How to fix a dead hard drive
By Charlie Demerjian in Las Vegas: Saturday 05 August 2006,
08:12
WHAT DO YOU you do when your HD crashes and you don't want to spend
thousands of dollars on a professional recovery service? You do it
yourself, and with any luck, it will work.
Scott Moulton of Forensic Strategy Services went through the
process of trying to pull things off a 'dead' HD, focusing mainly
on a few things that are not painfully obvious.
The first thing is that in his view, about 85% of the dead
drives are due to software, not hardware. This can be
fixed with a bunch of tools, mounting in a different OS, using a
LiveCD, or simply trying it in a different version of the OS
itself. There are tons of tools, ranging from really expensive to
free to help you here, try them all if you need to.
The other 15% is mechanical, and that is where the problems
come in. 10% tends to be the electronics on the bottom, 4% are the
heads or platters, and about 1% is the motor. Because the
PCB on the bottom of the drive is usually held on by a bunch of
screws and not soldered to anything, replacing it is an easy thing
to do. Physically swapping the electronics is something a beginner
should be able to accomplish.
The problem is that those electronics tend to change on a regular
basis, be it the PCB and components, or the firmware, and it does
so without any warning. Because the drive is a self-contained unit,
who cares what happens on the inside. If you are going to swap
PCBs, you need a drive date coded within two months of the dead
one, less if you want to be safe. Basically, if you want to do
electronics, time matters.
The heads and platters that make up most of the rest are much more
tricky. If you have ever opened up a HD, you have seen the heads on
an actuator arm, and the platters. If you have one platter, you are
in pretty good shape, you can take it out, put it in a different
drive, and still have a slim chance of it working. If you have
multiple platters, you can not take them out and have any realistic
chance of ever recovering your data.
This is because the tracks on the hard drive are placed on at the
factory, and you can't modify them. Instead of the old way of doing
things, stepper motors moved a head a certain measured distance,
the newer way is that the tracks are all encoded with their
location. The heads move a bit, and then read where they are. If
they need to keep going they do, if not, they start reading
data.
The platters are therefore hard
encoded with locations, and if you unscrew the spindles, there is
nothing holding the platters in alignment. If you free them, you
simply have no way of realigning them. Since a sector is written
across platters, any misalignment will kill all data on the
drive. This means if your motor goes, the last 1%,
and you have more than one head, game over. If there are multiple
platters, you simply leave them there, anything else is
fatal.
This leaves you with moving heads. Simply put, this is a problem
that is solvable, but takes very steady hands as long as the
platters themselves are undamaged. The way you check this is
opening the case and checking the platters for visible damage. If
there is nothing visible, check the little air filter, if there is
silver on it, once again, game over. If the platters are OK, time
to swap heads and pray.
Overall, fixing a hard drive comes down to software tools, and then
rarely hardware swaps. If it is hardware, then you are usually
looking at a board swap, and barring that, things get messy. In any
case it is doable to fix things yourself, but be prepared to break
a few drives. Experimentation on non-critical data is recommended,
try it and have fun. ยต