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This was the first attempt. A very simple PSU based on 3A (I think?) capable 78xx chips. The only other components are a couple caps to smooth the supply in and out of the regulators. The 12v regulator is wired up to the 19v ac transformer and the 5v is wired up to the output of the 12v regulator. This works fine for small loads, but the neogeo was a bit heavy for it and the regulators heated the make-shift sink up pretty quick and then I think thermal protection kicked in and they started turning themselves on and off which upset the neogeo somewhat. Without cooling (I did try sticking a fan over the psu in the MV1B's case but it wasn't enough) it's a no go.
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After google'ing for a way to make the 78xx's run cooler I discovered a site about the LM2576 switching regulators and ordered the parts need to build +5v and +12v supplies. The 12v LM2576 doesn't work by the look of things, I built the +12v transformer first and it didn't do a shit. I checked everything and couldn't find anywhere that my implementation was different from that in the datasheet/on the DC-DC power supplies page listed below. I built the +5v transformer and it worked first time, so I reckon the 12v LM2576 is dead. I wanted to test the +5v supply on the neogeo to see if it would work but needed a +12v supply to go with it. So I desoldered the 7812 off of the first attempt and rigged it up to a little board and attached that to the +5v switching transformer. Amazingly it works and the 7812 regulator is stone cold! So there can't be all that much load on the +12v.. The +12v switching transformer I built used a massive (size-wise) high amp inductor coil as I thought there would be a lot of load, but it appears you could get away with a pretty low amp inductor or just a 7812 which is easier to implement and takes up a lot less space.