Turn off power and disconnect the regulator from the circuit if possible
Identify the regulator type and pinout from the datasheet
Inspect the regulator for visible damage, burn marks, or loose connections
Set the multimeter to DC voltage
Measure input voltage at the regulator input pin
Measure output voltage at the regulator output pin
Compare the output voltage to the rated value in the datasheet
Check the ground pin connection for continuity to circuit ground
Measure voltage drop between input and output pins
Verify the input voltage is above the regulator’s minimum required input
Verify the input voltage is below the regulator’s maximum rating
Apply a known load to the output and recheck the output voltage
Check for excessive output ripple with an oscilloscope if available
Test for short circuit between input, output, and ground pins with power off
Check temperature during operation for overheating
Replace the regulator if output voltage is incorrect or unstable