Three types of Odyssey models have been produced: I) 2800, 2) 2810-2815 and 3) 2820-2823. The model and serial number are located at the rear or bottom of the Odyssey chassis. Except for 2800, a typical number might read: 2813-0490. For model 2800, the first two digits of the serial number denote the model, such as: 28490. Listed below are the board identification numbers for each model; they will be referenced in the service manual by model number for easy identification. Model Changes The Odyssey has undergone major cosmetic and electrical changes since its original production in 1972, however, the functional capabilities have remained virtually unchanged. The following are the most noticeable physical differences among models: MODEL 2800 Black and white face panel (some later models have black and gold face panels). Pitch Bend knob No Factory installed interface jacks. Wrap around vinyl bottom cover. MODEL 2810-2813 Black and gold face panel. New style power switch. Factory installed interface jacks* Pitch Bend knob. (Some later models have PPC.) Wrap around vinyl bottom cover. MODEL 2820-2823 (current model, Odyssey '78) Black and orange face panel. Steel chassis Leather endblocks - PPC The major electrical changes found in the Odyssey-II as compared to the Odyssey-I are: 1. Uses 24db/octave filter in place of 12db/? octave. 2. Improved VCO design for better tracking# and stability. 3. Improved power supply regulation. 4. Improved keyboard current source for CV generation. 5. Improved S/H memory circuit design.