iMac Troubleshooting Input/Output Issues
Troubleshooting USB-C and Thunderbolt issues
Identify issues
USB-C device isn’t recognized or isn’t powered when connected to the computer's USB-C ports.
Thunderbolt device or display isn’t recognized when connected to the computer's USB-C ports.
Try quick troubleshooting steps
Ensure that you aren't exceeding the specified maximum number of supported external USB-C devices, Thunderbolt devices, or displays for this model. Refer to Identify your iMac model, Identify the ports on your Mac, and Connect a display to your Mac.
Inspect all USB-C ports and enclosure openings on the computer for any signs of deformation, damage, or debris that may be blocking the connection.
If you find any debris in these ports, gently clean each connector using a small, nonmetallic, soft-bristled brush. Ensure that the brush is clean and dry. Gently brush out lint or debris. Twist the bristles to loosen and lift out debris. Brush debris away from the connector to avoid pushing debris into the connector. Use a microfiber cloth to wipe away the loosened debris.
Caution: Unplug all cables and turn off the computer first. Don't use aerosol sprays, solvents, abrasives, or cleaners containing hydrogen peroxide that might damage the finish. Don’t use any metal objects to clear debris or obstructions, as this can short the connector and cause damage. Avoid getting moisture in any openings, and don't spray liquid directly on the computer. Don't use compressed air.
Refer to steps and support resources in Troubleshooting Quick Checks.
Run manual and diagnostic tests
If the issue wasn’t resolved by following a support article or checking for potential causes, run these diagnostic and manual tests to help isolate the cause of the issue:
Connect a compatible mouse or keyboard to each USB-C port on the iMac to verify basic USB-C port functionality.
Ensure that the iMac recognizes the connection with both orientations of each USB-C connector by flipping it over and reconnecting it.
Connect an external Thunderbolt display to the iMac to verify USB-C port Thunderbolt functionality. Verify audio output if the external display has internal speakers. Verify that the external display shows a correct image and the external display’s speakers produce clear sound.
Open and inspect the computer
If your issue wasn’t resolved or isolated by following support articles or running diagnostics tests, refer to the computer's repair manual to open and inspect the computer. A damaged or out-of-place part may be causing one of the issues.
Note: This section requires ordering parts and tools. Replacing a part may not resolve the computer's issue. You can find other service options at support.apple.com/repair.
Replace the part
If the issue wasn’t resolved or isolated by following the previous steps, replace the following parts one at a time in the order shown. After you replace the first part, repeat the troubleshooting steps to determine whether replacing a part resolves the issue. If it still isn’t resolved, replace the next part.
Replace the affected USB-C I/O board.
Replace the adapter board (for iMac models with four Thunderbolt ports).
Replace the logic board.
Note: This section requires ordering parts and tools. Replacing a part may not resolve the computer's issue. You can find other service options at support.apple.com/repair.