iMac Startup Power System: Power-button signal fault
Pattern to record: The normal button action produces no response despite confirmed standby power.
Use the correct Mac power design
Identify the iMac before tracing power: the 24-inch Apple-silicon iMac uses its dedicated external adapter, while many earlier models take mains power into the chassis. Record whether the display, fans or other functions show any startup activity. The desktop’s physical power button or its connection may fail to deliver a valid start request.
Power and data precautions
The external adapter or internal mains supply can contain hazardous voltage; display removal requires trained handling. Shorting unidentified board points is not a safe substitute for testing the button.
Model-specific checks
- Identify the external-adapter or internal-supply design, then distinguish startup activity from a built-in display or backlight fault.
- Check the exact model’s button assembly, connection and start-request signal using its service information.
Repair and startup verification
If the checks support this cause, repair the confirmed button or signal connection after supply faults have been excluded. Verification should cover cold start, built-in display, brightness, processor load, sleep and restart.
Reference: Apple support guidance; Apple support guidance.
For an assessment of your iMac, contact AEPC in Burswood or call 027 908 8880. Provide the model and the conditions that reproduce this problem. Workshop visits are by appointment.