Here's the skinny on the Dremel and why it's useless for coil voltage switches...

Before i explain the why and how, here's the data points.

Latest example: Gottlieb Mibs.
Problem: It was having a problem resetting the score reels. I could see it trying, the score reels would twitch. But not getting enough pulse strength to make the reels move.

Issue: score motor switch at 1A. This is on the lowest score motor position, and it's a large contact switch. It gets pulsed many times per rotation of the score motor. Switch adjustment was good, narrow gap (as i always do.) But clearly the switch was the issue. How do i know? If i put my big fat finger on the switch contacts, forcing them together with greater pressure, the score reels would easily reset.

This is a clear case of a problem switch. It was adjusted perfectly too, but clearly the contacts are dirty or damaged. So, like i do a lot, break out the dremel with a stainsteel wire brush. Clean the contacts. Re-adjust the contacts (because the wire brush activity always changes their gap.) Restart the game. THE PROBLEM IS WORSE. The twitching is gone, now there's NOTHING.

Fix: break out an automotive gap file and file the contacts. Restart the game. Works perfectly.

Now this isn't just some one-off thing. To prove to myself that the Dremel is only good for selected items (i.e. it's generally just a waste of time), i've been experimenting with this for the last 8 or 9 months. I fix A LOT of Em's, and when i have a problem, my first reach is for the Dremel. And the bottom line is this... on coil contacts, IT'S USELESS. In every single case, it results in no change, or making the problem WORSE.

So why is this? here's where it gets complicated...

when a coil energizes, it's through some switch contact. In the above example, the score motor contact at 1A is pulsing four score reel coils, to get them to "zero". As a (30v or 50v) coil energizes, a magnetic field is created. When the power to the coil is removed, the coil collapses. When this happens, you get an EMF backflow of *twice* the energizing voltage. This is what creates though infamous "blue sparks" inside an EM game.

Note the blue sparks does not happen on light switch contacts. because that's only 6 volts, and it's really not a coil (it's a light bulb), you just don't get that. Also note this is an AC thing. On games that use DC, a coil diode can be implemented. This will stop the back flow and "blue spark" issue. But the number of EM games that use DC voltage is small (though a good deal of Williams/Bally games use DC on pop bumpers, only.)

Now that blue spark thing is important. It's a lot of energy. And the way these games are designed is that if there's a lot of current though the powering switch (either front flow or back flow.) The blue spark is so hot, it can actually deform or pit the switch contact. This is why Gottlieb used Tungsten contacts (instead of silver) on high contact switches. But it still happens, over time (and there's NO em that isn't at least 40 years old!), the coil voltage switch contact deform and wear.

No bring in the Dremel. What does it do? well basically it polishes the contact. But it doesn't fix pitting or deformed contacts. It just can't do it! It's a freaking wire brush!! That's why the dremel is USELESS on this type of switch contact. It may make you feel better, but it's accomplishing nothing beyond that. In fact, it can make things worse. It's easy to make the switch gap adjustment change, and it's also easy to knock off the nylon lifters (as used on score motors.) Basically you're creating more problems than you're solving.

So how do you actually fix the issue. A FILE. frankly i don't care what kind, but a FILE is the only solution. The pits need to be physically removed, and often, the contact re-shaped. A dremel isn't going to do that.

So now now back to light contacts. Why does the dremel work well there??
It's simple really. But let's make it a bit more informational...

In the case of a 6 volt switch, any sort of junk on that controlling switch can easily make a light not work. Look at voltage like water and a funnel. 6 volt switches are a small funnel with a small opening. any junk that falls into the funnel can easily block the output of the funnel. 30 or 50 volt switches on the other hand are larger funnels. It take more "crap" to clog the funnel output. (but when they do get clogged, you need a roto-router to fix it, not a tooth pick!)

The dremel/steel brush arrangement is really good at removing junk. It won't re-shape a contact or remove pitting, but on a light 6 volt switch contact, you don't need that. In fact, you don't want that! that's why the dremel is the ideal tool for this situation. A file can actually make switch contacts that control lights worse, because the contact points can be changed, causing additional problems.

To that point, the dremel does have other good uses. Like on Jones plugs (the male side.) It really does this well (and quick!)

Another thing... be aware that these steel brushes can be contaminated. So if you use the wire brush on say a circuit board, do not use it on an EM game! So buy a lot of brushes is what i'm saying, and don't be afraid to change them often. Otherwise you can bring contaminations from one situation, and spread them onto another game.