Monthly Archives: December 2012

Star Pool, Williams Pinball Machine (1974)

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Location: Broomfield, Colorado

Symptom: Not powering up, not working.

This pinball machine is located in a youth center in a church basement.  No one seemed to know much about it, other than it was probably donated. So it was unknown when it last worked.

Given the age of the machine, before powering it up, I checked the mechanical operation of all of the steppers and visually checked the contacts on the relays and score motor cams.  Several of the steppers were gummed up, but the rest were in good condition.  I rebuilt the steppers and fixed the left slingshot linkage which was binding.

We had to drill out the lock in the back box because no one had a key and we couldn’t find one in the machine.

Once all of the mechanical parts were working freely, I powered it up.  The machine would get stuck in continuous reset mode.  The reset cycle description in the manual was nearly incomprehensible.  So I was on my own.

I checked all of the obvious things, like the score reels resetting to zero, the ball count stepper unit, player count stepper unit, etc.  Everything was being reset and all reset switches were working.  The only weird thing was the credit stepper was stepping up to the maximum allowed credits during reset, when it should be subtracting 1 credit.

It occurred to me to check the coin switches, which I hadn’t checked earlier.  They were a mess.  I think someone thought they could get freeplay mode by bending all of the contacts together on both coin inputs.  Once I got the switch wires and contacts untangled, the machine would reset properly.

I bent the switch contacts on the credit unit to give free plays.

After that, there was still some minor tuning needed and got 98% of it working well.  I discovered a broken switch contact on the Spinner Advance Stepper (EOS). It was broken right at the insulator which prevented me from soldering another contact on.  I am currently researching a replacement switch or contact.

I will update when this is done.

Red & Teds Road Show, Williams Pinball Machine (1994)

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Location: Broomfield, CO

Symptoms: Delivers too many balls to the shooter lane.

In this era of pinball machine, the ball trough is monitored by infra-red emitters (LEDs) and detectors (photo transistors).  The detectors are on one side of the trough, the emitters on the other side of the trough.  The game senses the ball when it breaks the beam of light between the two.

The owner had suspected faulty opto boards and had replaced them to no avail.

The test diagnostic (“switch edges”) showed that the Trough Jam opto was not working.  It said there was a trough jam all of the time, even when no balls were present.  This caused the firmware to think the ball was jammed and to try shooting it again into the shooter lane.

Switch Matrix (click for larger and clearer)

Even though the owner had replaced the opto boards, I wanted to start at the beginning and make sure it was working. I checked the signal at the collector of the photo transistor while the owner blocked the light in the trough.  When the light was allowed to hit the detector, the collector measured 12 volts (or close to it).   When the light was blocked, it measured near 0 volts.  This is correct.

Photo-transistor schematic; the red dot indicating the measurement point.

At this point, I thought it would be a good idea to check the other switches in the same row and column as the “Trough Jam” to see if there was a wiring or MPU problem in the switch matrix.  Several other switches in the row did not work.

We spent some time tracing the row wire through the various bundles, not an easy task when 40-50 wires are tie-wrapped together.  The row and column wires are daisy-chained from one switch to the next, zig-zagging across the playfield. We found it broken at the White Standup switch.

I re-soldered the wires to the switch and everything worked.

While the switch edges diagnostic was running, we discovered and unrelated intermittent switch.  We found it easily at one of the eddy current sensors because the LED on the sensor board would blink whenever the connection was lost.  One of the wires was pulling out of the connector.  I tie-wrapped the top of the connector to act as a strain relief and hopefully it will hold.