You'll need to know the following categories for the exams, which are presented in multiple-choice style:
Macintosh Service Certification Exam 9L0-010
Embedded Battery Safety
ESD (Electrostatic Discharge) Precautions
New Product Troubleshooting and Take-Apart Tips
OS X 10.8 Mountain Lion Troubleshooting Exam 9L0-064
iCloud and Messages
Installation and Recovery
Peripherals and Printing
Security and Privacy
Troubleshooting Tools and Procedures
User Accounts and Permissions
The best way to prepare for and take the exams
While most of the exam focuses on diagnosing potential issues, Peachpit Press sells a good set of Apple Pro Training Series study guides. The core book sells for about $45 in print and $36 in eBook format. The guides include review sections and quizzes. You can also find courses lasting as long as several days at authorized training centers. The cost and depth of the courses vary from center to center.
Once the exam begins, you have 90 minutes to complete the multiple-choice questions. Stay calm, take your time, and remember that you can go back to answer questions you might have struggled with during the course of the test. The scoring is, of course, immediate; you can find details about Apple's exam scoring in this FAQ.
If you don't pass an exam the first time, you can immediately retake it if you're willing to pay the exam fee again (at least, this has historically been the case). Apple takes the higher score and discounts the failed score. If you know the question that made or broke your score, for example, then it makes sense to retake the test on the spot.
Going through Apple Certified Macintosh Technician training and exams is a rough, somewhat expensive process, but it also opens new doors. And if you love diving into Apple's hardware and doing that i a significant part of your living, the certification is indispensable. Find the study materials that work for you, read and reread everything carefully, get comfortable with every chunk of Apple hardware you can get your hands on, be as efficient as possible at diagnosing problems, and you're on your way.
And if you accidentally set more than two hard drives on fire over the course of your Mac tech career, then you've got me beat.
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