Sangean's original User and Service Manuals
Two things that are essential for anyone using and servicing complex radio equipment are the manufacturer's user and service manuals. They contain specifications, information regarding use and upkeep of the equipment, and general methods of troubleshooting. The engineers who designed the equipment give official procedures for servicing the radio. However, more in depth information builds on the internet as more users become familiar and proficient at tweaks and mods for the ATS-909 / DX-398. It all starts with manuals, a schematic, some solder, and a dream...
Here is the ATS-909 / DX-398 User Manual, containing specifcations and basic instructions for operating this fine shortwave radio.
For more in depth technical information, use the Sangean ATS-909 / DX-398 Service Manual.