A common problem with external hard drives that have a built-in USB controller is that this controller is actually two devices in one, meaning… , two controllers: one SATA and the other USB. Due to improper use (voltage/current surges), the USB part of the controller fails, causing the disk to be undetectable and considered damaged. In such cases, data recovery does not even require a donor controller — the SATA connector is simply soldered with a flexible cable to the existing controller, and the disk is connected directly to the computer for data extraction.