Fault
UC3846 no output
UC3846 no-output, shutdown and feedback diagnosis for inverter welders.
Symptom definition
UC3846 no output 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.