Bad capacitors: visual clues, ESR, and replacement

Practical capacitor notes for laptop and desktop boards (original NLCRC wording). Visual / smell clues - Bulging tops, crusty electrolyte, or a sweet/acid smell near VRMs are classic failures — especially older motherboards and GPU cards. - Absence of bulging does not mean healthy: high ESR caps can look normal and still collapse under load. Measurement - Use an ESR meter or a capable LCR tool out of circuit when possible. In-circuit readings are rough guides only. - Compare against nearby identical caps on the same rail. Replacement - Match capacitance, voltage rating (equal or higher), and prefer low-ESR types on CPU/GPU VRM outputs. - Mind polarity on electrolytics. After rework, clean flux and re-check the rail under load. If the board also has secondary shorts on MOSFETs or PWM controllers, fixing caps alone will not bring the rail back — continue with power-rail triage.