Using the BoardView in conjunction with the Official HP 4540s Service Manual is the "pro way" to troubleshoot these specific issues:
Stop guessing. Stop reballing. Start probing with precision. Get the better boardview, and watch your repair success rate soar. hp probook 4540s boardview better
Standby IC (PWM controller) pins, feedback loops, and enabling signals. 3.3V / 5.0V Using the BoardView in conjunction with the Official