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I have some arcade cabinets with computers in them, and I'm using a regular PC PSU for them, which sucks because it takes up so much space.

I know there are pico-psus on the market, but I don't really get why I can't just take 12v and 5v from the JAMMA harness and wire that in to an ATX connector.

Is it possible to do?

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  • \$\begingroup\$ How much current can your "JAMMA" supply provide? How much current does your motherboard require? Does your JAMMA supply also have the required 3.3V rail? Or the -12V (and sometimes -5V) rails? These are all part of the ATX standard pinout, you know. \$\endgroup\$ – Connor Wolf Apr 2 '14 at 8:46
  • \$\begingroup\$ It doesn't have +3.3 or -12, but I think the motherboard should still power on without these, shouldn't it? \$\endgroup\$ – Cameron Ball Apr 3 '14 at 1:02
  • \$\begingroup\$ I don't really understand why you think you can leave some of the rails out, and it'll still work. Adding more power rails isn't free. It isn't done without a reason. Why do you think they're unneeded? \$\endgroup\$ – Connor Wolf Apr 3 '14 at 1:07
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You can, provided you know the amount of current your motherboard requires, and that the power supply in your arcade cabinet can supply that amount of current.

Furthermore, there is more going on there then I think you think. The ATX standard has 3.3V, 5V, 12V, -12V and sometimes -5V connections:

enter image description here

You would also need to fake the PWR_ON/PWR_OK signals, which shouldn't be too hard (just a resistor pulling the relevant IO lines into the relevant states), though managing power-up and power-down sequencing could be somewhat involved (ideally, you'd want to switch the JAMMA power supply using the signal from the PS_ON line, but that would also require having a working 5V standby source.

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    \$\begingroup\$ Also, the ATX standard specifies that that on power on or off, +12V is always higher than +5V which is always higher than +3.3V. In other words, you cannot turn on the +5V and then turn on the +12V. The JAMMA supply may already follow this, but it's something else to check. \$\endgroup\$ – DoxyLover Apr 2 '14 at 16:09
  • \$\begingroup\$ I know about +3.3 and -12 on ATX. But are those needed to make the motherboard turn on? I don't need +3.3 or -12, so I don't care if they are left unconnected. \$\endgroup\$ – Cameron Ball Apr 3 '14 at 1:03
  • \$\begingroup\$ @CameronBall - How do you know you don't need them? If they bothered to go through the expense of having to add additional wires for those voltages, it's probably a safe assumption that the motherboard requires them to run. It's probably a safe assumption to believe that you need all the voltages on the connector for normal motherboard operation. \$\endgroup\$ – Connor Wolf Apr 3 '14 at 1:05
  • \$\begingroup\$ My understanding is that older CPUs ran on 3.3v and -12 was used for RS-232, -5 for some older floppy drives. \$\endgroup\$ – Cameron Ball Apr 3 '14 at 1:15
  • \$\begingroup\$ I'd suspect that the audio system could very well use the -12V, and most CPUs have been <2V for quite a while. There are local DC-DC converters on the motherboard for quite a long time. I don't know off-hand which rail the CPU runs off. \$\endgroup\$ – Connor Wolf Apr 3 '14 at 1:34

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