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Split-Half Search

A split-half search is a technique for systematically isolating the source of an issue. You start by eliminating roughly half of the items you are checking, then trying to re-create the issue. You continue halving your search group until you find the source of the issue. A split-half search requires applying your knowledge of the product, its common issues, and the symptoms as you check one possible cause after another, in a logical order.

This part of the troubleshooting process can be the most difficult and the most time-consuming. That's why a logical and methodical plan is so important. We've found that the following order has been effective:

  1. User errors. Check for user errors in the course of gathering information, duplicating the issue, and trying quick fixes. But keep in mind the possibility of incorrectly set switches or preferences, incompatible equipment, and incorrect assumptions on the user's part; take nothing for granted.

  2. Software-related issues. Software that is unusable or that doesn't work with other software, viruses, extension conflicts, duplicate System folders, and other software issues can cause symptoms that may look like hardware issues. But replacing hardware won't solve these problems, and it wastes time and money, so always check for software issues before replacing any hardware. MacTest Pro system software tests can detect and repair many software issues of this type. Remember that you must check applications and the Mac OS.

  3. Software viruses. As you most likely know, a virus is a program that replicates itself and often modifies other programs. When a virus gets into system software, the computer may not start up, the system may stop responding, or the software may work incorrectly. (It may be helpful to define this for a customer who really isn't sure why a virus could be such a big issue.) Although Macintosh computers are less likely to become infected with viruses than computers running other operating systems, it is still possible to get a virus on a Mac. Email attachments and other files downloaded from the Internet are common sources of virus infection.

    To check for a virus, ask customers these questions:
    • Did you recently receive software from another user or a common source and add the software to your system?
    • Did you experience the issue before you obtained the software?
    • Did you share this file with others? Are they having similar issues?

    You can find up-to-date virus information on the Internet at a variety of locations. Third-party virus utilities such as McAfee Virex (www.networkassociates.com) can check systems and remove viruses from them. Virex is available as a free download to all .Mac subscribers.

    If you do detect a virus, make sure you find the original source file and delete it. Then reinstall all affected system and application software, and dispose of any unusable data files.

  4. Hardware issues. When you are convinced that user error, a virus, or other software has not caused the issue, hardware is what is left. Here are some tips:

    • Simplify the issue. Remove external devices and internal cards (except the video card, if needed for display) and test the main unit alone. If the issue remains, you have isolated it to the computer itself. If the issue disappears, reinstall the cards and peripherals one by one, until the symptoms reappear. When they do, you have found the culprit—or at least a clue.
    • If the system can be tested with AHT, do so. This can often save you considerable time when checking for hardware issues.
    • Find the “problem space.” Try to identify the functional area—sometimes called a problem space—that the issue affects. For instance, the general functional areas for a typical Mac could be considered software, logic and control, memory, video, input/output (I/O), and power.

If you can narrow down the issue to, for example, the video area, you can narrow your search to the parts that relate to video: the monitor, cables and connectors, video random-access memory (VRAM), video card (if present), and logic board.

  • Inspect components, especially mechanical parts and fuses. You may be able to see the cause (a blown fuse or a visibly defective chip), smell it (a burning smell is often a tip-off), or hear it (grinding noises are seldom a good sign).
  • Work from largest to smallest components of the system. Avoid the urge to go straight to the heart of the issue. Instead, methodically work your way down, testing along the way. Gradually narrow the focus of your search. For example, if you suspect there is an issue with a component of the System folder, you would want to first check the complete Mac OS by starting the system from a known-good CD with the same version of the Mac OS. Only when you know that the rest of the computer system is working correctly would you want to start investigating the components of the Mac OS.
  • When testing, test only one thing at a time. It is ultimately more efficient to methodically test one thing at a time and move on to the next than it is to try two or three things at once. This means reinstalling the original part if a replacement part does not correct the issue. Always work from the original system at each step.

If a test you perform does not reveal the source of the issue, restore the system to the condition it was in and move on to the next test. Make a note of what you just tried and what the result was.

If you have backups of the files you update or replace, you can return the system to its former state after each test.

Good Technique

  1. Disconnect external USB and FireWire devices.
  2. Check result.
  3. Reset PRAM.
  4. Check result.
  5. Start up from another System folder (such as a bootable CD).
  6. Check result.

Bad Technique

  1. Disconnect external USB and FireWire devices, reset PRAM, and start up from another System folder.
  2. Check result.

Troubleshooting Flowchart Exercise

  1. A customer tells you that his or her iMac has stopped working. The first thing to do is:
    1. Run Apple Service Diagnostic.
    2. Try quick fixes.
    3. Run MacTest Pro tests.
    4. Gather more information.
  2. The hard disk does not appear on the desktop of a PowerBook G4. You cannot resolve the situation over the phone, so the customer brings the system to you for repair. What items would be useful for repairing the issue? (Choose all that apply.)
    1. Replacement keyboard and mouse
    2. Apple Service Diagnostic
    3. System software CDs
    4. Replacement module for the hard disk
    5. Tools
  3. Which of the following is not an example of a split-half search process?
    1. Check for software issues before replacing any hardware.
    2. Remove external devices and internal cards, and test the computer by itself.
    3. If a module is easy to replace, swap it right away.
    4. Inspect components visually.
  4. A customer's Power Mac G4 running Mac OS X 10.2.6 does not turn on. What is the first step to take?
    1. Run Apple Service Diagnostic.
    2. Refer to Service Source.
    3. Check the power source and cable connections.
    4. Reset the PRAM.
  5. What is the first step to take when a computer with a CRT display starts up to a black screen?
    1. Run Apple Hardware Test.
    2. Adjust the brightness and contrast controls.
    3. Rebuild the desktop.
    4. Reset the PRAM.
  6. You cannot solve an issue after trying quick fixes, running diagnostics, and consulting the troubleshooting charts in Service Source. What is the next step to take?
    1. Call Apple.
    2. Look up the issue in the Knowledge Base.
    3. Check the cable connections.

Troubleshooting Flowchart Exercise Answer Key

  1. d
  2. b, c, d, e
  3. c
  4. c
  5. b
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