House breaker trips when you switch on a pinball machine

Many owners of System11 games (which include popular titles such as Pin-Bot, Taxi, F-14 Tomcat, Whirlwind, and many more) mave have experienced a problem - when you switch your pinball machine on, the main breaker of your house sometimes trips.
Especially when the electricity in your house has recently been installed and you have fast automatic breakers.

From what I hear this problem happens more in Europe than in the USA. I have no idea if this is because of the 110/220V difference, or because of the type of breaker/electrical wiring used.

This problem is caused because when you switch on the game, the transformer (and other parts of the game) suddenly require a lot of electricity. It causes a sudden load, the main breaker of your house thinks there's a short somewhere in the circuit and resets. Bam - your whole house is without electricity..
There's also a reason why it doesn't happen all the time. AC is a wave which goes up and down, 50 (or 60, depending on what part of the world you're in) times a second. When you switch the game on while the wave is at the bottom, you usually have enough margin so the breaker doesn't act, switch on the pinball machine while the wave is at the top and the circuit gets overloaded.

There are two solutions for this. The first is a workaround - you can add more resistance to the wiring (so the main breaker becomes slower to react), try to plug in your pinball machine in a long extension cord instead of directly into the wall. The extension cord can help solve your problem.

The correct way to solve the problem is to install an NTC. NTC stands for Negative Temperature Coefficient, another word for it is thermistor. It's a resistor that changes its value with its temperature. It's job is to limit the inrush of current when you turn on the machine.
Turn on the pinball machine and the thermistor will limit the inrush of current because of its resistance. Once the machine is on, the resistance of the NTC lowers, not influencing the circuit anymore.

Two NTC thermistors.

Williams noticed this problem and has added an NTC to WPC pinball machines. The older System11 pinball machines do not have this, but you can add it yourself.

Installing an NTC to a pinball machine to pretect the your main house fuse

You can buy this type of NTC at electronic parts stores. I suggest Great Plains Electronics for specialised pinball parts, but many other pinball parts stores also have this part.

Warning ! This part is added to the mains circuit of your pinball machine. Only do this when you are experienced working with electricity and soldering. As this part of the circuit is BEFORE the on/off switch of the machine, be sure to UNPLUG the machine before attempting any of this, because live voltage is present !

The part of the pinball machine we have to add an NTC to is a metal box, located at the bottom right inside the pinball machine.
Unplug the pinball machine, open the cabinet, lift the playfield. At the bottom right (either screwed into the side panel or bottom pannel of the cabinet) is a metal box, with a main fuse and sometimes a service outlet. Unscrew this so you can look at the inside of it.

NTC installation.

In the picture above you see this metal box from a System11 type of game (on the left) and a more recent WPC type of game (right). Although the position of parts has moved a bit, both basically have the same internal parts. Note that none of them has a service plug installed (there's a black square plastic plug in place), if your game does have one, you'll have additional wires going towards it. But for the installation of the NTC you can ignore the service plug part.

I'll first explain what the parts inside this box are. Left box first - the System11 box.
Electricity from the wall comes in at the bottom. In the center there's a large metal box, this is a RFI filter. Because of it, no other electrical appliences get interference from the pinball machine.
The green disk soldered on its lugs (above it in the picture) is a MOV. That is a Metal Oxide Varistor. It's job is to protect the game from powerspikes, like when lightning hits. (when lightning hits, usually you only have to replace this part and the main fuse). European games need a 275 volt MOV, USA games 130 or 150 volt.
There are wires going to the on/off switch (which is in the center top panel, in the picture hidden behind the MOV).
On the top right finally is a main fuse of the pinball machine.

The metal box on the right from a WPC pinball machine is very similar.
RFI filter in the center, MOV attached to it, on/off switch is on the top right, and main fuse is at the top left.

You probably noticed the difference between the two now - with the System11 box there are wires going towards the main fuse, while on the WPC box there is another component (the NTC) installed between the RFI and main fuse.

So to prevent the main breaker from your house from tripping when you switch on the pinball machine, all you have to do is replace the wire between the RFI filter and main fuse holder, with an NTC.

Be careful, unplug the machine, make sure you solder everything well, install heat shrink tubing over the exposed metal parts, ..