Twilight Zone
Game Information
| Manufacturer | System | Year | Model | Produced |
|---|---|---|---|---|
| Bally | WPC-Fliptronics | 1993 | 50020 | 15,235 |
IPDB Link (including software and schematics)
Twilight Zone Playing Tips and Rule Sheet
Game-Specific Issues
Upper Left Flipper Doesn't Work During LITZ or Powerball Mania
A game adjustment turns off the upper left flipper during certain game modes. This setting should normally be set to "No". Note that while the manual indicates both flippers will be disabled, only the upper left flipper is disabled.
Powerball detection
How does Twilight Zone keep track of where the powerball is?
Twilight Zone has two eddy sensors to sense magnetic balls. One is at the ball eject position in the ball trough. The other is located on the under playfield tunnel that feeds balls from the piano, gumball, camera and deadend holes back to the slot machine eject.
The under playfield sensor is rarely a problem but the trough eddy sensor is one of the worst problems in the game, second only to the clock. If the machine is having trouble keeping track of where the powerball is, it's probably due to a problem with the trough eddy sensor.
The machine discovers the location of the powerball by using a combination of four different methods:
- By using the eddy sensor in the under playfield tunnel. If a ball triggers the piano, camera or dead end switches and then the slot switch triggers *but* the eddy wasn't triggered in between, then we know the powerball must have gone through.
- By using the eddy sensor in the ball trough
- By failing to grab a ball successfully on the loop magnets.
- By counting the powerball as it goes in and out of containers during single ball play, such as the lock, gumball and trough.
So for example if the machine knows there's two balls in the trough and you drained the powerball during single ball play, it'll be out the trough again in 2 balls time. By doing this it's possible for the software to work around broken/failing eddy sensors.
Typical problems
- Machine says "Powerball" when the powerball is not in play or vice versa
- A credit dot with a "Switch 26" error.
Causes
Connector Spring Failure
The trough eddy board and its sensor are joined by a small cable. With the vibration from the trough, the brass connector pins lose spring and the connection becomes unreliable. There are two solutions. You can solder the wires directly to the boards, or you can buy or make a new cable.
Cracked / Bad Solder Joints on Sensor
The following applies if trough detection problems of the poweball persist, even after the leads of the trough sensor board (WMS / BLY technically refers to it as an A-16528 "Trough Coil Assembly"), have been directly soldered or replaced. Carefully inspect the four solder leads where the sensor is soldered to the board. Due to vibration, the solder joints can become cracked, and cause the sensor to sporadically detect the powerball.
Damaged Sensor
The sensor is adjustable, and needs to be within 1/16 of the ball to work. If it is too close, the ball hits it and destroys the plastic. If it gets to the wire, the sensor will permanently fail. Although the sensor may look beaten up, the problem is still usually the cable.
Out of Tune Circuit
The design doesn't accommodate all variations of parts and conditions, and may end up being too robust and never respond to a close ball - or it may never start up. One fix to try for a stuck red light is to add some twists to the cable, although be careful as the cables/connectors are known to fail easily.
There are two modifications suggested to allow adjustment to the circuit allowing it to be "tuned in" with more accuracy. The first, suggested on http://www.actionpinball.com/tech/tz_prox.htm is bogus and does not work except by accident as suggested by Kenny McCormick. Undertaking this modification will not help the circuit to function. He further suggests a modification replacing the 2.2K ohm R1 resistor with a 20K ohm potentiometer. https://groups.google.com/forum/#!topic/rec.games.pinball/1cvD4hZO9E0
Recommended is removing R1 and replacing with a 10K ohm pot in series with a 1K ohm resistor (1/4w). The 1K ohm resistor acts to prevent the pot from being adjusted to a dead short. One of the end leads of the pot is left unused and clipped off, the other is placed in one of the vacated R1 PCB holes The middle connection of the pot goes to one end of the 1K ohm resistor the other end of the 1K ohm resistor is placed in the other vacated hole of R1. This completes the modification, the board is then reinstalled and the pot adjusted so the LED just goes out with no metal ball in proximity. The LED ought to then light when a ball is placed in the trough.
Failed Optocoupler Output
The output signal is driven by an optocoupler across the switch matrix. A short to the switch matrix can destroy the optocoupler transistor. Replace the optocoupler if the LED works correctly but there is no switch signal.
The Clock Mechansim
The Twilight Zone clock is both undeniably awesome and a bit of a troublesome feature of the machine.
Clock reliability is impacted by three original design features:
- Excessive heat generated inside the clock by the four #86 lamps
- Special optos (QVE11233.0086) required to guarantee reliable operation
- The sandwiched two-board design requiring bottom entry .100 connectors
The first problem with the clock is that it overheats. About half the heat comes from the incandescent bulbs, which generate 4.8W. The balance comes from the opto emitter circuits, which generate a total of about 4W of heat (8 * 40mA* 12V). The clock enclosure becomes hot. The opto emitter current limiting resistors get hot enough to burn the board. Finally, the clock case yellows more quickly.
Aftermarket clock boards generally use LEDs in lieu of incandescent bulbs, greatly reducing heat inside the clock enclosure. The challenge remains to identify optos that can work properly when connected directly to the switch matrix.
Note: A problematic clock can be turned off in the game settings.
Testing the Clock
Twilight Zone game software includes a specific test for the clock.
The clock test can run the clock forward/backward both fast/slow. While the clock motor runs, the status of each of the 8 optos is reported. If during the test, any opto reports bad, then the test will stop.
A YouTube video, showing properly working clock behavior at power on can be found here.
A YouTube video, showing a working clock in test can be found here.
Replacing the Optos
Williams used specially selected optos that were capable of driving the switch matrix. These parts are labeled QVE11233.0086 and are long since obsolete. A commonly used replacement is the OPB804, but this part really doesn't meet the original design spec of the circuit. Another, more modern part that might be used is the Vishay TCST1103.
Replacing an opto is straightforward, but the boards are often fragile due to being subjected to long hours of excessive heat. Parts should be replaced only when absolutely necessary to avoid additional damage to the PCB.
OEM Clock Boards
Part numbers: A-16219 (hour) and A-16220 (minute).
The Twilight Zone playfield clock toy employs an ingenious method of driving and detecting the minute and hour hand positions. Two boards are sandwiched together, one with four optos to detect the minute hand and one with four optos to detect the motor rotation position and therefore the hour hand.
This board has been problematic over the years as the original incandescent lamps burned very hot, increasing the temperature inside the clock casing enough to damage the circuit board components. Numerous aftermarket clock boards have been offered with varying degrees of success.
Note that the schematic contained in the manual for the clock board lamps shows four diodes (D1-D4). During production, those diodes were swapped with "zero ohm jumpers". The reason for this change was that Williams originally intended the four lamps to be part of the lamp matrix and therefore individually controllable and also therefore requiring an associated lamp matrix isolation diode. When Williams decided to drive these four lamps via general illumination power, those diodes were replaced with "zero ohm jumpers" since diodes would have reduced lamp intensity and the lamps no longer required isolation in a lamp matrix.
Aftermarket Clock Boards
Pinball Lizard - No Longer Available
This was the original replacement clock board. It was a clone of the original design but with cooler LEDs instead of lamps. The board did not resolve the opto issue, so don't be surprised to find one of these showing inconsistent operation.
Rottendog - www.rottendogamusements.com
A clone of the original circuit but laid out onto one board instead of two. Rottendog had a supply of optos that meet the original specs. These boards are still subject to the original opto design problems but are unlikely to fail in home use.
Casper's Electronics
This aftermarket board uses TCST1103 optos and 12V LED strips for general illumination.
Incoming GI power of about 6.3VAC is rectified by two onboard bridge rectifiers and supplied to each of the two general illumination lamp strips. Since 6.3VAC is nominally rectified to (6.3 * 1.414) 8.90VDC, the LEDs are underpowered. Some users have reported dim or not lit LEDs, which is not surprising.
Pinball Haus
DumbAss' Clock Board
As of early 2025, PinSider "DumbAss" has created another very nice aftermarket board, that can be ordered in a variety of PCB colors (white shown here, red also available, and perhaps other colors. The board can also be ordered with soft white, warm white, or color matching LEDs. Installation is a snap and the board works perfectly. The board also uses Vishay TCST1103 optos. The board is unique in that it provides a trim POT to adjust the brightness of the LEDs.
More about "DumbAss'" aftermarket PCBs can be found on PinSide here.
Replacing the Lamps with LEDs
The lamps are easily replaced with LEDs. The biggest challenge is working with possibly fragile (roasted) PCBs.
- On the original clock board, replace "diodes" (really zero ohm jumpers" D1 - D4 with a current limiting resistor of at least 75 ohms. 150 ohms works nicely. #Remove the OEM lamp sockets.
- Install your choice of LEDs into the OEM lamp socket through-holes. Since the LEDs will be driven by AC voltage, polarity doesn't matter. But since the power is AC voltage, the LEDs will be dimmer than if powered via pure DC voltage.
- Bend as necessary to disperse light as desired.
Reassembling the Clock
At left is shown the exploded diagram for the clock mechanism as can be found in the Twilight Zone manual.
Gumball Machine
The Gumball Machine and Geneva Switch: Balls jammed in gumball machine; switch xx error
Mini Playfield
Servicing the Twilight Zone Mini Playfield: "Magna-Flip" not working
- Make sure that the connectors for the mini playfield are connected correctly. Two connectors are identical and can be swapped around. If this happens, you will also likely have to replace the optos at the entrance and exit of the mini playfield since the voltage for the magnets would have blown the opto LEDs.
Clock and Slot Machine Targets
These targets take fast balls from the flippers. These fast balls lead to airballs, damaging the playfield. The targets also get beaten up and broken. It is a good idea to replace them with reinforced targets from Pinball Resource, or you can make your own reinforced targets with parts from Pinball Life. Also, the aftermarket slot machine scoop from Mantis Amusements has a reinforcing bracket. Finally, you can fabricate a rod that holds the slot machine target in place. Even with the reinforced targets, it is a good idea to have some kind of brace (either the Mantis scoop, or the rod) to ensure the target does not bend. The reinforced target tends to transfer more force to the under playfield wood.
Mini playfield wiring
The switch wires, opto wires, and light bulb wires on right side of mini playfield can get a lot of ball hits. Keep an eye on them for wear, breaks and shorts. A break can happen inside the wire casing where you can't see the damage. Heat shrink tubing over them can provide a little armour for them.
Replacing Original "Blinker" sockets with Bayonet Sockets
Twilight Zone originally shipped with wedge style blinker bulbs #545. These bulbs are obsolete and very pricey. Replacing the original wedge style sockets with bayonet sockets allows the use of inexpensive #455 blinker bulbs.
Pull the wires from the IDC connector on the black wedge style sockets. Strip back the insulation where the wires originally pressed into the IDC connector. Staple a bayonet base socket into the location. Solder the original wires to the socket's solder tabs. Insert a #455 blinker and enjoy the cheap light show.
Alternatively, a number of vendors have made #545 LED blinkers available. While they tend to have a slightly "blue" tint, they do make an attractive alternative to modifying your Twilight Zone.
Pop Garden Posts (or not)
Twilight Zone was originally designed by Pat Lawlor without the two posts (with 1 inch rubbers between them) separating the red and orange capped pop bumpers in the pop garden. The story goes that Pat was frustrated with player complaints about quick drains from that area, walked into Williams one morning, drilled two holes in the pop garden area and installed the posts. And so it was from that point on.
If your game has these posts, you can remove them and "plug" the holes as shown in the picture at left.
Misc
Coil Sleeves
03-7066-5 flippers x4
03-7066 Total=10 outhole kicker x1 slingshots x2 bridge diverter x1 right diverter x1 rear diverter x1 a-16647 assembly x1 jet bumpers x3
03-7067-5 Total=3 ball popper x1 eject assembly x1 knocker x1
03-7067 kicker assembly x1
Return to Williams WPC main page.