Diagnostic tool
IGBT Replacement Precheck Tool
Generate a WelderData pre-power checklist before installing and validating new IGBTs, MOSFETs or H7B-style power devices in a failed inverter welder.
Check each item before replacement
Precheck report will appear here
Tick the items that have been completed. The tool will flag missing precheck and staged power-up validation steps that can destroy replacement devices or hide a no-output condition.
Why this check matters
A failed IGBT or MOSFET is often the visible result, not the complete root cause. In WelderData power-stage records, repeated device failure usually requires checking the gate-drive branch, primary driver network, output rectifier path, control-power rails and staged power-up condition before a new device is installed.
The expanded checks include the 3846-style PWM output path, the primary-side driver device, the 102 capacitor and the 22Ω resistor path. These parts are upstream of the four isolated gate-drive outputs. If they are damaged or shifted, a replacement tube can fail even when the new tube and the secondary branch parts are good.
A jumping or unstable meter indication at the transformer-primary drive point can be useful evidence. It does not provide a calibrated drive voltage, but it helps separate a completely dead signal board from a board that is producing switching activity.
ZX7 series calibration and no-OCV reminders
For ZX7 series machines, a replacement-device precheck should not ignore current-feedback calibration and open-circuit voltage evidence. If the panel display appears wrong, use the WelderData current display vs shunt tool and control-board calibration reference before treating the power stage as repaired. If the machine has no open-circuit voltage after driver repair, separate display error, 36V supply, control-board OCV generation and 20040 output rectifier checks.
Dedicated driver IC protection checks
Some welder power boards use protected optically isolated IGBT drivers rather than a transformer-only drive stage. In that architecture, the replacement checklist must include positive gate bias, negative turn-off bias, UVLO, DESAT / VCE detection and fault-feedback reset. If a driver is intentionally holding the output low because a protection condition is present, replacing the IGBT will not fix the board.
How to use this checklist as a repair record
The checkbox result is only the fast decision layer. For a high-value repair record, copy the result and add the actual readings below it.
| Record field | Example entry | Why it matters |
|---|---|---|
| Failed device evidence | H7B / IGBT shorted C-E or D-S after discharge | Confirms that the visible power device is truly failed |
| Branch comparison | Branch C differs from A/B/D in diode mode | Prevents installing a new device into a damaged driver branch |
| Control rails | +15V, -15V, +5V present and stable | Separates missing control power from gate-drive output faults |
| Driver command | Pulse / jumping indication present at primary path | Shows that the driver is not being treated like a stable DC rail |
| Limiter result | Bright lamp cleared after failed branch isolation | Supports staged power-up instead of direct mains stress |
| Validation | DC bus, no-load output and external current meter / shunt recorded | Separates panel display behavior from real output recovery |
Use with these WelderData workflows
IGBT-ZX7-400 extra record fields
For IGBT-ZX7-400 style machines, add these notes to the copied checklist result when the failure involves repeated IGBT damage, lamp-limiter short evidence or weak output after repair.
| Extra field | Example note |
|---|---|
| Varistor / surge evidence | No cracked or shorted input surge absorber; line-side trip cleared. |
| Gate branch symmetry | All gate resistors, clamp parts and fast diodes compared branch-to-branch. |
| Secondary rectifier evidence | Output fast diode module checked before new IGBT installation. |
| Staged restart evidence | Lamp limiter, bus voltage, OCV and light-load welding result recorded before full-current test. |
Related pages
Chui Shui EP extra precheck record
For Chui Shui EP-style machines after IGBT failure, add these fields to the normal precheck record before full-power restart.
| Record field | Expected evidence |
|---|---|
| Trigger-board offline test | CN1 supply, CN2 enable/feedback state and CN7/CN8 gate-output evidence recorded. |
| Gate resistor and clamp network | R36–R39, R40–R43 and ZD1–ZD8 checked by branch. |
| Gate lead contact | Both IGBT trigger-signal lead groups confirmed tight and correctly routed. |
| HF absorption capacitors | Offline check completed before reconnecting HF power. |
| Staged restart | Low-voltage current-limited test or capacitor-energy waveform test completed before full load. |
Chui Shui EP calibration and staged-test addendum
When the failed welder is a Chui Shui EP-style machine, add the following records to the copied precheck report. These fields connect the normal IGBT precheck to the EP trigger-board and low-voltage test workflow.
| Addendum field | Record before full-power restart |
|---|---|
| VR1–VR7 state | Whether any trimmer was adjusted, original position if known, measured effect and final setting reason. |
| Model timing | 200EP about 45µs, 350EP about 50–55µs, 500EP about 55–60µs, plus actual measured period. |
| 30V current-limited result | Injection point, current limit, observed current and whether the test was stopped. |
| Capacitor-energy pulse result | Stored energy condition, waveform evidence and branch symmetry. |
| Final validation path | Resistor-load validation before welding load; HF reconnected only after the inverter path is stable. |
M57962AL / dedicated driver module addendum
For welders using dedicated IGBT driver modules, add these records before fitting replacement power devices.
| Record item | Evidence needed | Why it matters |
|---|---|---|
| Driver supply | Positive and negative gate-drive rail under safe test conditions | No valid supply means no valid gate decision. |
| Fault output | Fault state before firing, after firing and after reset | A protection latch may block output intentionally. |
| Short-circuit path | Load-side short, secondary diode and snubber evidence | The driver may be reacting correctly to a real power-stage fault. |
| Gate network | Gate resistor, clamp zener, G-E discharge and gate-lead contact | These parts can destroy a new IGBT even if the driver module is good. |
| Staged restart | Lamp limiter, low-voltage test or other controlled startup record | Full-bus testing without protection evidence risks another failure. |