Pattern to record: The desktop remains dark, restarts or fails to complete startup on its normal external power connection.

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. iMac does not run from a MacBook-style rechargeable main battery; a clock or backup cell, where present, is a different component.

Power and data precautions

The external adapter or internal mains supply can contain hazardous voltage; display removal requires trained handling. Do not order a laptop battery pack or apply battery-reset instructions to this desktop.

Model-specific checks

1. Identify the external-adapter or internal-supply design, then distinguish startup activity from a built-in display or backlight fault.
2. Record the model and startup signs, check the actual power source and distinguish no display from no power.

Repair and startup verification

If the checks support this cause, base the repair on the failed supply, startup circuit or display path found during diagnosis. 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.