Tag Archives: Bally

Judge Dredd follow up

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Location: Denver, Colorado.

A few months later, I was called back to the Judge Dredd machine mentioned in this previous post.

The thermistor in the power line module had burned out.  I replaced it and tested the machine.  I noticed that the shorted switch-row problem had returned.  The nice thing was, it was a solid failure this time and I was able to track it down.

In my previous post, I mentioned the short would go away if I unplugged J212.  This was the case again, and it deceived me into thinking the short was somewhere along this stretch of wires that heads towards the coin door.   In the switch table in the service manual, Switch 24 is listed as Always Closed.

(The switches and lamps in a pinball machine of this vintage are multiplexed in a grid.  This reduces the complexity of circuitry and wiring.  Rather than having 64 separate wires to 64 switches, by multiplexing, 64 switches can be monitored with just 16 wires.)

Somewhere in the machine, there is a diode connecting Column 2 and Row 4.  It turns out it’s on Coin Door Interface Board, which is were the wires from J212 end up (D2).

What is deceiving is that when a column is shorted to ground, any switch that is closed will show that row to be shorted.  Since switch 24 bridges column 2 and row 4, every switch in row 4 was shown as closed, leading me to believe the problem was in row 4.  But when I closed other switches in column 2, the entire corresponding row would show as closed.  And as a verification, I open the diode at D2 and the remaining switches in row 4 began functioning normally.

Once I determined the problem was actually in column 2, and the symptom indicated it was shorted to ground, I unplugged J205 and J212 to isolate the CPU board from the rest of the machine.  I measured the outputs of each column driver and found the output of U20, pin 17 was stuck at ground.

I replaced the ULN2803 with a new part and everything in the pinball machine tested normal.

 

The Shadow Pinball Machine, Bally/Williams

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Location: Erie, Colorado.

Symptoms:  Neither ball diverter was working, drop targets on mini-playfield were sticking.

The ball diverters at on the left and right ramps were simply loose on their shafts.  I tightened up the set screws on the left diverter.  The right diverter was binding a little after tightening the set screws and I determined the arm was slightly bent.  I straightened it and it worked fine.

Right ramp diverter, with rings on either side. (Photo from ipdb.com)

I removed and cleaned the drop targets from the mini-playfield.  They had been lubricated with white lithium grease, and as usual, it had dried and was causing them to stick.

I looked at the Test Report and it reported that the switch on the main playfield drop target was not working.  It was simply a case of the drop target sticking and never engaging the switch.  I removed and cleaned the drop target.

There were a couple of broken wires that I re-soldered to their correct locations; one was a flasher and the other a GI bulb.  I replaced 24 bad bulbs. There are four rings with lighted jewels incorporated into the playfield (see photo above).  They are illuminated with a grain of rice lamp that is hard-wired.  Three of those lights on this machine are out.  Marco has these and will order.  I’m guessing they are glued in place.

The machine also needs a new set of pinballs.   Any pinballs that don’t look shiny and new should be replaced on any machine in order to keep the playfield in good condition.

All in all, just routine maintenance.

Judge Dredd Pinball Machine (Midway/Bally)

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Location: Denver, CO (Arvada)

Symptoms: Flipper was stuck, multiple connection problems, neither slingshot working.

Stuck flipper: The flipper was stuck because the end of stroke (EOS) switch was broken exactly at the flipper’s maximum travel point.  The flipper wouldn’t return because it was getting hung up on the broken contact.  For a quick fix, I put a piece of shrink tubing over the end of the contact to lengthen it.  As the tubing cooled, I flattened it with my fingers, which basically made a plastic extension for the contact.  Eventually the switch will need to be replaced, but for now it is working fine.

Connection problems:  There were some connection problems causing balls to be continuously delivered to the shooting lane.  Taking a look at the switch test diagnostics, I determined a whole “row” of switches was shorted to ground (row 4).  After checking every switch location in the row on the cabinet and under the playfield, and not seeing any obvious shorts, I decided to look at the back box.  There I discovered if I pressed on the lower corner CPU, the short would go away.  My initial assumption was that it was something on the CPU board shorting out.  Yet, when I unplugged J212 the problem would disappear.

J212

Row 4 is the end pin on the connector (pin 8). So why does lightly pressing on the CPU board cause something associated with J212 to short/unshort.  I looked all around and traced the wires back and couldn’t see anything.  Unfortunately, I moved something and the short went away and never came back while I was at the customer’s site.  After I left the short returned. On a subsequent visit, the problem had gone away again and couldn’t be found.

Slingshots: The owner didn’t realize that neither slingshot was working.  Both had broken mechanical links from the plungers, one had a broken arm.  Replacement parts were ordered and installed.

Doing one last check of the Test Report, I saw that the EOS switch on the left upper flipper was disconnected.  I found the broken wire and resoldered it to the switch.

The Test Report also revealed that one of the ball trough opto switches wasn’t working.  Using a cell phone camera, which can see the infrared light of the opto switches, I determined that one of the IR LED’s was not illuminated.  I checked continuity and didn’t find any problems with the circuit board.  The LED was burned out.  After a discussion with the owner who assured me that the game is working fine, we decided to leave it as is.  There are 7 opto switches monitoring the ball trough and it was of the ones in the middle.  My guess is since the CPU knows it’s bad, it can work around it.  If it causes a problem, there is a very nice after-market IR LED board available which has several design improvements.

And finally, the entire game had intermittent power.  I quickly determined that the line cord was not plugged securely into the rear of the game.

Other than just a few test games, I’ve never played Judge Dredd.  It seems like an interesting and challenging game.

This post has a follow-up here.