Using Apple Hardware Test

To use AHT, you must boot from the AHT CD using the same procedure used for starting up from any CD. That is, insert the AHT CD into the optical drive on the system that you need to check, choose Restart from the Apple menu (Mac OS X) or from the Special menu (Mac OS 9), then press the C key until the Mac displays a small “loading” icon.

It takes about a minute or so before the Apple Hardware Test window appears. Notice the three tabs: Apple, Hardware Tests, and Hardware Profile. The Apple tab reveals information about AHT, such as the version number. By default, the Hardware Tests tab is active.

The Hardware Tests tab provides the following buttons:

• Quick Test conducts an abbreviated hardware test.

• Extended Test conducts a thorough hardware test.

• Shut Down quits AHT, ejects the AHT CD, and turns off the Mac.

• Restart quits AHT, ejects the AHT CD, and restarts the Mac.

Quick Test

A Quick Test is a brief, basic test of the system hardware. It takes just a few minutes to run. As AHT performs its series of tests, it explains what it is doing and what it has found in the Test Results portion of the window. You can click Stop Test at any time if you don't want to continue.

Extended Test

An Extended Test is a more thorough check of the system hardware than the Quick Test, and as such it takes more time to complete. As with the Quick Test, you can check the progress in the Test Results portion of the window and can stop the test whenever you want. Unless you are really pressed for time, you should almost always run the Extended Test instead of the Quick Test.

Looping Tests

AHT provides an option for looping either the Quick or Extended test. Using looping tests is one way to identify intermittent failures or heat-related problems and to confirm that a repair has been done properly. To make use of the AHT looping option, you must do the following:

1.	Start up your system from the Apple Hardware Test CD.
2.	After AHT has launched, press Control-L. You should see “Looping ON” appear at the bottom right of the AHT window.
3.	Click one of the two test buttons. A time notation of when the looping started appears. A running count of test loops appears as well.
4.	When you want to conclude the looping of AHT, click Stop Test. You see the number of test loops that have been completed.

Error Codes

The tests that AHT performs are all pass/fail. If a component checks out fine, it passes, and AHT moves on to the next component. If it fails, further tests are halted, and Apple Hardware Test produces an error code to let you know what has failed and the appropriate action to take. The error code appears in the Test Results portion of the AHT window.

The error code consists of three parts:

• The abbreviated name of the hardware test (in this case, “cpu_”)

• The function ID (in this case, “26”)

• The error number (in this case, “12345”)

Hardware Profile

Click the Hardware Profile tab to view detailed information about the hardware installed in the Mac being tested.

The information displayed in the Hardware Profile tab depends on the Mac model. It is similar to some of the information you receive from System Profiler (discussed previously), which can run only after a successful startup. Since AHT doesn't rely on the Mac OS, you can use its Hardware Profile tab to compile detailed specifications even when a Mac refuses to open the Finder.

The Logic Board section of the Hardware Profile tab identifies exactly what generation and model of computer you are working with. Since there can be numerous models within a product line, this is very useful information when you begin the troubleshooting process. Likewise, the Memory section details the installed memory module specifications. This area indicates whether a specific memory module is defective or outside of the required specification for the computer.

AHT Issues

The following are issues with AHT 1.2. For the latest information on this and other diagnostics, consult the Service Diagnostics Matrix.

• You cannot use Apple Hardware Test when a mouse is connected directly to the USB port on a PowerBook. Connect the mouse to a USB keyboard if available, or use the trackpad instead.

• It may take significantly longer than indicated on the Apple Hardware Test screen to run the Extended Test on a PowerBook with more than 512 MB of RAM installed; durations between 18 and 20 minutes have been observed.

• PowerBooks can use memory modules (DIMMs) that are detected as partly bad during startup diagnostics. AHT reports them in the Hardware Tests tab.

• While testing the video RAM, the screen may appear blank for an extended period, depending on how much video RAM is installed. This is normal.

• Since AHT does not notify you before the battery runs low, make sure the AC adapter is connected when testing notebooks.

• If AHT stops responding and you can't shut down or restart, press the power button until the computer shuts down. If that doesn't work, unplug the computer or remove its battery.

• Currently Apple Hardware Test does not test the following:

  • Keyboard

  • Inverter board

  • Trackpad

  • Power supply card

  • Modem EMI filter card (cable)

  • PCMCIA card cage

  • Fan

  • Wireless antenna

  • Microphone

To test these components, see the Troubleshooting section in the service manual.

Apple Hardware Test Exercise 1

Referring to Knowledge Base documents 25165, “Apple Hardware Test: Support FAQ,” 58624, “Apple Hardware Test: Technical FAQ,” and 31195, “Apple Hardware Test: Tests and Error Codes,” as well as the Service Diagnostics Matrix and accompanying Read Me files on the companion CD, answer the following questions.

1:	What families of products are compatible with Apple Hardware Test?
2:	Which of the following items should not be connected to a Power Mac G4 system while using AHT? (Choose all that apply.) SmartMedia reader USB floppy disk drive Apple Keyboard External FireWire drive
3:	How do you use Apple Hardware Test disc?
4:	What is the difference between the Quick Test and the Extended Test?
5:	Which of the following hardware components does Apple Hardware Test check? (Choose all that apply.) AirPort Card Keyboard Inverter board Display module Memory Video
6:	What does an error code of “mem_/X/X” signify?
7:	What keyboard command toggles looping mode on and off?
8:	You are using AHT to check an iMac (17-inch 1GHz) and get a test error code of “2GMC/a/b/xxxx.” What is the first step Apple recommends you take?

Apple Hardware Test Exercise 1 Answer Key

A1:	iBook, iMac/eMac, PowerBook, Power Mac G4/G5, Xserve, and Mac mini
A2:	a, b, d
A3:	Restart the computer with the AHT disc in the drive and hold down the C key until the “loading” icon appears. When the Apple Hardware Test main screen appears, follow the onscreen instructions and recommendations.
A4:	Quick Test is an abbreviated test of the computer's major components. You should use this when you don't have time to run the extended tests; the test takes only a few minutes to complete. Extended Test is more thorough and is recommended for obtaining a complete evaluation of the computer's hardware. The test usually takes about 4 to 8 minutes to complete, but could be longer. The length of the test mainly depends on the amount of RAM installed in the computer.
A5:	a, e, f
A6:	It signifies that memory should be replaced.
A7:	Control-L
A8:	Make sure that there is no Ethernet cable connected.

Apple Hardware Test Exercise 2

If you have the Apple Hardware Test CD and a supported computer system, perform the following steps:

1.	Start up the computer from the Apple Hardware Test CD.
2.	Run a Quick Test on the computer.
3.	Run an Extended Test on the computer.
4.	Enable test looping, and run at least three loops of a Quick Test.
5.	Access the Hardware Profile tab and read the information.