REPAIR AND DIAGNOSTIC REPORT
Equipment Model: Growatt SPF 5000ES Inverter

Repair Video: https://youtu.be/CqigOkkfp5c?si=QUe4XWQRv5-W7jVH

Status: Completed / Tested Pass

## 1. Initial Fault Symptoms & Diagnostics

The unit was brought in with a complaint of abnormal physical behavior and conflicting voltage readings.

• Audible Buzzing: A distinct buzzing sound was emanating from the main board, typical of high-frequency switching instability or a failing gate-drive circuit struggling to maintain proper PWM (Pulse Width Modulation).
• Display Miscalculation: The inverter’s LCD screen indicated an abnormally high AC output voltage.
• Physical Verification: A manual multimeter reading at the AC output terminals contradicted the display, showing a dangerously low voltage.
• Diagnostic Conclusion: The microcontroller was receiving incorrect feedback due to a catastrophic failure in the inverter stage’s gate drive isolation and regulation circuitry, causing the control loop to misfire.

## 2. Component Isolation & Findings

Upon stripping down the inverter and testing the control and drive sections of the H-bridge inverter board, multiple cascading component failures were identified:

• Optocouplers: The high-speed optocouplers responsible for isolating the low-voltage control logic from the high-voltage gate signals had degraded/shorted, preventing clean square-wave delivery to the switches.
• Gate Drive Resistors: The resistors inline with the IGBT gates were found to be either open-circuit or drastically out of specification (charred), caused by an over-current spike when the driving logic failed.
• Zener Diodes: The voltage-clamping Zener diodes, meant to protect the IGBT gates from voltage transients, were breached/shorted.
• IGBTs (Insulated Gate Bipolar Transistors): Due to the failure of the protective Zeners and the erratic drive signals from the optocouplers, the main inverter stage IGBTs suffered thermal/electrical breakdown.

## 3. Action Taken & Parts Replaced

The defective components were desoldered, pads cleaned, and high-quality, temperature-rated replacements were installed. Component Class Action Taken Role in Circuit Main IGBTs Replaced (Full Matching Set) Restores clean DC-to-AC inversion switching. High-Speed Optocouplers Replaced Restores clean signal isolation between MCU and high voltage. Zener Diodes Replaced Restores over-voltage clamping protection on the gates. Gate Drive Resistors Replaced Restores correct current-limiting to the IGBT gates.

Note on Repair: Standard practice for the Growatt SPF series dictates replacing the drive resistors and Zeners whenever the optocouplers or IGBTs fail, as they almost always take collateral damage during a fault event.

## 4. Post-Repair Testing & Calibration

1. Idling & Waveform Test: The unit was powered on via a current-limited DC bench supply. The buzzing noise has been completely eliminated.
2. Voltage Alignment: The AC output voltage was checked via the internal display and verified simultaneously with a True RMS fluke meter. Both now match perfectly at the standard rated output voltage (with 0% deviation).
3. Load Test: The inverter was subjected to a stepped load test to ensure the new IGBTs handle high-current switching under thermal stress without dropping frequency or voltage.
   Final Status: Ready for re-installation.