Fault

IGBT / MOSFET keeps blowing

Repeated power-stage failure diagnosis: driver waveform, snubber, transformer and secondary rectifier.

Why repeated device failure happens

Repeated IGBT or MOSFET failure is usually a symptom, not the original cause. New power devices can fail immediately if the gate drive, snubber, transformer, secondary rectifier or PWM timing remains abnormal.

Safe diagnostic path

Remove / isolate damaged devices

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Check gate resistors and driver outputs

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Check snubber network

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Check transformer and secondary shorts

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Verify PWM timing with current limiting

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Install new devices

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Power up gradually

Checks

Check	Normal / Expected	Abnormal Meaning
Gate resistor	Correct value, not open	Uneven or missing drive
Driver waveform	Balanced and clean	Shoot-through or no switching
Snubber	No short/open	Voltage spikes destroy devices
Main transformer	No shorted winding	Excess current
Secondary rectifier	Not shorted	Primary overload
PWM timing	No overlap	Shoot-through risk

Repair principle

Do not install expensive power devices until the low-power drive waveform and downstream load condition are verified.

ZX7-250 lesson connection

Lesson-based IGBT replacement warning: verify driver chain before full-power testing.

The ZX7-250 lesson strengthens this fault page because it shows the correct order after a power tube short: use a lamp limiter, isolate the shorted H7B/power tube, verify that the control side still responds, then inspect the driver chain before installing a new device.

Power tube short found

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Do not replace and fully power immediately

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Check control rails

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Check driver output and gate path

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Only then install and retest