Twilight Zone Pinball Machine


    Stripping and cleaning this machine was no more work than the previous WPC machines that I have refurbished.  My tip to you is to pay attention to the dissassembly sequence of the top right portion of the playfield.  Make a note of the order of the components removed, so that they can be reassembled in the reverse order.  The layering of the parts will require this method of reassembly.

    stripped playfield

    Playfield stripped of all parts.  Most of the parts under the playfield
    were also removed and cleaned or replaced as needed.

    Completely reassembled playfield.  I made protectors for all of the
    plastic that can be hit by a fast ball.

    I bought this authentic gumball machine at a local thrift store for $18. 
    It is made of glass and metal, and looks very similar to the one on the translite.


    Repainting the cab

    Although the head had no fading, the cab did.  Since I do not have the equipment, experience, nor the space to properly redecal the cabinet of the machine I decided to repaint it with opaque and translucent paints.


    Before and after pictures of the cab.

    The result turned out very well.  Two aspects that interestingly do not show up in the above picture is that the red area of the sunset is gradual from dark red to orange.  This was done with blending using two colors of paints.  The second aspect is that when viewed close-up, you can see some streaking in the dark paint due to brush strokes.  This kind of restoration technique is not for the purists, but I would rather have well adhering factory decals than risk having wrinkly ones.


    Pop Bumper Light

    One of the difficult part of rebuilding the pop bumper is how to handle the leads of the light inside the pop bumper.  They are originally stapled down to the underside and then soldered to their connections.  Refurbishing them means finding a means to get a staple gun and soldering iron deep into a forest of wires and mechanism bodies.  Examples of how difficult this can be are discussed here.

    I came up with an alternate method that simultaneously fastens the lead to the underside, and connects to them electrically.  The method is very simple, and is illustrated in the photo below.


    Detail of how the popbumper light is attached.

    The connection is simply crimped or soldered onto a lug, and then the lug is screwed down with a self-tapping screw and washer.  Then, the lead of the pop bumper is slide under the washer, and the screw is tightened with a long socket driver.

    Clock Lighting

    A common problem is that the clock overheats due to the four #86 bulbs in it.  These consume about

    200mA each. I changed them to #84 bulbs, which consume only  40mA.


    A normal #86 bulb is in the bottom left,
    while a lower power #84 is in the top left.

    The result is that the clock is not as bright, but it is quite bright enough.  At some point in the future, I will also try LEDs.

    Third Magnet

    A common mod is to add a third ball-holding magnet to the playfield.  The first work to be done is to drill the ball guides to accept an optical sensor.


    Ball guides drilled for the third magnet.  The optical beam is right

    over the third inner spiral band.  Compare to this page.

    Once the ball guides were drilled, the next step was to add the opto sensors.  I received a partial kit as a generous gift from Martin, and had to modify them slightly because the height of the ball guide holes were not quite right.


    The opto sensors installed.  The receiver is at the top, the emitter at the bottom.

    In Martin's instructions, he recommends putting the two emitter LEDs in series by using a harness.  I decided to simply solder them together as shown above.  The new opto switch appears as #82, which is called "Unused" in the DMD display during switch test.

    Next was the most difficult part: drilling the playfield for the magnet pole.  First, some numbers: The width between the metal ball guides is just under 1 5/8".  The diameter of the ball is 1 1/16". This means that at most the ball needs to be moved laterally (to center it over the magnet) about 1/4".  So if the pole were only 1/2" wide, it should still allow the ball to touch its edges even if it were hugging a ball guide.

    One small problem to solve was the magnet pole and bracket. These are $40 as a set, and my initial impression was that they were not available.  After a conversation with Martin, I hit upon the idea of simply using a bolt threaded into the playfield.  This would perhaps allow the use of a smaller bolt than the 3/4" size of the conventional magnet pole. If successful, it means I would be able to put a smaller hole in the playfield.  

    I set up a small test jig to find out what size bolt was the smallest I could use.  This jig is shown below, and shows the two ball metal ball guides, various holes for bolts that I tested, and an opto that is wired to appear on the switch matrix as the left spiral opto.  Not shown is the magnet under the plywood plank being held by the bolt under test.


    Bolt size test jig.  In 'Magnet Test', the ball is grabbed when the opto beam is broken.

    In the test menu, I set  up for 'Magnet Test'.  I could then fire the ball down the guides, and see if it grabs the ball properly when the opto beam is interrupted.

    My first test was to use a 1/2" bolt that did not break the top surface of the wood.  I was hoping that it would be possible to leave about 1/10" of the surface wood and playfield paint so that the new magnet would be invisible.  This addresses everyone's fear of drilling straight through the playfield.  Tests showed that this idea, although appropriate for the mini-playfield, is not effective enough to catch a fast ball.

    I then tried various sizes of bolts, and found that at a minimum, a 3/8" bolt was needed to catch the ball.  That is the bolt that is embedded in the test jig in the photo above (the duct tape is covering other test holes).  For operational margin, I decided to use a 1/2" bolt in the playfield.  Specifically, it is a 1/2" x 1 1/2" hex head bolt. 


    Drilling the playfield.  Unfortunately, the hole is out of focus, but the edges of
    the hole are very clean.  None of the tear outs I was fearing.

    I used a brand new 7/16" spade bit with very sharp tines on the outside edges to drill the playfield.  One complication was that I had mylared the entire top of the playfield, and I did not want to have tears along the hole edge.  This is why I felt a sharp spade bit was the right solution.  Indeed, by going very slowly with the first touch of the outer tines, I was able to make a very clean and sharp hole.  Unfortunately, due to the depth of the above image, the foreground is in focus, and the subject drill hole is somewhat out of focus.

    I then used my 'Dremel' tool with a miniature drum sanding bit to gently open the hole up towards 1/2".  I tapered the hole a bit so that the top (near the playfield paint) is slightly smaller.  I had previously ground down the 1/2" bolt completely flat, with a slight bevel.  This allowed the slight taper at the end of the hole, so the hole at the playfield surface is 7/16".

    The magnet was mounted with the bolt, and I had to tighten down the last few turns with a ratchet.  This ensures the right balance between secure mounting and no splitting of the playfield wood.  Note the large fender washer at the bottom of the magnet.  If I recall my E-M fields class, its use causes the magnetic field lines to pass inside the steel fender washer to conduct around the end pole, and 'focuses' the field lines to the top, towards the ball.

    The bolt was tightened until its ground-down end was flush with the playfield.


    New magnet mounted with the bolt (left).  This latter element thus serves double duty as the magnet pole and the mounting bolt.

    Finished installation.  Note the painted black ring around the pole.
    This is meant to match the artwork on the existing poles.


    One thing I have noticed with the third magnet installation of others is the missing black ring around the new magnet.  I decided to use some acrylic to touch up that area and add that ring.  Note that the entire top half of the playfield is mylared, so I was simply adding paint on top of the mylar.  I then covered the spiral with another small patch to protect the touch up.

    Lastly, I used a spare ROM to program version 9.4H of the game code into the CPU board.  This fully utilizes the added hardware.

    Thanks to Martin for his opto parts.  I only had to purchase the
    magnet and some bolts for $30 total.

    Apron cards


    I printed a set made by Vinito.  They look like they really belong there.

    'Lost' Spiral Plastic

    There is a yellow colored light at the left entrance of the Spiral loop that appears to have no function.  It turns out that there was a plastic at that location that was removed from the production version.  This can be seen here.


    Note the yellow light at the left entrance of the Spiral Loop. 
    It does not appear to have a purpose.

    The set of three plastics that John Estill sent me (at no charge I might add) included this lost plastic.  I made a small bracket to mount it near the loop entrance.


    I made a bracket and mounted the plastic above the entrance.  The yellow lamp is mounted to the top right hole and lights up the words when it is on.

    Blinking lights in the backbox

    There are supposed to be two types of bulbs in the backbox (behind the translite).  One is a regular #555 wedge style bulb, and the other a blinking #545 (using a bimetalic switch).  These latter type are mounted in a black bulb holder instead of the white.  However, bulbs of these kind are almost impossible to find and can be very expensive.  I decided to change these holders to a bayonet style so that I could use #455 bulbs.


    The back of the original lamp socket for the blinking #555 bulb.

    The light panel is only 1/2" thick, so low profile bayonet bulb holders are needed for this mod.  I decided to fasten them with a single self-tapping screw instead of a staple.  I bought these sockets at the Allentown '08 show, so I do not have a part number.


    New lamp socket for the self-blinking #455 bulb.

    The two bulbs side-by-side.  Left:non-blinking, right:blinking.


    After the translite was reinstalled I realized that the location of the six blinkers is not totally random, but the following elements are highlighted by a blinking light:

    Faceless mannequin

    Gumball machine


    Small Invader Robot

    Slot machine

    Dummy in case

    The end effect is so good, I may add it to my other machines. 
    Total time was about 30 minutes.

    Dressing up the gumball machine

    A very common mod is to light up the gumball machine. I received the kit as a gift from Martin.  It includes a small circuit board that goes into the top of the gumball dispenser.  The excellent installation instructions are here.


    The lit gumball machine after installation.  It is normally lit by white LEDs, and flashes red when it is ready to be loaded by the player.

    In addition to the lighting, I put in a small quantity of glass irridescent beads to represent gumballs.  This was the biggest hassle of the installation because I had to remove the dispenser and open the clear dome halves.  I was not able to squeeze them in from the top.

    Although it looks very bright in the above image, from the player's perspective it is a nice balance of brightness that dresses up a dark corner of the playfield. 

    Reassembling the TZ clock gears

    After reassembling the clock a few times, I realized that the alignment of the big black hour hand gear to the rest of the clock is important.  If that is not aligned properly, the clock will not show perfect "noon" after the power-up homing operation.  In addition to the cosmetic aspect, this misalignment may affect the sequencing of the optos as the clock moves, which may confuse the CPU.  A reader on RGP (BP) suspected that was his problem, so he asked me to figure out how the gears should be aligned.

    This is how to register the big black gear:

    On the front face, there is a tiny hole in the drive shaft of the minute hand (under the hand).  With all the white gears in place, and the big black gear out, rotate the minute hand shaft until that tiny hole points to 12 o'clock.   See the second picture below.

    Look at the back of the big black hour hand gear.  Locate the line that is on the back of the disk and that is highlighted with a red arrow in the image below.

    Locate the drive gear of the hour hand.  This is near 7 o'clock position.  It is the gear that actually engages with the black hour gear.

    Slide the hour hand gear over the minute hand shaft, and engage the teeth of the gears such that the line is over the drive shaft of the drive gear as shown below.  The view in this photo is from the 9 o'clock position.

    Before reassembling everything, place the hour and minute hand onto their shafts to check alignment. 

    If it looks good, remove the hands, and reassemble the clock.


    Note the location of the index mark (red arrow) with respect to the
    hour hand drive gear. This is viewed from the 9 o'clock position.

    Start with the hole in the minute hand gear pointing to noon.  The shadow
    of the hole can be seen on the white background. 
    This viewed from the 12 o'clock position.


    I also took this opportunity to very lightly lube the white gears in the clock with plastic compatible Teflon lube.  I put a small dab on each engagment point between two gears.  Initially, it did not seem to make a difference, but I could tell half way my first game that it was quieting down.  The clock now runs so smooth, I think this is a very important mod to make.  Thanks to Ben Patrick for sending me a small amount of this lube.

    Auto Ball Launcher mis-fire

    A common problem with this machine is the operation of the auto ball launcher.  On my machine, the problem is that about one third the time, the ball (once launched) will rattle near the ball gate area, and lose all its velocity.  It then makes it onto the playfield, but dribbles out of the right end of the spiral loop.

    I had done some fixes in the past, and then posted for help on RGP.  This gave me some ideas to take another look.  After some tests, I found the main reason the ball was hanging up on my machine.


    When the ball launch fails, the ball bangs into the area in the blue
    circle.  I had previously removed the rubber ring from the post.

    By putting my hand on the ball guide circled above, I could tell that failed ball launches was associated with the ball banging into that area.  I had previously removed the small rubber ring on that post, and that improved things a bit.  In my opinion, the angled ball gate below this post tends to deflect the ball to the right, and into the post.  When I opened the ball gate manually, things improved dramatically.  I needed to find a way to get the ball to run up the ball lane on the left side, so that some deflection would not cause the ball to bang into the post.  This is consistent with my results in the past as leaning the machine slightly to the left produced better launches.

    Another issue suggested by responders to my post on RGP was to make sure the ball launch bracket is not sloppy.  I found that the major source of looseness was the connection from the angle bracket to the plunger.

    The solution for both of these was to add washers on the left hand side of the bracket.  This causes the launch bracket to hug the plunger linkage, and to turn to the left slightly, and greatly reduces the slop of the mechanism.


    Mod to reduce slop in the kicker, and to rotate
    the launcher slightly to the left.  This consists of
    two washers shown with the arrow.

    After this mod, I was able to have a successful test of 30 consecutive successful ball launches.

    (c) 2009 Edward Cheung, all rights reserved.