View Full Version : Power Supply FAQ

21st July 2006, 02:37 PM
Over the next couple of weeks, i would like the community as a whole to estblish a series of FAQ's related to arcade technical and repairs. I thought that power supplies would be a good place to start and if other want to start on Monitors etc then feel free to. Alot of this information is already posted on the site in various locations, but it would be good to have a central point of reference to direct new members to. Below is a priliminary FAQ that i will amend. Feel free to post your own questions and answers, or just questions.

The Big Bad Power Supply FAQ.

Many people underestimate the importance of a good quality power supply. In my time as a computer technician, many hardware faults were a direct consequence of a poor or failing power supply; arcade cab’s are no different in this respect.

Some boards/pcb’s are fussier than others when it comes to power supplies, especially late model Sega and Namco boards, but for the most part pcb’s will run just fine up until the power supply gives out. Some boards may act spasmodically, i.e. your game will often freeze or reset, or in worst case scenario’s your power supply may be responsible for destroying your pcb’s.

In this FAQ, we as a community will endeavour to answer all frequently asked questions relating to power supplies. As usual, the normal disclaimers apply. If you are uncomfortable with adjusting/troubleshooting your power supply issues then please ask a professional. The advice contained within this FAQ is always evolving to provide the best possible answers.

So here we go!

How can I tell if I have a faulty power supply?

What voltages does my board use?

This will vary from board to board, but basically if you have a JAMMA board then it will require 12V, 5V, and occasionally -5V. 12V is mainly used for sound and 5V for the logic functions of the board. -5V is used on older boards and is also used to run the light globe in your coin mechanism (assuming you have one).

Modern non-JAMMA boards often require an additional 3.3V line. These boards come under the classification of JVS or JAMMA+. The best examples of these are the Sega Naomi, Model 1, Model 2, Model 3 and Namco System 246, although there are many more. The majority of these boards will use custom power connectors.

All JAMMA and JVS voltages are DC (direct current).

Board pre-dating JAMMA can vary wildly. Some even use AC (alternating current). If your board does not use a Jamma connector then consult schematics or the games manual to find out what your board requires.

What voltages do I need?

As already mentioned, the main Jamma voltages are 12V and 5V, with some boards requiring -5V also. Depending on the application, an AT or ATX computer power supply can be used instead of an arcade psu, but this is not recommended for several reasons. First, computer power supplies cannot be adjusted or fine tuned like regular power supplies. Secondly, some computer power supplies will not even start unless they have enough of a load on the 5V line and probably most importantly PC power supplies have the ability to deliver a massive shock if you mess something up.

What are Volts, Amps, Ground and Watts?

What is a Multimeter?

What power supply should I buy?

How do I adjust my power supply?

What else does the power supply operate inside my cab?

Depending on the type of cab you have got, the power supply can be used to power many of the interals with the exception of the tube and fluro's (if you have one of course). The most common peripheral to be powered by the machines psu other than the actual gameboard is the coin mech followed by complex input peripherals such as optical joysticks or trackballs etc. Other items that are powered by the psu are...

Ticket Machines
EL Panels (electro luminesant) -found in some neo geo's.
Optical Sticks
Credit Boards
Optical Guns
Video Converters

When trying to find a suitable replacement power supply, you should find out which of these items you have and also see how power hungry these items are.

My power supply is making noises! What is going on?

What does the "FG" post on my power supply do?

The FG post is used to help counteract any monitor interference you are getting as a result of poor grounding. E.g. when i run my naomi gd rom, the interference caused by the gd rom unit causes lines to roll through my monitor. By bridging your ground post to the FG post, you can nearly always eliminate this type of interference. A tutorial can be found here (http://www.killercabs.com/tutorials/Putting_The_Jumper_In_To_Eliminate_Monitor_Interfe rence.pdf)

21st July 2006, 05:26 PM

As someone who has blown up two power supplies becuase of a shorted coin counter, I have learnt the hard way why you need to check your wiring for shorts prior to installing a pwoer supply.

All you need is a contuinty test, a light and some patience to trace wires, partiuclarly strays to see where they ae going and what they may be attached to.

24th September 2006, 01:58 PM
You also need to check for ac ripple on the linear supplies.A large ripple is usually a sign that the smoothing caps are bad

24th September 2006, 02:20 PM
Was just helping the SRK kids with a Multimeter / multitester introduction not moments ago.

Wikipedia has a good slog of information on them:

As well as a link to a brief guide on how to use them and what results to expect:

14th October 2006, 12:51 AM
How do I test my PSU? More specifically, how do I test -5V...Here's what I get on my PSU...

GND & +5V = 5.10V = good
GND & +12V = 11.90V = good
GND & -5V = 500mV = WTF?!?

Either there is something drastically wrong with the way I am testing -5V or my PSU is drunk.

14th October 2006, 01:05 AM
How do I test my PSU? More specifically, how do I test -5V...Here's what I get on my PSU...

GND & +5V = 5.10V = good
GND & +12V = 11.90V = good
GND & -5V = 500mV = WTF?!?

Either there is something drastically wrong with the way I am testing -5V or my PSU is drunk.

Shit, I have never had that happen before. Try putting ground on -5 and pos on ground.

14th October 2006, 01:16 PM
OK testing GND & -5V today gives flat 0. Tried the probes the other way around (as suggested) but still 0V.

So I test my cocktail and get -4.5V across GND & -5V. So maybe my upright's PSU is not doing the do. Or maybe its because the upright has -5V wired and the cocktail doesnt. Maybe there is a short somewhere (or the chassis is affecting the result). I will disconnect the -5V and try again.
OK. I disconnected the upright's PSU and still get the same result :( Dodgy or not wired internally? Either way its why older shite aint working.
Maybe I will swap them as the cocktail is not in use, doesnt have -5V wired, and is gonna be a MAME2JAMMA cab one day anyways.

27th July 2015, 02:41 AM
Shit, I have never had that happen before. Try putting ground on -5 and pos on ground.

A lot of the cheap arcade PSU's don't have -5 internally, when you order from Chinese suppliers you normally have to specify if you want -5v because most boards don't need it.

It will always have the terminal on the outside as normal but nothing connected inside and all the components needed are missing, sounds like this is what you have,

14th April 2017, 02:04 AM
Necro Bump!

If you wish to try to repair your switching power supplies, here's a guide (http://newlifegames.com/nlg/index.php?topic=1393.0) I have in my repair logs.