Faulty Hard Disk - Should I buy one? I might be lucky?

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Every so often, new sellers pop up deciding to sell faulty laptop hard disks. Often these people have a computer business and have diagnoised bad disks, which they throw in the ebay scrap box; to be sold off either as a job lot or individually at the end of the year. Possibly the money goes towards a champaign bottle… who knows? Often a 20Gig disk will be sold for around £2.00 with an additional postage of around £3.00 to £5.00.

Where is the profit in selling faulty disks and is it worth buying a faulty disk? Clearly if the seller is charging £5.00 for 1st class standard UK Mail there is a huge profit margin here, as laptop hard disks are incredibly light and small; should not cost more than £2.00 including packaging.

Even so, Is it worth buying a faulty disk? And what could you expect to get?

Well...first of all a hard disk is an incredibly complex piece of electronic and mechanical engineering built to incredibly small tolerances and high precision. A hard disk is manufactured in a dust free controlled environment, because even a speck of dust can render a disk unusable.

A disk sector is about the same size as a dust particle these days. If you get a couple of dust particles floating around in there the chances are your disk will begin to fail, and the disk will  be constantly trying to read/write data and failing to.

So clearly, opening up the hard drive to fix it from the inside will not be a sensible idea, unless you happen to have a dust free facility in your bedroom with an industrial 3 micron air scrubber machine which costs around 2.3 million pounds.

So why do people sell faulty hard disks? Often its ignorance, they think that the average run-of-the-mill ebay customer will have just such a facility I described above. Often, the logic is 'even if I get a pound for it, and anyway I've declared that it's faulty, so I'm not doing anything wrong.'

As a buyer should you buy a faulty disk, or a job lot of faulty disks and what could you expect to find?

If the disk comes from a computer company of "average intelligence" IT Engineers, the chances are they have already run the basic tests on the hard disks. Disgnostic tests are quite accurate they read SMART attributes, and perform read/write tests. It's very easy to diagnoise mechanical failures, as opposed to soft errors such as sector corruptions which can be remapped. If a disk begins to indicate mechanical failure you can be certain it will all be down hill in terms of reliability.

Put it this way, it's very unlikely that you'll be able repair the disk using scandisk! or any sector remap utility.

It is more likely that the types of faults discovered will be Hardware based and will require you to open up the disk; these are the most common types of problems currently found on laptop hard disks:

1. Dead disk no power going in - Electronic problem, bad PCB.

2. No Platter Spin - Bad motor, or fault in motor drive electronics.

3. Actuator fault - Head arms unable to position correctly.

4. Loud screeching noise - Motor bearing worn out, motor fault

5. Loud whistling noise - Heads scraping the metal disk.

6. Drive is not detected in BIOS - faulty firmware modules, bad  PCB.

7. Water damage - metal disk no longer clean and heads dirty.

8. Corrupted Cache memory - Static damage, bad PCB.

If your hard disk has any of the above faults, and 9/10 it will, then the best place for it is the bin; after all would you really want to use such a disk to store your precious mp3 and business accounts, knowing that this disk has been opened up and likely to be unreliable?

But what if you bought a job lot of identical disks? Surely it's possible to get one drive with bad mechanical parts but a good PCB and another drive with good mechanical parts but bad PCB, then it's simply a matter of exchanging the PCB's to get one working drive.... I hear you thinking.

No! That doesn't work either, because each PCB has an eeprom chip that keeps something called a defect list. A defect list is a list of areas on the disk not to be used. Defects are mapped out for each disk and written on a chip at the factory. Since each defect list is different and unique, swapping the list by swapping the PCB will make the hard disk unstable, because the drive will think that a certain part of the disk is good to use when it wont be, i.e. the defect list will be wrong.

So what if you're bodge-it-Jim and you decide to open up the hard disk and swap the platters, or even the actuator arms and you're not worried about some little specks of dust, what are your chances of success?

Well first you'll need the right equipment; as well as stray dust, the metal disks are sensitive to stray magnetic fields. In the factory, they use industrial strength degaussers to de-magnetise all metal equipment. So I doubt your £1 rusty screwdriver set from a bargain basement shop will fit the requirements. If your screwdriver has a magnetic tip and it happens to touch the platter disk - forget it - you've just corrupted the control tracks that were written there at the factory. There is no way to recover them, even with the mickey mouse low level format (zero fill) utilities found on the internet.

What if your disk is getting seek errors, there is a possibility that the voice coil actuator is failing, you may decide to replace it from a spare identicle drive, what are your chances of success? Quite slim. Even if you change the actuator arms and head assembly, there is a possibility that the new heads will not align onto the same zone as the previous ones. This is because of variances in manufacturing process. Hard disks require high level of precision, and the slightest misalignment, even 1/10 of mm, will have a huge impact on the operation. Although in my experience when recovering data, I’ve had good success mainly because I swap the whole actuator assembly and use the correct torque on each screw. And yes! Even changing the torquage on the screws for the head assembly makes a difference.

So my advice is do not buy faulty disks unless you’re willing to spend a day running diagnostics, low level formats, and possibly open disk repair surgery. With a very slim chance of being rewarded with a reliable disk drive at the end of the day.

Sure if you’re recovering data from a broken drive then it’s worth it because I am assuming the data you recover is worth more than the price of the disk. This is about the only time I might buy a faulty disk.

If you must bid on a faulty disk then ask some questions first:

1. Where did this faulty disk come from?  If the answer is we are computer experts – forget it. Chances are you will need to open the disk to repair it.

2. Does this disk make any noises, screeching noise or whistling noise?  If yes then – forget it.

3. Is this disk repairable?  If the answer is we are running a successful computer repair company but we know nothing about hard disks, and there is no way for us to test if this disk works or not – forget it.

4. Make it clear with the seller, is this disk spares? or is it repairs? If it is spares only – forget it. If it is repairs, what level of repairs are we talking about; Will i need my rusty old screwdriver?



Although this is by no means certain, perhaps some good indications of when to buy would be:

1. If the seller has tested the drives, and can give you some sort of assurance that the drive might be repairable through software alone but the seller has no time to run lengthy scan & repair programs.

2. If the seller has performed a minimum quick test and can atleast tell you that the drive is not making any whistling noise, screeching noise, spins, and is recognised by the computers BIOS. Even so it's still a risk as there are so many other things that can fail on a hard disk.

3. If the seller has formatted parts of the drive and is able to successfully use them to install an Operating System.



If all you have to go on is:

Faulty hard disk.  x GB. Looks good from the outside. No returns.



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