"Where is the short?" she murmured. According to the schematic, the main power rail (VIN) spread like capillaries to three major components: the charging IC (PU301), the main voltage regulator for the 3V/5V standby rails (PU401), and—infamously—a cluster of ceramic capacitors (PC401, PC402, PC403) near the standby regulator.
Following the "Power Tree" on page 17, she traced the main power rail from the DC jack. The first stop was a pair of MOSFETs, PQ301 and PQ302, known as the isolation circuit. Their job was to protect the board from reverse polarity or overvoltage. ldb-2 mb 11232-1 schematic
To a layperson, it was just a green slab of fiberglass and copper. To Mira, it was a topographical map of a city—with power rails as highways, data lines as streets, and tiny black ICs as buildings. This board, often found in the Lenovo G580 or similar series, had a reputation. It was known for a "ghost in the machine": a fault that appeared, disappeared, and reappeared without warning. "Where is the short