Fried TVS diode on PCB?

A fried TVS (Transient Voltage Suppression) diode on a PCB usually indicates that the circuit experienced a voltage surge, reverse-polarity event, or another electrical fault. A TVS diode is designed to protect sensitive components by clamping excessive voltage. When the surge is severe, the diode can fail, often becoming shorted or visibly burned.

Common Signs of a Failed TVS Diode

A damaged TVS diode may show visible cracks, discoloration, burn marks, or melted packaging. However, some failed diodes look completely normal.

A multimeter can help identify a shorted TVS diode. With the PCB powered off and disconnected, measure resistance across the diode. A very low resistance reading in both directions may indicate that the diode has failed short-circuit.

Why Does a TVS Diode Fail?

Several conditions can damage a TVS diode:

Incorrect power supply voltage

Reverse-polarity connection

Electrical surge or spike

Lightning-related surge

Faulty power adapter

Short circuit elsewhere in the system

Excessive continuous voltage

Sometimes the TVS diode is not the original cause of the failure. It may have sacrificed itself while protecting another component.

Should You Replace the Diode?

Do not simply remove the burned diode and continue using the PCB. Without the protection device, another voltage surge could damage more expensive components.

If replacement is appropriate, match the original diode's specifications, including its standoff voltage, clamping characteristics, power rating, polarity, and package type. Using an incorrect TVS diode can provide inadequate protection or cause unwanted circuit behavior.

Check for Other Damage

Before installing a replacement, inspect the surrounding components and PCB traces. Check fuses, resistors, capacitors, MOSFETs, voltage regulators, connectors, and power-input circuitry for signs of damage.

If the replacement TVS diode immediately becomes hot or fails again when power is applied, there may be an underlying short circuit or excessive input voltage.

Final Thoughts

A fried TVS diode is often a warning that the PCB experienced an electrical event. Replacing the diode without identifying the original cause can result in repeated failure. If the board contains important data or expensive electronics, proper diagnosis is safer than repeatedly applying power.

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