Power Mac G4 Cube: Troubleshooting: Power-On Light Self Test

This article explains how to interpret the Power Mac G4 Cube computer's power-on light flash sequence at system startup.
This article has been archived and is no longer updated by Apple.
The ROM of the Power Mac G4 Cube computer contains a self test that runs whenever the computer is turned on after having been shut down. It does not run if the computer is only restarted. If a potential issue is detected during the test, you will not hear a startup sound; instead, you will see the power-on light flash two, three, or four times.

Note: In this case, a flash is considered to be 1/4 second or 250 ms or greater in length.

Caution: To remove or reinstall the core from the enclosure, to install or reinstall memory, to understand and follow the Electrostatic Discharge (ESD) procedures and the general set up of the cube, please refer to the following materials:


This article covers repair procedures for authorized service providers on selected Apple products, but we have published them in the Knowledge Base for the general public for educational purposes. At this time, there are a limited number of repairs that customers can perform. These are documented under the customer installable parts program at http://www.info.apple.com/installparts/.

If you have not been authorized to perform these procedures, please contact Apple (800-APL-CARE in the United States) or your local authorized service provider to schedule a repair.

If you do not hear a startup sound, the power-on light will flash as explained below:

Two Flashes: No memory is installed or detected.

If memory is installed, ensure it is seated properly, as follows:
1. Shut down the computer by holding down the power button (about 5 sec.) until it shuts off. Then disconnect the power cord from the computer.
2. Remove the computer core.
3. Rotate the core so you can see the memory.
4. Eject and reinsert the memory to ensure the memory is seated properly.
5. After reseating the memory, replace the core in the enclosure.
6. Plug in all the cables, and turn on the computer.
7. If the light still flashes, contact Apple Support for assistance.

If no memory is installed, install compatible memory, as follows:
1. Shut down the computer by holding down the power button (about 5 sec.) until it shuts off. Then remove the power cord from the computer.
2. Remove the computer core.
3. Rotate the core so you can see the memory slots.
4. Install compatible memory. Refer to the Power Mac G4 Cube owner's manual, which discusses the type of memory that is compatible with the computer. You can also refer to http://www.apple.com/guide/, and article 58776: "Power Mac G4 Cube: Memory Specifications".
5. After installing memory, replace the core in the enclosure.
6. Plug in all the cables, and turn on the computer.
7. If the light still flashes, contact Apple Support for assistance.

Three Flashes: Incompatible memory types are installed (for example both SDRAM and EDO installed).

Install compatible memory, as follows:
1. Shut down the computer by holding down the power button (about 5 sec.) until it shuts off. Then remove the power cord from the computer.
2. Remove the computer core.
3. Rotate the core so you can see the memory slots.
4. Install compatible memory. Refer to the Power Mac G4 Cube owner's manual which discusses the type of memory that is compatible with the computer. You can also refer to http://www.apple.com/guide/, and article 58776: "Power Mac G4 Cube: Memory Specifications".
5. After installing memory, replace the core in the enclosure.
6. Plug in all the cables, and turn on the computer.
7. If the light still flashes, contact Apple Support for assistance.

Four Flashes: No memory banks passed memory testing.

Either the memory or the memory slots need replacement, as follows:
1. Shut down the computer by holding down the power button (about 5 sec.) until it shuts off. Then remove the power cord from the computer.
2. Remove the computer core.
3. Rotate the core so you can see the memory.
4. Remove all the memory.
5. Check to make sure there are no bent pins in the memory slots.
6. If there are bent pins, contact Apple Support for assistance.
7. This step covers a repair procedure for Apple Authorized Service Providers. At this time, there are a limited number of repairs that a customer can perform and these are covered under the customer installable parts program http://www.info.apple.com/installparts/. If you have not been authorized to perform these procedures, please contact Apple (800-APL-CARE in the United States) or your local authorized service provider to schedule a repair.

If there are no bent pins, reset the logic board as follows:
a. Remove the video card and video riser card from the logic board.
b. Replace the video riser card back in its slot.
c. Locate the reset button (S1) on the logic board, shown in Figure 1.



Figure 1 Power Mac G4 Cube logic board

d. Wait 10 seconds, then press S1 once. Do NOT press the reset button a second time.

8. Reinstall memory, and replace the core in the enclosure.
9. Plug in all the cables, and turn on the computer.
10. If the light still flashes, replace the memory modules.
11. If the light still flashes, call Apple Support for further assistance

Published Date: Oct 7, 2016