A Practical Guide to Fixing Pinball Flippers
by Jonathon Deitch
e-mail litz@bellsouth.net

The following material applies to System 11 and WPC games from Williams, mainly, as that's where my area of expertise is concentrated ... parts of it may or may not apply to flippers from other manufacturers, but remember -- all flippers work alike, no matter the mechanism or driving electronics (if any).

Flipper Systems
Williams, over the years, has used two main types of flippers. The original flipper setup is very simple -- 50 volts is fed to one side of the flipper. The cabinet switch is connected into the ground line on the other side of the coil. Pressing the cabinet switch completes the circuit and up goes the flipper. A relay in the backbox, controlled by the computer, switches the ground on and off, thereby enabling/disabling the flippers. This worked well, but holding the flipper button in for extended amounts of time causes LOTS of heat and many coils melted as a result.

Williams' answer was the parallel wound coil. The parallel wound coil is actually two coils in one. One part is a coil made of light guage wire and many, many turns. This creates a weak magnetic field and therefore little heat. This is used to hold the flipper up after it's reached the up position. The holding side of modern coils can hold a flipper up for indefinite periods of time, limited solely by the ability of the drivers and power supply to keep the current flowing. The other part of the coil is a coil made of heavy guage wire and a very small number of coils.This creates a very large magnetic field and is therefore used for the initlal pull-in of the plunger.

Older systems using the parallel wound coils use an End of Stroke (or EOS) switch as a means of switching off the high power coil once the flipper has made it to the raised position. Failure to do this will quickly result in the high power coil overheating and melting. The EOS switch is used to short out the holding side of the coil, delivering the entire load of current to the high power coil. The EOS switch is therefore normally closed.

When the flipper hits the raised position, the EOS paw on the flipper crank pushes the blade of the EOS switch away, opening the switch. The flipper current is now allowed to flow through the entire coil, first the holding circuit, then the high power circuit. The increased wire is more than enough to weaken the magnetic field to holding levels and prevent meltdown.

A snubbing capacitor is wired across the EOS switch terminals to help prevent current spiking that results in a brilliant light show of electrical sparks.

With The Addams Family in 1992, Williams introduced the Fliptronic system. Fliptronic is identical to the older setup mechanically, but the EOS and cabinet switching is moved to a computer controlled driver board. The cabinet switch and EOS switches became switch inputs to the computer (which is why Fliptronic EOS switches are normally open instead of closed). The holding and power coils are connected separately to computer controlled driver circuits on the Fliptronic board. This allows the computer to read the flipper and EOS switches as standard switch inputs as well as drive any flipper coil independantly of the player. This allows the computer to fire flippers during ball searches, should a ball become stuck behind one, and more importantly, allows Thing to do his thing !

Flipper Plungers / Coil Stops
A flipper works by pulling a metal shaft along a sleeve inside a coil. As you don't want the shaft, called a plunger, exiting the other side of the coil, there's another piece of metal, called a coil stop, there to stop it. After thousands of flipper presses, these two pieces of metal eventually get flattened and the tips begin to spread out. This is called mushrooming. It causes friction against the coil sleeve resulting in a weak flipper.

Eventually, the mushroomed end of the plunger will wear right through the sleeve and start tearing the inside of the coil apart, resulting in a shorted coil and usually then a complete meltdown of the coil's interior.

That's the basic mechanics involved in a flipper -- the plunger gets pulled into the coil, and it drags the flipper shaft around in a circle, rotating the paddle as a result.

Common Flipper Troubles, Symptoms, and Solutions Symptom :

No flip. At all.

* Check the fuse. If it's good, make sure your main 50vdc power is getting to the flipper (check the manual for the proper wires to check). If it is, make sure your flipper cabinet buttons are okay. High voltage switches (non-Fliptronic games) are notorious for oxidation buildup on the switch contacts. Drag a business card through the contacts to clean them. The 50vdc side of the coil, BTW, is always the end terminal where the banded end of the diodes are. * Fliptronic systems on WPC games have coil tests specifically for flippers. This helps you identify what coil is the problem. The Fliptronic system also continually tests the EOS switches and cabinet switches. Problems will be noted on the game's error report upon entering test mode.

* Still no go ? Remove the coil, unsolder its diodes and check for continuity. An open circuit, after the diodes are removed, for either part of the coil (test the common terminal to each of the other terminals one at a time) indicates a bad coil that needs replacement. Usually the holding side of the coil goes bad, but the power side has also been known to fail, especially on non-fliptronic systems with faulty EOS switches.

* Still no go ? Follow the circuit from the transformer right on through the power supply until you find the point where it stops. That'll be the problem.

Symptom : Weak flip.

* Check the plunger shaft and coil stop for mushrooming. A mushroomed plunger dragging against the coil sleeve is a classic cause of a weak flipper. The plunger should slide smoothly and cleanly back and forth inside the coil. Any resistance indicates a problem.

* Also, check for a worn out EOS switch, if this is a non-Fliptronic system. An EOS switch with high resistance will never cause the holding side of the coil to disengage from the circuit. This puts the coil permanently into a "holding" state, and it can't provide power, not near enough, for a strong flip. Symptom : Flipper Bounce (esp. on newer or new games)

* This is what has been reported on rec.games.pinball as "new flipper" syndrome -- where a brand new game has bad flippers ... usually flippers that stay up a bit after the button is released. This is (IMHO) due to the plastic interuptors used on the flipper button optos. The plastic heats up and its elasticity is serverely affected, causing it to not instantly spring back when the button is released. the only solution is to replace the plastic (and hope) or put in a metal interuptor, like TAF and TZ use. A temporary solution is to use rubber bands stretched across the back of the plastic interuptor for auxillary tension.

Symptom : Flipper Chatter

* Broken holding (low power) side of a coil or bad low power driver on a Fliptronic board. Possibly also a broken wire to the terminal for the holding side of the coil. Non Fliptronic games will chatter like a machine gun, Fliptronic games will flip twice, then give up.

Symptom : Stuck flipper

* EOS paw on crank has a worn out rubber sleeve. This can etch a hole in the EOS switch into which the paw then gets stuck. Put new 1/4" heat shrink tubing on the paw and replace the EOS.

* Flipper crank tightened too tight on shaft. This causes excessive binding between the playfield bushing and the crank assembly. There should be around 1/32" (enough for a slight wiggle) of a gap. If the paddle does not have a slight bit of vertical movement, it's too tight. Most games are shipped with an adjustment tool you can use to check for proper spacing.

* A mushroomed plunger or driver failure has caused the coil to meltdown around the plunger, causing it to stick in the up posistion. If you smell a strong burning plastic odor, this is likely the cause ... If this is a Fliptronic game, fix the driver (if it's blown) FIRST or you'll end up burning another coil out ! Notes on shopping flippers ...

Whenever a new game comes into my store, I always replace just about everything. This is because I've found most other places don't ever check flippers and end up turning 'em into junk over time. Worn out flippers are essentially unfixable. I replace : Coil stops, Coils (if worn out), Coil Sleeves, Cranks, Crank Links, Plungers, EOS switches, Paw rubber, and the Return spring. Coils don't need replacing if a new sleeve can easily be slid in. Otherwise the coil has expanded from heat of operation and will likely cause a new plunger to bind.

Fliptronic boards use a standard driver chain similar to the WPC power driver high power solenoid drivers. These *can* blow, so make sure they're okay. It's *very* rare for the TIP36C drivers to die, but fairly common for the TIP102 drivers on the holding circuits to fail. If you have a known good coil and a Fliptronic game with chatter, it's likely the TIP102 for the low power driver. Opto driven flipper switches are run by LM339 voltage comparators.

If either of the optos or the comparator aren't working properly, you can have a weak flip, bad EOS hit, both or none. If everything else has been replaced, this is likely the fault. Switch the opto boards (the left and right ones are interchangeable) and see if the problem follows the board. If not, replace the LM339 that drives that opto.

Note that the opto board power is jumped through the left opto board -- both must be plugged in for the right one to work ... NEVER EVER EVER oil, grease, lubricate or do ANYTHING to a flipper plunger or coil. Same for standard soleniods. The action of the plunger rubbing against the nylon sleeve creates a natural graphite coating that acts as a lubricant.

External lubricants attract dust, metal shavings, pieces of solder or wire or whatnot. These get down inside the flipper coil and cause all kinds of hell. Don't do it, or you'll be replacing the plunger, coil sleeve and maybe the coil too.

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