I have cleaned the exterior and tested this unit.  Everything appears to be working.  I am including the original power source.  However, you will need to supply your own RCA/Coaxial Game Switch.  This unit plays on channel 3 or 4 analog.  The joysticks would benefit from an internal cleaning of the contacts.  All motion is detected, but it is a little jerky.  The joysticks feel great and video looks good.

To serve the ball, both joysticks need to push the button at the same time.

The Odyssey 4000 (Model 7511) dedicated console was released in 1977. Based around the AY-3-8600 single-chip design, the 4000 features a total of seven games (Tennis, Hockey, Volleyball, Basketball, Knockout, Tank, and Helicopter) that with variations can be expanded to twenty-four different gaming experiences.

The unit allows up to four players and includes a Practice mode for solo-play against the computer. As with the 3000, the 4000 offers a skill switch for novice, semi-pro, and professional skill levels.

Additional features include automatic serve, variable ball speeds, and a pause button.[4]:24-25 Unlike the Odyssey 3000, the 4000 featured detachable joysticks. The AY-3-8615 chip enabled the Odyssey 4000 to display color instead of black and white graphics. The 4000 is powered by an included AC adapter.