Capacitor Plague

The capacitor plague refers to an era (roughly 1999 to 2007) when large numbers of aluminum electrolytic capacitors failed prematurely because of a defective electrolyte formulation. The flawed electrolyte lacked the chemistry needed to keep its pH stable over time, so it corroded the capacitor internals and generated gas. Affected capacitors bulge at the top, vent, or leak electrolyte, and the equipment they sit in becomes unstable or stops working long before its expected service life.

The role of ESR

Equivalent series resistance (ESR) is the unwanted internal resistance of a capacitor. As an electrolytic capacitor degrades, electrolyte dries out or vaporizes, capacitance falls below its rated value, and ESR climbs sharply. High ESR causes the capacitor to self-heat under ripple current, which accelerates further degradation, a runaway loop that ends in venting. The vast majority of electrolytic field failures are tied to rising ESR rather than dead shorts, which is why an ESR meter is a core diagnostic tool.

What to look for in repair

Visually inspect electrolytic capacitors for a domed or split top, crusty residue around the base, or a popped vent. Even capacitors that look fine can be marginal, so measuring ESR in circuit and replacing suspect units with quality low-ESR parts is the reliable fix. On power-supply and control boards in mining gear, aging electrolytics are a frequent root cause of brownouts, restarts, and erratic behavior.

For related component-level diagnostics, see our entries on ESR testing and thermal fatigue.