While switching power supplies are the standard in newer arcade games, classics such as Ms. Pac Man and Galaga originally had non-switching, linear power supplies that can be quite intimidating at first glance. These classic (or old school) power supplies usually look like a brick located at the bottom of your cabinet and can be difficult to work with due to years of wear and tear. In this post, we will discuss how to check the voltage coming out of your classic power supply as well as how to check the voltage on your board at the harness connection.

Checking A Classic Power Supply

First off, we want to identify where our classic power supply is in our cabinet. These power supplies are typically located at the bottom of the cabinet and resemble a brick-like structure. They should have AC voltage coming into of the bottom of one side either directly from the wall or from an AC filter. The bottom of the other side should contain the DC voltages that go out to the board and other cabinet parts such as coin lights. Be careful not to mistake your isolation transformer with your power supply. Isolation transformers can look very similar to classic power supplies except for the fact that they only use AC voltage and typically just run the power to the monitor. They usually have two wires coming into the bottom for AC input from the wall or AC filter and two coming out of the top for AC output to the monitor.

If you just see one brick-like structure in the bottom of you cabinet it could be that you have a dual power supply/isolation transformer unit. If this is the case then the bottom of both sides should have AC input lines with the top of one side putting out DC voltage to the board and the top of the other side putting out AC voltage to the monitor. While these dual units are not as common, they are certainly something to be aware of in case you run across one.

Once we have located the power supply in our cabinet, we can begin the process of checking the voltages. Let’s start off by setting our multimeter to DC voltage just like we would if we were checking a standard switching power supply. Now we must identify which of our contact points are grounds and which ones hold voltages. Most of these power supplies were labeled at one time or another, however, age and normal wear and tear usually leave them in an unreadable state. Instead of just randomly touching our contact points without a clue, we recommend placing the black probe of your multimeter on the AC ground coming from the wall. The AC ground is usually easier to located than the DC ground and allows us to check the contact points safely with our red probe. Obviously if we touch a contact point on our power supply and the multimeter doesn’t indicate any voltage then we are probably touching a ground point.

Something to keep in mind when checking our classic power supply is that not all of them put out the same voltage. For example, a Ms. Pac Man usually puts out 7 VDC instead of the standard 5 VDC because of the other cabinet parts that use that particular line. If you find that your power supply is giving off higher voltage than what the manual for the game shows then you might try checking the voltage where the board connects to the harness. This can usually be accomplished by finding the ground and DC voltage pins on your harness (via your manual) and placing your multimeter probes on these points. Your board might have easily accessible contact points that you can place your probes on for testing. Whatever way you decide to check the voltage going to your board, performing this check allows you to make sure your board is not just getting power but the correct voltage.

You might also notice some fuses located in the bottom of your arcade cabinet around the power supply. While you can certainly check these in the traditional manner that we discuss in our post on Checking Fuses With A Multimeter, you can also check them with the game on by placing your black probe on a ground point and the red probe on the other side of the fuse. If voltage is flowing through the fuse then you know that it is good. Also, make sure that you are careful when working with an arcade game that’s plugged in. Always take the necessary measures to make sure you are safe when working in these situations.

Most of the arcade games that people consider classics such as Ms. Pac Man and Galaga did not have the benefit of switching power supplies when they were produced. As such, having the skills to check a classic power supply can be a very valuable as you work on these older arcade games. Please let us know if you have any questions or suggestions by leaving them in the comments section below.