The +5V test points are clearly marked on both boards... there should be (at least) two of them per board. The GND test points are marked as well.
The AR-II's are the power supply boards, they're on the back side of the cabinet (just below the back door). There is a small dial on them that you can adjust +5V with... I don't have a picture of that, but there should be some pictures of them online somewhere.
Before you test/adjust any voltage, clean the edge connectors first.