Fault

Protection light on

Overcurrent, thermal and feedback diagnosis for welders entering protection mode.

Broad fault entry

This page has a specific ZX7 / WS no-output role

This is a broad symptom entry for any welder with a protection light. Use the ZX7 / WS route when the machine is a ZX7 or WS inverter family.

Related ZX7 / WS no-output pages

ZX7 no-output content is separated by scope: broad protection symptom, generic inverter no-output, ZX7-250 specific symptom, no-OCV subtopic and the structured ZX7 / WS diagnostic route.

ZX7 / WS structured diagnosticMain route for protection light on, no output, feedback, thermal and drive-enable checks. Protection light broad faultGeneric symptom entry for any welder protection lamp. Inverter powers on but no outputBroad inverter no-output page. ZX7-250 fault light + no outputZX7-250 specific symptom page. ZX7 no open-circuit voltageNo-OCV subtopic. ZX7 / WS feedback protection pathCircuit path for feedback, protection and drive enable.

Symptom definition

Protection light on is a symptom-first page. It starts from what the user sees, then separates external problems from board-level causes. The same symptom can be caused by auxiliary supply failure, PWM shutdown, driver failure, power-stage damage, secondary rectifier damage or feedback errors.

Diagnostic flow

Confirm external condition

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Check input and DC bus

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Check auxiliary supply rails

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Check PWM controller status

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Check shutdown / protection path

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Check driver waveform

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Check power stage

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Check secondary output path

First checks

Confirm input voltage and machine mode.
Inspect output cables, clamp, torch and connectors.
Look for protection light, fan behavior and relay clicking.
Inspect for burnt resistors, cracked capacitors, loose connectors or damaged traces.
Use a current-limited setup for board testing when possible.

Board-level causes

Missing or unstable auxiliary supply.
PWM IC powered but blocked by shutdown/protection.
Current feedback path abnormal.
Driver transformer or transistor stage faulty.
MOSFET/IGBT short or open.
Secondary rectifier, output inductor or shunt feedback problem.

Test-point mindset

A useful repair note records both the measured value and what it means. WelderData pages are structured to convert repair cases into test-point tables rather than raw image dumps.