If the power brick is the catfish then the Audio/Regulator might be the barnacle. Youíll find it attached vertically behind the brick by the coin bucket. Its notable features include bulbous capacitors and a large heatsink in the middle. Itís also the more troublesome of the two.
The Audio/Regulator (or AR for short) was produced in three versions, AR-I, AR-II, and AR-III, and several revisions. The AR-I was the earliest and used for a good many Atari black and white games. The AR-II was designed to be a superset of the AR-I, adding a few new features while still being pin-compatible with the AR-I. After that Atari came to their senses and produced the AR-III which was a complete re-design from the two previous and not at all pin-compatible.
If all of the voltages check out then itís time to move on to testing the Audio Regulator (AR) board.