Quick Draw Pinball Machine, Gottlieb 1975

Location: Fort Collins, Colorado.
Symptoms: Score reels sticking, not resetting, 50 and 500 points items not scoring, not always advancing to next player or ball, bonus countdown issues, score accumulating when switching players.

The machine has been missing the rear door for the backbox for a long time and a lot of dust had settled in there.  The switch contacts on the player unit needed cleaning and adjusting.  This accomplished a lot in eliminating problems. The score advancing when changing players was due to the reset contacts (switch stacks P3 and P4) vibrating or set too close.

The player unit keeps track of ball numbers, player turns, and controls the reset of the scores. What makes working on the player units difficult is that the switch stacks are very close together. I’ve made a home-made switch adjusting tool that is able to fit in between switch stacks. I’ve also made some cleaning strips with a jogged shape them to help with switch cleaning.

Some of the decagon units needed to be rebuilt and contacts cleaned. A majority of the time was spent in the backbox.  The owner will craft a new back door to help keep the dust out.

There were a few other mis-adjusted contacts on the bonus unit and the 50 and 500 point relays.

Another EM pinball machine saved.

Close Encounters of the Third Kind Pinball Machine (EM version), Gottlieb (1978)

Location: Parker, Colorado.
Symptoms: Machine not resetting, points not registering, drop targets not resetting, bad light socket, and various other problems.

This is the rarer electro-mechanical version of this pinball machine.

On most EM machines, you can disconnect the credit subtract coil to put the game in Free Play mode.  However, on this machine, there are switch contacts on the credit subtract lever that trigger the Start Relay (S). I bypassed those with a wire.

Next, the relay coil spring on the Reset Relay (AX) had been previously replaced with the wrong one that was much weaker.  I traded the spring from the Hold Relay, where the spring tension is less critical, to the Reset Relay and then re-adjusted the contacts. This fixed the problem with the machine not resetting correctly.

Next, many of the point scoring relays such as the 500 point and 5000 point were not holding though a cycle of the score motor.  They are all common and routed through the normally closed Motor 2B switch.  This switch was simply out of adjustment.

Eight relays are routed through a common hold switch on the score motor.

Eight relays are routed through a common hold switch on the score motor.

One of the formed switch blades had broken off the score motor and a replacement was obtained from The Pinball Resource.

Broken formed switch blade from Score motor.

Broken formed switch blade from Score motor.

Some of the contacts on the player unit needed to be cleaned and adjusted, which is a typical problem with Gottlieb multi-player machines. The bonus stepper unit was gummed up and not advancing or awarding bonus.  It was cleaned and rebuilt.

The spinner switch needed adjusting because it was scoring points with just vibration from the playfield.

After replacing a broken light socket and spraying the back side of the backglass with Krylon Triple Thick Clear Glaze (to help stabilize the paint and keep it from peeling), the machine was looking and working great!


Silverball Mania Pinball Machine (Bally, 1980)

Location: Arvada, CO
Symptoms: Blows playfield coil fuses; needs new rubbers and bulbs, cleaning.

I started by replacing both playfield fuses since they were blown.  When I started a game, the kicker at the outhole started firing randomly, sometimes very rapidly.  The sensing switch seemed to be fine. I also noticed that some of the pop bumpers weren’t firing correctly.  If I pressed on the left pop bumper skirt, the center pop bumper would fire.  Basically there was something not right with the solenoid driver circuit.

I started with the signal for the kicker coil, and with the oscilloscope, I traced it back through the solenoid driver board. The signal going into driver transistor Q11 was going crazy.  I went further back to the output of the 74154 decoder chip (U2) and the signal (pin 15) was still crazy and random looking. No wonder the fuses blew.

I checked the input signals to the 74154 and the “B” signal was randomly moving between 1 and 2 volts.  This is neither a digital “1” or “0” and it makes digital circuits act randomly.  I traced the signal further back to the MPU board to the output of the 6820 PIA (U11, Pin 11).  Since the 6820 was already in a socket, I lifted it out of the socket and bent pin 11 out, then put the 6820 back in.  This isolated pin 11 from the rest of the circuit to make sure that nothing else was interfering with the signal.  The oscilloscope showed it was still bad.

6820 PIA chip with pin 11 lifted to isolate it from the rest of the circuit.

6820 PIA chip with pin 11 lifted to isolate it from the rest of the circuit.

The faulty “B” signal would also cause the wrong pop bumpers (and other solenoids) to fire.

I replaced the 6820 with a 6821 (they are interchangeable)  Also, I replaced the 5101 RAM chip on the MPU board with an AnyPin NVRAM module and removed the battery from the circuit board. This will save the MPU board from future corrosion caused by battery gasses.

At this point the machine was working well, except it wouldn’t boot about 50% of the time.  It looked like a problem with the reset circuit.  Bally didn’t include a time delay in the reset circuit like most other manufacturers. I added a 4.7 uF tantalum capacitor across R2 to give the reset a little bit of time delay when it boots.  It solved the problem and booted 100% of the time after that.

4.7uF capacitor added across R2 to assist reset circuit.  AnyPin NVRAM module in lower right.

4.7uF capacitor added across R2 to assist reset circuit. The positive pin of the capacitor is connected to the right side of R2.  AnyPin NVRAM module in lower right.

Finally, all of the rubbers were replaced, bad bulbs replaced, and the playfield cleaned and waxed. Some of the light sockets needed cleaning because the bulbs weren’t making good connections.