The pictures below show the End-Of-Stroke (EOS) switch contacts for the flipper assembly.  Notice on the top picture that the contacts are open indicating that the flipper is energized (the flipper button is depressed).  The second picture shows the same contacts when the flipper is de-energized (the flipper button is not pressed). 

I've also included a couple of pictures of EOS gaps on a Twilight Zone (gasp - this is supposed to be an EM page) to illustrate the EOS gap. There's also a picture of a flipper opto board that was used in some newer games that actuates the flipper assembly. 

What's important to know about the EOS switch?

Let's say that you have the type of game that has 3 lugs on the flipper coil and that it uses an EOS switch that is normally closed when the flipper button has not been pressed. There are two windings for a coil of this type with one of the windings being the "power" winding, and the other winding is the "hold" winding. When the flipper is at rest, as in this example, the EOS switch is closed. This means that the "hold" winding is bypassed by the EOS switch. Then when the flipper button is pressed, the "power" winding causes the plunger to pull in which causes the flipper to rotate upwards. Just before the flipper rotates to its upper most position, the flipper "pawl" strikes the EOS switch and causes it to open. When it opens, the "hold" winding is now in series with the "power" winding and because it adds to the resistance of the "power" winding, less current travels through both of the windings. With less current going through the windings, the flipper button can be held in and the flipper will remain in its uppermost position for a long time without burning the flipper coil due to excessive heat.

If your flipper(s) appear to be lazy or weak, there's a good chance that your EOS switch isn't cleaned or is pitted, or is misadjusted so that it isn't completely closed when at rest. The other possibility is that the EOS switch opens prematurely when the flipper rotates upward. This means that the "power" winding wasn't in play long enough to give the flipper the "oomph" to send the ball all the way to the top of the playfield.

The "hold" winding's role is to allow the flipper to be held in the upward position (trapping a ball for example) for long periods of time that the "power" winding can't accomplish without burning up. If you find yourself playing a game and you've been using the flippers a lot, or you've been trapping a ball and you begin to smell something electrical burning, TURN OFF THE GAME! You need to look closely at the EOS switch and ensure it is opening about 1/8th of an inch before the flipper is in its uppermost position. The smell of something burning is your flipper coil that's beginning to fry because the "hold" winding isn't in the circuit and all of the current is being drawn only through the "power" winding. The "power" winding is only intended to be used for the duration it takes to send the flipper upwards and then the EOS switch adds the "hold" winding to the circuit which reduces the current drawn and won't cause the flipper coil to fry.

Newer games (newer than EMs and some solid state games) use a flipper driver transistor that can go bad or even fry if excessive current is drawn. Just because your game may have a flipper fuse doesn't mean that parts can't fry. I've seen many games that had a fried flipper coil never blow the flipper/game fuse. The coil sleeve melted as the wiring insulation in the flipper coil began to fry and still didn't blow the fuse. Usually the owner will smell something burning or they saw smoke suddenly start showing up as the flipper coil began to fry.

So the important lesson here is that your EOS switch needs to be properly clean and adjusted to achieve proper flipper action, and if you smell something electrical burning, TURN OFF THE GAME before it damages more parts.

(click picture to enlarge)


End Of Stroke Open
Flipper Button Pressed


End Of Stroke Closed
Flipper Button Not Pressed


TZ EOS Open Switch
TZ EOS In The Open Position
(Flipper Button Not Pressed)


TZ EOS Closed Postion
TZ EOS In The Closed Position
(Flipper Button Pressed)


TZ Flipper Opto Board
TZ Flipper Opto Board



All Graphics & Text Steve Corley

The pictures you see were created by Steve Corley unless otherwise noted.
Unauthorized use is strictly prohibited