Component Failure-Mode Cheat Sheet
How each part fails — and how to confirm it
▣Circuit Card Academy
| Component | How it fails | How to confirm |
|---|---|---|
| Aluminum electrolytic | Age and heat can reduce capacitance and raise ESR; short circuits are also possible. | Inspect, then verify capacitance, ESR or leakage using the specified isolated test; ripple alone does not identify a capacitor. |
| Tantalum | Fails SHORT, sometimes ignites. A burnt crater on the board is often a tantalum. | Ohms / diode-test to ground reads near 0 Ω; visible char. Confirm by lifting a leg. |
| MLCC ceramic | Cracks from board flex or thermal shock → intermittent or short. Crack can be invisible. | Classic 'rail reads ~0.5 Ω to ground'. Find by mV-gradient / thermal hunt, then lift to confirm. |
| MOSFET | Fails drain-source SHORT typically. Gate oxide is ESD-fragile. | Identify device topology and protection structures from the datasheet. A body diode may be expected; gate charging and parallel paths can mislead. |
| TVS diode | Can fail short, open or leaky; a transient is a possible cause, not automatically proven. | Identify unidirectional/bidirectional type. Isolate to distinguish parallel shorts. Diode mode does not verify clamping performance. |
| Via | Cracked plated barrel from thermal cycling → intermittent: works cold, fails hot (or inverse), flex-sensitive. | Localize continuity changes using an approved, de-energized environmental/mechanical test within assembly limits. |
| Connector | Bent or recessed pins, fretting corrosion, damaged joints or cable strain. | Visual under magnification; continuity pin-to-solder-tail; mV-drop under load on suspect contacts. |
| Crystal / oscillator | Mechanically fragile — a dropped board with a dead clock is a prime suspect. | Verify setup, probe loading, supply, enable and specified clock test point; a flatline alone does not prove the crystal failed. |
| Resistor | Mostly fails OPEN or drifts HIGH, usually from an overload elsewhere — often the victim of a short. | Verify contact, energy state, part identity and meter setup; confirm with an authorized isolated measurement. |
| Solder joint | Cracks, insufficient/excess solder, poor wetting or misplaced parts; appearance depends on alloy and process. | Inspect against the controlled acceptance criteria and electrically localize. Reflow recovery alone does not establish the mechanism. |
Generic engineering reference. Always confirm a suspect part out-of-circuit (lift a leg) or against a golden board before replacing it; the solder joint, via and trace are suspects of equal rank with the component.