the essential PSU guide

my pictorial guide to how to adjust your power supply.

if you have a game that resets or freezes up or even completely blacks out, chances are you need to check your voltage. I’m aware there’s power supplies that have indicator lights telling you the voltage is too low or high, but I don’t trust that feature, especially from inferior-made units. this will show you everything you need to know, and explain a little bit of science behind it.

before I get into the thick of things, I will point out that game logic operates within a voltage tolerance of 4.75-5.25V. voltage below the tolerance will yield components that probably won’t operate due to not enough power. voltage above the tolerance can run the risk of PERMANENTLY damaging components. this guide serves as a means to show you how to accurately test and safely adjust your voltage to preserve your hardware. I personally adjust voltages to 5.10V at logic, and sometimes 5.05V on more sophisticated and newer Japanese hardware (that’s VERY voltage sensitive, and you will read about later).
first of all, you will commonly encounter one of these types of power supplies.

screw terminal type


box type (with molex plug, typically in 9-pin variety, but sometimes with 12-pin)


the wiring that connects to the power supplies does not adhere to any one standard across every make of video game. the most common arrangement I’ve seen is +5V: red, +12V: orange, -5V: yellow, ground: black. variations I’ve seen are +12V: yellow and -5V: white. (on box type power supplies). you will of course have to verify the colors in a wiring diagram for whichever game you’re working with to be absolutely sure though.

despite being different types, the power supplies pictured above perform the same functions. all video game logic will operate off +5V, audio amplifiers will use +12V, and some games will require -5V for audio. all these power supplies will have an adjustment knob for +5V. this knob exists because each game cabinet is wired differently and your power needs will vary from game to game. here’s a demonstration of the different levels of voltage loss, gradually diminishing from the power supply to the game logic.

speaking of logic, you can typically get away with measuring this voltage at roms, but there’s certain Japanese makes and later model games that used higher capacity roms that will not follow the same pinout shown below. (make note of the U-shaped notch, especially when removing socketed chips and reinserting them — inserting backwards will damage the chip!)


your best bet is to measure the voltage at one of the smaller input chips instead, these usually start with the part # 74xxx. even on the strange Sega hardware I’ve seen these chips exist.

at the power supply (at the +5V and ground or COM[mon] lugs)

at the JAMMA edge

at the logic (or in this case, the sound rom on an NFL Blitz ’99)


you can measure the voltage on the box type units at the red (+5V) and black (ground) wires in the 9-pin molex plug

due to this power loss, the most accurate way to test your voltage is at the logic. it’s good practice to meter at the power supply too, because this way you can see how much the voltage drops. if you notice a substantial drop in voltage between the power supply and logic, one thing you can try is cleaning the edge connector. the tool you use for this task may not be very far away..

a household pencil eraser. the quality matters, as cheaper erasers can leave a residue behind.
I personally go up and down on each individual contact, and then go side to side across the entire edge connector. you’ll probably observe that the dark or foggy finish on the contacts will now look much shinier. an optional approach is to wipe the contacts with 91% isopropyl alcohol, or I have used a fiberglass brush in the past as well (and it worked out nice). re-test your voltages again. did the voltage drop decrease? you’ll probably find if things went to plan that your operating voltage at the logic is a lot closer to what the power supply is pushing out.

really dirty edge connector (notice the oxidation)



JAMMA edge after I cleaned it up

most people resort to turning the power supply voltage up, skipping the cleaning step. while this may work in the short term, please note that on certain games you can damage the edge connector. the dark or foggy finish on dirty edge connectors actually prevents the flow of power, creating resistance, which in turn produces heat. over time the problem will exponentially worsen until it finally burns up the contacts. in the picture below is a San Francisco Rush 2049 board where you can see a repair was made to the edge connector because it burned up previously.


Rush 2049 runs off the Atari Denver hardware, which is a variation of the Midway & Atari Vegas, but with a different video card. handy tip for measuring voltage on these and other games with hard drive plugs on the main board, you can actually measure your +5V logic at the red and black wires on the hard drive power plugged into the board. I have confirmed this is identical on the Vegas hardware compared to any other chips I’ve tested at. cool and handy feature.

newer Midway games with high capacity roms (such as, but not limited to Cruis’n Exotica and Mortal Kombat 4) and I suppose any other game with a security chip can be tested at said security chip. (don’t do this stunt at home, I did this so I could take the picture!)


so as for those sophisticated and newer Japanese makes, I will talk about Sega’s hardware. while this can pertain to NAOMI, NAOMI 2, Chihiro, Triforce, Sammy Atomiswave (which is a variation of the NAOMI), I will speak of it as NAOMI in the instructions.

first of all, Sega uses an entirely different color scheme on their wiring. +5V: yellow, +12V: red, +3.3V: brown, ground: white. there are other games produced by Namco that use Sega hardware that will use more conventional wiring colors like those mentioned at the beginning of this guide.

the Sega NAOMI is a very voltage-sensitive piece of hardware. it’s generally frowned upon to operate them above 5.10V, and the +3.3V line should be adjusted to 3.30V exact. these you won’t have to open up and test at the chips however, you can simply get away with metering at the plugs on the back of the boards (applies to all hardware types listed in this section). I’ve seen sharp voltage drops in Namco games like Maximum Tune and Mario Kart GP, so be certain you don’t measure at the power supply and do it at the board, otherwise if the +3.3V line is set too low the game will not boot.

probably worth mentioning, my Marvel vs. Capcom 2 with the Capcom I/O using a regular non-3.3V switcher actually automatically adjusted the output voltage to 5.00V, so you can probably safely get away with running these anywhere between 4.95-5.10V.

measure +5V at the yellow (+5V) and white (ground) wires on Sega hardware. (Namco cabinets will use red for +5V and black for ground)



measure +3.3V at the brown (+3.3V) and white (ground) wires on Sega hardware. (I think it’s yellow on Namco cabinets)


I will probably make more additions to this at a later date. I hope this helps a lot of people out.