One of my arcade cabinets, a Super Neo 29 Candy, came with the original mid-90s era buttons. They were in rough shape, so I removed them immediately and put new ones in. But the original buttons were very interesting: they were magnetic.
SNK opted for Omron's XW6Z-0011 series buttons, and while they fit where any normal 30mm arcade button would, they are built differently, and they operate with magnets and vacuum-sealed glass tubes.
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When installed in a control panel they use these flimsy-looking wings to stay in place. They're more effective than they look.
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Here's the disassembled pieces. From the right, they are the main shell, the magnetic plunger, return spring, button, and switch assembly. Unlike most arcade buttons the switch assembly does not separate from the top bucket as a swappable component. The bucket and switch housing are one piece, and the switch assembly needs to be pried out with a screwdriver. So, while you might swap Sanwa or Seimitsu switches between buttons, you can't put these Omron reed switches on any other button without significantly re-designing the whole button.
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A close up shot of the plunger, with the magnet installed.
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This is the switch itself. The reed switch is soldered at the top and bottom to the two terminals at the base of the switch.
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And here's a very close view of the reed switch itself. The top and bottom are separated by a fraction of a millimetre, and the bottom is pulled up with a barely audible click when the magnet is close.
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And here it is in motion. You can see the bottom reed connect with the top one as the magnet passes.
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