The secondary side converts transformer energy into regulated DC outputs. Faults here can produce missing voltage, low voltage, excessive ripple, protection cycling or a supply that refuses to start.
Check output rails with power removed
Measure resistance to secondary ground and compare the rails. A very low resistance may indicate a shorted rectifier, capacitor, load IC or downstream circuit, but expected values depend on the design.
Test secondary rectifiers
Schottky diodes and synchronous rectification MOSFETs are common failure points. Use diode-mode and resistance measurements to identify obvious shorts while remembering that parallel circuit paths can affect in-circuit readings.
Inspect output capacitors
Electrolytic capacitors can lose capacitance or develop high ESR without obvious swelling. Excessive ripple, unstable regulation and startup problems can all be related to degraded filtering.
Evaluate feedback and loading
If output components appear healthy, determine whether the feedback network is reporting the correct voltage and whether an external load is forcing the supply into protection. Disconnecting loads should only be done when the circuit architecture is understood.
Compare SMPS readings systematically.
BoardIQ helps organize output rails, reference values and diagnostic decisions across primary and secondary stages.
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