Once extracted, you will likely find a PDF manual containing:
Schematics for the amplifier, tuner, and DVD sections.
Because .rar files are compressed, you need specific software to open them. Use 7-Zip (free/open-source) or WinRAR . Right-click the GN88D.rar file. Select "Extract Here" or "Extract to GN88D/" . For Mac/Mobile: Use apps like Unzip One or iZip .