Now that you know what kind of power brick you have and have pulled the schematics for it, now it’s time to do some basic troubleshooting. Take a close look on, around, and under your power brick. Look for anything that doesn’t look right such as burnt components, cut wires, wires pulled away from their terminations, missing Power Selector, missing fuses (including pulling the main fuse), or any Molex connectors that should be attached but aren’t.
You will need you digital multimeter for this step. First we want to check all of the fuses and make sure they’re ok. Set your multimeter to ‘continuity test’ and make sure your game is UNPLUGGED FROM THE WALL SOCKET. If your brick has the paper shield covering the fuse block, carefully remove it. Next, probe across each fuse in the fuse block as in Figure 1 and make sure there’s continuity. Your meter should probably ‘beep’.
Figure 1: Continuity Test of Fuses
If you find one or more bad fuses you must replace them. The fuse voltage and amperage ratings are listed on the fuse block. It is highly recommended you use an exact rating replacement! Using anything else would mean either you’re not allowing enough current to flow in the circuit and the fuse will blow under normal operation, or you’re allowing too much current to flow and you’re allowing the circuit fault downstream to destroy something.
Next, unscrew and pull the main fuse. Check for continuity just like you did before. If it’s bad, replace it.
If you found just one bad fuse, you could now try to operate the game and see what happens. Like other electronic components, fuses just sometimes go bad. If you find more than one bad fuse then chances are it’s not just the fuses that are bad. But in most cases the very worst that will happen is you’ll blow the new fuses.
Molex Connector Pinouts
Before we tackle the next section on testing voltages, we first need to understand how Molex connectors are pinned. There’s two sides to a connection pair – male and female. The male side has wire terminations that are pins, primarily, while the female side has sockets as wire terminations. If you look ahead to the Molex connector in Figure 3, you can see that the connector has female socket terminations in all but two positions, so we can refer to this end as female. It is important to note that pin numbering for male and female connectors are exactly mirrored from each other. What I present here are the female pin numberings. To get the male numberings, just mirror the female numberings.
If your eyes are still good enough you can also look at the insertion side of the connector and find the pin numbers stamped by each pin. Figure 2 shows pinnings for some common Molex connectors while looking into the female end of the connector.
Figure 2: Female Molex Pinouts
In this step we will be testing the voltage outputs from the brick. Take a look at your schematic and find the reference designators for all of the connectors. These refer to the Molex connectors on your power brick. For example, on my schematic the 15-pin connector J5 refers to the Molex connector J5 on the power brick.
Figure 3: Molex Connector J5
Look closely and you’ll find that the reference designators are stamped next to each Molex connector on the brick. We want to find the Molex connector(s) that give voltages out of the brick. In this case we’ve found J5.
If you removed the power brick from the game, re-install it and re-connect all of the Molex connectors except for the voltage output connector J5. Notice that we have both AC and DC voltage outputs here. No matter what type of brick you have, there are two main voltages that the Audio Regulator (AR) board uses to power your main CPU board: 10.6VDC (or 10.3VDC) and 36VAC. The rest of the voltages are used for things other than the CPU like the marquee light, fans, monitor, etc. We want to make sure that all of the voltages are good, but those two in particular.
Power your game on and set your multimeter to measure DC volts. Carefully stick the positive (red) lead of your multimeter into one of the 10.6VDC female pins. Then stick the ground (black) lead into one of the GND female pins. You should measure close to 10.3VDC. The voltage is unregulated so it might not be exact. If your reading is within about 20% then it should be ok. There’s no need to test all three of the 10.3VDC outputs since they are all tied together.
Figure 4: Testing Voltages
Remove the test leads from J5 and set your meter to measure AC volts. Now before we measure AC volts we need to review briefly how a transformer works. A transformer performs two basic functions. First, it is able to change the output AC voltage less-than, greater-than, or the same as the input AC voltage. Second, it serves to isolate the output AC from the input AC so as to move the relative ground where it needs to be. The main thing to remember is that a transformer center-tap will be at half the AC voltage of the two ends. Let’s take our Centipede transformer as an example.
Figure 4: Centipede Transformer Schematic
Probing between pins 13 and 15 in this circuit yields 60 Volts AC. Probing between pins 13 and 14, or between 14 and 15 should yield about 30 Volts AC. Continue testing all of the AC voltages on the voltage output connector on your power brick. Refer to your schematic to make sure you cover all of the voltages. If you find that pins are missing from the Molex connector then don’t worry about testing those voltages.
If all of the voltages check out then it’s time to move on to testing the Audio Regulator (AR) board.