APC Smart-UPS SRT 10000VA Inverter MOSFET Bridge Repair - Pharmaceutical, Baddi
Fault Analysis
The Problem
Complete inverter shutdown on mains failure with 3.2-second power loss to data center servers
Three parallel IRF3205 lower-leg MOSFETs hard shorted (DC bus short-circuit current 150+ amps)
UC3876 gate driver IC internal short-circuit due to voltage overshoot during mains-to-battery transition
Bootstrap bias capacitor failed (2.2µF/400V dropped to 0.8µF, ESR >5 ohms)
Snubber diode reverse recovery failure causing 78V overshoot spikes on MOSFET gates
Money Saved
Cost Savings Breakdown
What this customer saved by repairing instead of buying new
* Govt. taxes extra as applicable · Shipping charges extra as applicable on the repair quote.
This Repair's Journey
From Inquiry to Delivery
Completed in 48 hours
Inquiry Received
Equipment details logged, initial assessment scheduled
Diagnosis & Evaluation
Component-level fault analysis with detailed report
Repair Work
Expert component-level repair using OEM-grade parts
Testing & QC
Full-load testing under operating conditions, QA sign-off
Delivery & Warranty
Dispatched with test report and 6-month warranty
Inquiry Received
Equipment details logged, initial assessment scheduled
Diagnosis & Evaluation
Component-level fault analysis with detailed report
Repair Work
Expert component-level repair using OEM-grade parts
Testing & QC
Full-load testing under operating conditions, QA sign-off
Delivery & Warranty
Dispatched with test report and 6-month warranty
Technical Details
Our Repair Approach
Mains-Off Bench Diagnostics and Thermal Imaging
Powered unit on AC mains, confirmed rectifier/charger healthy, battery at 27.4V, triggered mains-failure simulation and observed zero inverter output with rapid relay clicks; infrared imaging showed 71°C hot spot on MOSFET heatsink assembly.
Oscilloscope Analysis and Gate Driver Inspection
Connected DSO to UC3876 gate driver outputs and observed corrupted PWM signals with DC offset; visual inspection under magnification revealed three IRF3205 MOSFETs with thermal stress marks and junction vaporization.
Component-Level Testing (MOSFETs, Gate Driver, Capacitors)
Curve tracer confirmed three parallel lower-leg MOSFETs shorted drain-to-source; IC parametric test showed UC3876 gate-source leakage >10 mA (failed); bootstrap capacitor capacitance dropped to 0.8µF with ESR >5 ohms.
Full Inverter MOSFET Bridge Replacement and Upgrade
Desoldered three IRF3205 MOSFETs and replaced with matched military-grade IRF3808 devices; replaced UC3876 gate driver IC with equivalent; installed 3.3µF/450V film capacitor (upgraded from 2.2µF/400V); installed zero-reverse-recovery Schottky snubber diode array (MBRS10150CT).
Solder Joint Reflow and Bias Voltage Recalibration
Performed controlled nitrogen atmosphere reflow of all inverter stage solder joints; recalibrated gate-source bias voltages to specification and verified gate drive timing on oscilloscope.
Full-Load Inverter Validation Testing (90 Minutes)
Executed 90-minute load test at 10 kVA rated output, confirmed <2% THD, zero overshoot on mains-to-battery switchover transient, and stable 230V±2% output across all four inverter phases under dynamic load steps.
Mission Accomplished
The Result
Unit restored and returned to customer within 42 hours (14 March 14:00 → 16 March 08:00). Customer saved ₹2,30,000 compared to OEM replacement, achieving 63% cost advantage while restoring pharmaceutical data center protection immediately and preventing regulatory audit complications.
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