Apple has posted a downloadable edition of Micromat’s TechTool Deluxe, which is normally available via disc to AppleCare customers.
Apple describes TechTool Deluxe as “a powerful diagnostic utility that allows you to test your computer’s critical system components, such as the processor, RAM (random-access memory), VRAM (video random-access memory), the hard disk, and more. TechTool Deluxe can also repair your computer’s disk structure and rebuild its directories as necessary.”
To use Apple’s download link, you’ll need your Mac’s serial number, which is associated with your AppleCare account.