Field Failure Modes by Component#

How components actually fail in the field, and how those failures present at the bench. This is not about how components work or how to characterize them on a curve tracer — for test procedures and instrument settings, see Component Testing. This page is symptom-driven: what shows up at the bench, what to suspect, how to confirm, and where to go next.

Electrolytic Capacitors#

The most failure-prone passive component. Electrolytics have a liquid electrolyte that dries out over time, and the failure rate increases dramatically with temperature.

Symptom	Suspect	Quick confirmation	Next step
Increased ripple on a DC rail	ESR rise from dry-out	ESR meter — compare to published specs	Replace the cap
Decoupling degraded, downstream IC misbehaving	ESR rise or capacitance loss	ESR meter or substitution test	Replace and retest the downstream circuit
Rail drops to zero or fuse blows	Shorted cap (dielectric breakdown)	Remove cap, check if short clears	Replace; check for overvoltage cause
Brown/orange residue on PCB near cap	Leaking electrolyte	Visual — it’s leaking	Replace cap, clean residue (it’s corrosive), inspect nearby traces

Visual signs: Bulging top vent, leaking residue, discolored PCB underneath, cap sitting crooked (pushed up by internal pressure).

Testing detail: A basic capacitance meter won’t catch the most common failure (ESR rise). This requires an ESR meter or an LCR meter that reports ESR at the right frequency. See ESR, Leakage & Gain.

Rule of thumb: In consumer electronics more than 5–10 years old, electrolytics near heat sources (voltage regulators, power transistors) are the first suspect.

Ceramic Capacitors#

Usually reliable, but they have one spectacular failure mode.

Symptom	Suspect	Quick confirmation	Next step
Rail shorted to ground, upstream protection trips	Cracked ceramic → internal short	Remove ceramic caps one at a time near the fault; short clears when the cracked one is removed	Replace; investigate mechanical stress source
Subtle capacitance loss on high-K dielectric (X5R/X7R)	DC bias derating — not a field failure, a design issue	Measure capacitance at operating voltage vs. at zero bias	Redesign with lower-K dielectric or larger package

How cracks happen: Board flex during assembly, thermal shock, rough handling, or press-fit connectors nearby. Visually, a hairline crack may be visible on the top surface, but often the crack is hidden underneath.

Voltage Regulators#

Linear and switching regulators are common failure points because they handle the full load current and dissipate power.

Symptom	Suspect	Quick confirmation	Next step
No output voltage	Input missing, enable pin in wrong state, or regulator dead	Measure input pin, enable pin, and output pin voltages	If input and enable are correct but output is zero → replace regulator
Output low (e.g., 2.8 V instead of 3.3 V)	Overcurrent (regulator in current limit) or dropout (input too close to output for LDO)	Check load current; check Vin − Vout margin	Reduce load or fix downstream short; ensure adequate input voltage
Output oscillating	Missing or wrong output capacitor, ESR out of range for LDO stability	Scope the output; check cap values and ESR against datasheet	Replace output cap with correct value and type
Output voltage correct but noisy	Switching noise (normal for DC-DC, but excessive), or input noise coupling through	Scope with short ground lead; compare to datasheet ripple specs	Add/improve input and output filtering
Regulator extremely hot	Excessive load, shorted output, or high dropout dissipation	Measure current draw; check for downstream shorts	Fix the load problem; don’t just add a heatsink to a fault

Check first: Input voltage at the regulator pin (not just “somewhere on the board”). Enable/shutdown pin state. Output voltage at the regulator pin and at the load.

Transistors (BJT and MOSFET)#

Symptom	Suspect	Quick confirmation	Next step
Circuit stuck high or low regardless of control signal	BJT shorted C-E or C-B (overcurrent/avalanche)	Diode-check: reads near zero in both directions across shorted junction	Replace; check what caused the overcurrent
Circuit open — no current flowing through transistor path	BJT or MOSFET open (bond wire or die crack)	Diode-check: reads open on all junctions	Replace
MOSFET won’t turn off, drain-source always conducting	Gate oxide breakdown or D-S short from overcurrent	Diode-check D-S; check gate threshold voltage	Replace; investigate ESD or Vgs overvoltage source
MOSFET switching but running hotter than expected	Increased Rds(on) from partial damage	Measure Rds(on) or compare thermal behavior to a known-good part	Replace — partial damage gets worse

Testing: Diode check across all terminal pairs (gate-source, gate-drain, drain-source, both directions). Compare readings to what the device type should show. See Dead or Alive?

Resistors#

Resistors are generally reliable, but they fail under sustained stress.

Symptom	Suspect	Quick confirmation	Next step
Circuit open, charred or cracked component visible	Resistor open from overcurrent — burned through	Resistance measurement: reads open or megohms	Replace; investigate what caused the overcurrent
Bias point or voltage divider slightly off	Value drift from chronic overheating	Measure resistance, compare to marked value and schematic	Replace; check power dissipation in the design
Intermittent behavior, especially with vibration or temperature change	Solder joint failure (the resistor itself is fine)	Reflow the joints; check for cracks under magnification	Reflow or replace

The sneaky one: A resistor that’s drifted 20% doesn’t look broken, and a quick measurement might seem “close enough.” Always compare to the marked value (color code or package markings) and to the schematic.

Connectors#

Connectors are mechanical components, and mechanical components wear.

Symptom	Suspect	Quick confirmation	Next step
Intermittent connection, position-sensitive	Corroded pins or worn contact springs	Visual inspection (green/white deposits); wiggle test with continuity meter	Clean with contact cleaner, or replace
Wire pulls free with gentle tension	Backed-out terminal — not fully seated in housing	Pull test on each wire	Reseat or re-crimp the terminal
Intermittent on a board-mount connector, especially one that sees cable insertion/removal	Cracked solder joint from mechanical stress	Magnification; reflow and see if behavior changes	Reflow or replace the connector

ICs#

IC failures are usually diagnosed by exclusion — verify everything around the IC first.

Step	What to check	If wrong
1	All supply pins — correct voltage, decoupled, no excessive ripple	Fix the power problem
2	Control inputs — reset, enable, chip-select at correct levels	Fix the upstream driver or pull-up/pull-down
3	Clock (if applicable) — correct frequency, clean edges	Fix clock source
4	Data/signal inputs — correct levels, timing, protocol	Fix the upstream source
5	All inputs correct, outputs still wrong	Suspect the IC itself

Don’t jump to “bad IC” too quickly. An IC with incorrect inputs produces incorrect outputs, and the problem is upstream. Most “bad IC” diagnoses in hobbyist debugging turn out to be bad power, missing pull-ups, or wrong configuration.

Quick Reference#

Component	Common field failure	How it presents	First move
Electrolytic cap	ESR rise / dry-out	Increased ripple, poor decoupling	ESR meter
Ceramic cap	Cracked → short	Rail drops to zero, upstream protection trips	Remove caps one at a time
Voltage regulator	Overcurrent / thermal death	Wrong output voltage or no output	Measure Vin / Vout / enable
BJT	Shorted junction	Circuit stuck high or low	Diode check all junctions
MOSFET	Gate oxide / D-S short	Won’t switch off, always conducting	Diode check, gate threshold
Resistor	Open from overcurrent	Open circuit, charred body	Resistance measurement
Connector	Corroded / worn	Intermittent, position-sensitive	Wiggle test, continuity
IC	Various	Wrong outputs despite correct inputs	Verify all inputs first

In Practice#

An IC that works for weeks and then fails without any change in operating conditions often indicates cumulative downward damage — electromigration, oxide degradation, or solder joint fatigue that has been progressing since initial deployment, finally reaching the threshold where the circuit can no longer function.
A gradually increasing error rate over weeks or months often indicates aging at the primitive level — a solder joint developing a fatigue crack, a capacitor losing capacitance, a connector contact corroding — propagating upward through the hierarchy as a gradually worsening performance metric at the system level.