measure the terminals at the power supply for +5 VDC, then measure the power connector that plugs into the board to make sure I am getting the same reading
well, if you measure "before" the connector on the wire side(with extensions on your probes to stick down into the ends of the pin inside the connector to get the measurement), that will tell you what the power supply is putting out. i measure there cause its right next to the next measurement location which is "after" the connector, on the game PCB. one can easily find the ground rail and the +5 volts DC without any extensions for your probe. i use alligator clips. that measurement will tell you what the board is actually getting after all the wiring, connectors, etc.
you dont really need to do the first test but i do it to tell me what kind of condition the pins are in just for fun. i like to see what voltage drop i am getting through the connector. i have a crimp tool and pins and i like to replace them as necessary.
for instance you might have a reading of 5.20 before the connector and a reading of 4.80 on the PCB, which might not be enough to run the game. that voltage drop tells you you either have weak pins, oxidized pins or both or some other problem like a bad wire etc. on the other hand you might have a reading of 5.20 before the connector and 5.19 on the game PCB which tells you thats not much voltage drop but is it enough to run the game? try turning up the voltage but dont go over 5.35 as the chips dont like that high a voltage and could be damaged.
if you have alligator clips for your probes you can then adjust your +5 volts with your free hand while your probe is clipped to something in the ground rail and +5 volt rail like a capacitor leg or one end of a resistor, whatever you can find. sometimes i cant find both my alligator clips and i just use the one on the ground leg and i hold my red probe with my other hand while adjusting knob on the PS. also leaves me a hand to quickly shut game off for any reason to keep from damaging something or if somethings not right.
*remember* logic ground is different from earth ground. you can put your ground probe on the GND terminal of the power supply too. you can get screwy readings if you have your gnd probe on earth ground so dont make that mistake.