bar holder with "3 balls". The crane mechanism has had the typical Judge Dredd wreck where the crane catches on the cabinet when raised or lowered. The swivel rod had been replaced with aluminum, and badly bent. The opto wheels had all been overtightened so that the threads broke out. And there was so much slop in the mechanism that the crane had a hard time working.

The crane is designed with flats on all shafts, so the lever arm eccentric and the crane arm are self-aligning. If all the parts are OK, and the crane is assembled properly - which is simple - it should work. There are two adjustments - the position of the lifter wheel on the crane shaft, and the height of the crane. There are still a few things that can get  you, however. In servicing the crane, your goal is to get the arm motion tight with little slop, and to get the arm positioned over the ball. If the ball clears the plastic, the magnet has enough pull to snap it to its pole. if the plastic interferes, you will get a weak hold and a drop down the front. Arm height is important, and go for a little high rather than a little low. Don't forget to tighten the locknut on the height adjustment.

I have a few key spare parts on Pinbits.

Problem #1 - crane arm collar bracket

This piece fits on top of the swivel shaft. The crane arm mounts to it with a pin, held in by 3/16 e clips. The screw should hold the flat so that the mounting bracket is parallel with the flat on the shaft. The collar is peened onto the bracket.

On this machine, the peened edge is too lose. The crane arm has too much play - you can test this by rotating the crane from side to side. It should not move much. If it does, check that the screw is tight (you will have a set screw). If it still moves, look to see if the bracket is rotating against the collar. I have these on Pinbits, or you can try to stake the two parts together with a hammer. I did best with a replacement part.

That's not the original screw.



Problem #2 - planet slop

These two pictures show how much slop my planet has. The gearbox is worn. I am not going to fix this, the mechanism can accommodate it.





Problem #3 - eccentric and lifter wheel

This wheel lifts the arm, and tells the opto interruptor when the arm is over the magnet. Mine is all busted up, and that clip is a new addition. I have secured a few spares - up on Pinbits.

There is one tuning opportunity. The wheel is set so that, when the crane is fully lowered, the opto is active. This is the point at which the game will activate the magnet. By adjusting the position of the wheel on the shaft, you can set it so that the crane is fully lowered just as the crane reverses its travel. This has the effect of lengthening the time that the magnet carries the ball for. It is an important adjustment, as the carry time is short, and if you are on the wrong side of correct the magnet will drop the ball before it is all the way back. Note that the slot is between the interruptors at 9 o'clock, and the eccentric shaft is at about 11:45.

The eccentric arm wears. That causes slop in the arm movement, which messes up ball drops. My machine was missing its bearing, so I made a new, slightly larger, one out of a bronze sleeve bearing from our local hardware store. (I did eventually find the original in the cabinet). The washer and e-clip are not original. But I feel more comfortable with them on there. I also have the arm on upside down: my new sleeve rides in the worn slot better that way.


Step-by Step Instructions for Adjusting the Lifter Wheel

1) Raise the playfield to vertical and loosen the lifter wheel set screw so that you can rotate it by hand, but so that it stays where you put it.

2) Put the playfield in the down but forward position, so you can reach the wheel behind the backbox - I did this from the left hand side of the machine.

3) Reach down and turn the wheel a fraction. Then use the test mode to run the arm (you'll probably need to go into test 16, and then back to 15). The arm should stop in a different position.

4) Adjust the wheel until the arm stops after it drops, and just starts to rise. This will take a few goes.

5) When you think that it is correct, lower the playfield and run the planet unload test. If that works, secure the set screw and you are done.


The eccentric will straighten up when on its shaft Note the large screw that barely holds the wheel to the shaft. That steel clip is now doing all the work. New parts have a threaded insert and a set screw.




Problem #4 - Upper washer stack

The top side of the shaft is supposed to have a washer and e-ring to hold the arm up. mine did not even have a groove. Here's the new shaft with a PTFE and steel washer.





Problem #5 - Beat-Up Crane

I have had reports of crane arms where the metal is twisted, so that the alignment is off. This problem happens because of the playfield being lifted with the crane caught on the edge of the machine. It also busts up the crane plastic cover. You'll need to hammer and bend to get it straightened out; it cannot be adjusted. 

Here's a movie of the whole thing working.

Note how the ball snaps onto the ring. That snap is the key to a strong hold. Also note how the first two balls are drawn to the magnet: the slop in the ring causes that jump. The third ball is a clean pick. The weight of the balls causes the ring to end up in slightly different positions.