Recommended board: Basic.

The 7800 uses a 74LS08 to combine the video signals from TIA and Maria and discrete wires will be needed to get the combined signals to the UAV.

-^Cro§Bow^- has done some excellent videos and an install guide.

UAV_Installation_A7800.pdf

Installing an Audio Companion board:

The Audio Companion board will mix the 7800's TIA audio with audio from a cartridge at the appropriate levels without requiring any modifications to the existing circuit. RF audio will continue to work as before.

1. Locate C16 and solder the Audio Companion board across its leads with ground (G) toward the front. Apply the soldering iron to both the capacitor lead and the large pads at the bottom of the board while applying solder until they flow together. This will provide power and hold the AC in place.
2. Solder a wire from input iA (the first pad at the top from the back) to the front pad of R6 (18K). This is the resistor to the left of the RF audio choke on NTSC 7800's.
3. Solder a wire from input iC (the third pad at the top from the back) to the front pad of R5 (6.8K). This is the resistor next to R6 on NTSC 7800's.
4. Connect the audio out wire to the last pad on the Audio Companion marked out. If you're using a coaxial wire, you can connect ground to the front pad of the unused spot for C18.

Carefully check your work against the pictures before powering the system. Route cables carefully out of the shielding during reassembly.