How can I wipe a broken hard disk drive before sending it back to the manufacturer for maintenance?
Do not return the drive if it contains customer or legally protected personal data.
For what it is worth, you may find that if you explain the situation to the support rep they will waive the return and let you destroy the dead drive.
HP have done this for me in the past.
Just tell them that you don't want to return the drive because of sensitive data, and you prefer to physically destroy it. The probable reason they want the dead drive is to make sure it really is dead and you aren't just trying to blag a free one. As long as they believe you they will probably let you keep it.
If they insist, then if your data is important and/or legally protected (most business data is), just take the hit on the cost of the drive.
For completeness, there's always demagnetizing. Look for degaussers. You can also get a bunch of magnets and hope that scrambles enough of your data.
NSA approved degaussing wands appear to run about $500 - $600.
There are some vague forum reports of buying very strong neodymium magnets and using those to degauss the drive by rubbing it on both sides:
I got the idea of using a permanent magnet to erase the drive but I read many postings of people who tried but failed using old speaker magnets. I then found a site called K&J Magnetics (http://www.kjmagnetics.com/) which sells super strong neodymium rare earth magnets.
I did some experiments on an extra working drive. The neodymium magnets fully erased a hard drive with less then 30 sec of rubbing in circles on both sides of the drives. They also worked great to erase 3-1/2" floppy disks and some flash memory cards.
Just be careful to read and heed the warnings about the magnets on K&J's site. The magnets are much stronger than you could imagine. Getting your finger caught between two magnets will cause a serious pinch. Also they are incredibly hard to get apart once they stuck together.
Looking through the magnet selection, one of the larger neodymium magnets will run you from $5-$20 so that's much more cost effective, if it works. However, according to their own blog, which performed an actual experiment on a live hard drive, this doesn't work at all! Per the comments, this might be because simple magnets don't offer the rapidly oscillating magnetic field that the commercial degaussers do.
So, pending any other experiments, I'd call the cheaper neodymium magnets busted; it's either the $500-$600 degaussing wand, or nothing.
Its very hard to destroy data on a hard drive securely if you can't write to it. You could try downloading Darik's boot and nuke from http://www.dban.org and see if its able to run at all on the drive. You could also check if the manufacturer has a wipe policy on disk arrivals (Seagate does).
If you're particularly paranoid, buy a new drive and stash the old one in a safe until the data is no longer a security problem.