While a single comprehensive "service manual" containing full component-level schematics is not publicly hosted by the manufacturer, essential technical documentation for the QYT KT-7900D
The aluminum chassis acts as the primary heatsink for the RF power components. Never transmit for more than a few seconds while the main PCB is removed from the metal casing, or you risk burning out the final amplifier stage. qyt kt-7900d service manual
The service manual details the inner workings of the KT-7900D. qyt kt-7900d service manual