The QYT KT-7900D is a dual-band amateur radio transceiver. If you're looking for the service manual, here are some steps to help you find it:
For detailed board-level repairs, hobbyist forums often share unofficial schematics or partial circuit diagrams. Platforms like Radioscanner.ru (which hosts schematics for the similar KT-8900) or VRTP.ru are valuable for cross-referencing components like the Beken chip or power regulators.