Load Short
Load short protection activates when the output current exceeds 110-120% of rated capacity due to a short circuit or excessive load impedance in the connected equipment. The control IC immediately shuts down the main switching to prevent transformer saturation and component damage.
Error Code
F906
Severity
Fault
Equipment
Power Supply
Manufacturer
ABB
Power supply shuts down within 50-100 milliseconds of power-on with no output voltage
Current limiting LED indicator shows solid red or fast blinking pattern
Output voltage measures 0VDC across all rails during attempted startup
Input current spikes to 2-3 times normal for brief moment then drops to near zero
Audible high-pitched whining from main transformer during brief on-time
Secondary side fuses blow immediately upon power application if not electronically protected
Shorted output rectifier diodes (Schottky or fast recovery) with resistance below 0.1 ohms
Output filter capacitors with internal short showing resistance below 1 ohm
Damaged load equipment creating short circuit path with impedance below 0.5 ohms
Defective current sense resistor (typically 0.01-0.1 ohm) creating false overcurrent signal
Failed PWM control IC with stuck-on output transistors causing continuous conduction
Shorted secondary windings in main transformer due to insulation breakdown or manufacturing defect
Follow LOTO procedures and disconnect all output loads before troubleshooting power supply
Measure output rectifier diodes with multimeter diode test - replace if forward resistance <0.1 ohms
Test output filter capacitors with insulation tester at 500VDC - replace if leakage >1mA
Isolate load equipment and measure input impedance - should be >10 ohms for most industrial loads
Replace current sense resistor if value has drifted more than 5% or shows signs of thermal damage
Test PWM control IC by measuring gate drive signals with oscilloscope - duty cycle should be <85%
Perform no-load startup test followed by gradual load application at 25% increments to verify proper current limiting at 110% of rated output
Safety First: Always isolate power and follow LOTO (Lockout/Tagout) procedures before working on electrical components. If unsure, contact a certified repair technician.
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