Autopsy:

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You can found Parts list and Schematics here

from wiki.intellivision.us Homepage:

The Intellivision directly generates composite video using the AY-3-8915 Color Processor and a set of resistors. This video gets fed to the ASTEC UM1285-8 video modulator for conversion to RF for display on a television set. It is possible to tap this composite video directly to avoid the distortion and static associated with RF modulation and demodulation. On older units, the RF modulator can decay rather noticeably, leading to very low quality video.

Typical composite video inputs have an input impedance of 75Ω. In contrast, the composite signal generated by the Intellivision has a very high output impedance. (We estimate the output impedance is around 2KΩ.) Tapping this output and feeding it directly into a typical composite monitor does not work. (It will work if your monitor has a “high impedance” input, but such monitors are atypical.) Thus, an amplifier/impedance matching circuit is necessary.

It is also possible to tap the audio the Intellivision generates. The audio output by the Intellivision is nearly directly suitable for feeding line-level inputs on most AV equipment. All that’s required is a coupling capacitor.

The modification should work equally well on all Intellivision variants, including the Intellivision 1, Intellivision 2, the various rebranded units (Sears, Tandy), and the later INTV releases.

source: wiki.intellivision.us