Hard Drive Repair - PCB

scott · 发表于 2006-12-3 04:40:35

There is a certain amount of agreement, between several of the data recovery service companies, that replacing the PCB, on newer hard disk drives, is a bad idea. In fact, swapping the PCB may actually damage the drive further. They make a good case, have cited examples, and some have gone to great lengths to document their information.

Hard drive customization. At first glance the thought of each and every hard disk drive manufactured being customized, just sounds impractical. Writing variable data to each and every drive? Well apparently they do. If one stops and considers how easy it is and the benefits to the manufacturer's, even the most lay-person will agree.

The variable information is located in some key locations. One such location is the disk itself. There are tracks written to the drive that the average user cannot access. These are known as maintenance tracks. Another location is the EPROM on the PCB. After the mechanical portion of the drive is married to a PCB, during the manufacturing process, the drives are connected to a machine. This machine executes testing, burn-in, writing data to the maintenance tracks and EPROM. Technically, each and every ESDI, [wiki]SCSI[/wiki], ATA and [wiki]SATA[/wiki] drive produced has been customized. The manufacturer's have always stored media defect information in the maintenance tracks. Defects are unique to each drive. So it's not a big stretch to further customize each one. The manufacturer's can reduce their failure rate by tuning the customized information for the thermal and mechanical characteristics of each drive. With the ability to tune each drive made, they can also increase capacity by stabilizing these factors during the manufacturing process.

So how does that affect swapping the PCB? If each drive can vary slightly in it's operating temperature and some of the mechanical properties can be adjusted to compensate. It's not too far from the realm of possibility to introduce a "matched" PCB to a Head Disk Assembly (HDA) that is so different, the PCB could actually do damage to the HDA. One data recovery shop reports there are models of drives on the market where swapping a "matched" PCB to a failed unit's HDA, destroys the swapped PCB.

Consider a serialization scenario. A PCB can be serialized to work with a particular HDA only. That's not too hard. Just write the serial number to the EPROM and the maintenance tracks. During the start-up sequence require the two serial numbers to match. If it doesn't match, it doesn't work.

The future of drive customization is on the horizon. Some reports suggest that the manufacturer's are leaning towards drive level security. The critical information written to the maintenance tracks and the ERPOM, in theory, would be encrypted. That certainly won't make things easier for the board swapper or the data recovery shops.

Is there a "line" where a PCB shouldn't be swapped? The introduction of highly customized information written to hard drives (believe it or not) occurred, to some degree, at the 5MB level (that's 5 megabytes!). With each new generation of disk drive thereafter the customization becomes more intense. In general, the larger the drive the less successful swapping the PCB becomes as a repair solution. The actual destruction factor seems to be limited to particular models at the 20GB level and above. However, I do not have sufficient information to identify them.

I can no longer, in good conscience, recommend swapping PCB's as a repair solution. Do so at your own risk. If you insist on doing so anyway, please use the following guidelines;

For the purpose of hard drive data recovery, the easiest way to get replacement parts and repair your hard drive is to buy another one just like it. Exactly like! Down to the revision!! Including the board!!! That said, the easiest way to repair an electronic problem is to replace the PCB on the drive. There are other electronic components in the drive. But, we'd have to void the warranty and they require special tools to replace. Simply swap the boards from an identical drive? Make sure it's the exact same board! Don't assume it's the same because the model number is the same, or close. Using the wrong board could start a fire!

Swap the boards and see if the symptoms change.

If the symptoms improve to the extent that the drive is recognized by the computer BIOS or SCSI HBA, image the drive now. If the symptoms don't improve, the problem is beyond any help we could provide here. You need professional assistance.

These guides should give you a general idea of what to look for;

ccjoker · 发表于 2007-6-28 14:34:02

[s:7][s:7] thanks

甜橙 · 发表于 2007-6-28 20:10:59

Western Digital (WD) uses a combination of model/part number and a DCM number on the drive cover as well as a part number on the PCB.

Matching a PCB is relatively straight forward. First you'll need to match the drive model/part number. The entire number needs to match including the information after the dash. In the case of the drive shown, we need to match WD1200BB-00DAA3. The DCM is related to the firmware writen to the drive. (Read the repair-[wiki]pcb[/wiki] page regarding the drive customization) I don't believe it will be possible to match the DCM number exactly. Getting as close as possible is recommended. If and/or when a breakdown of the DCM number becomes available, I'll edit this page with the information.

Second you'll need to match the PCB part number as shown in the next image. The base part number is obviously important. The dash level is equally important, they must match to stand a chance of a PCB swap working. Lastly as hard drives get larger the revision (in the case of the ex[wiki]amp[/wiki]le shown "D") becomes more critical.

Hard Drive Repair - wdPCB

The physical design of the model shown in this example uses a flat or non-molded cover. The older style WD drive uses a molded (rounded edge) cover that requires tape to complete the seal. On the older style drives, in most cases, one can simply match a PCB with the same part number. Even if the PCB is from a different model you can generally expect to get acceptable results.

Hard Drive Repair - wdPCB

As with any PCB swap, doing so is a temporary solution intended to permit the imaging of a hard drive. In some cases one may be able to extract data from a drive with a replacement PCB, however imaging is strongly recommended. These types of component swaps are not long-term permanent solutions to a drive failure.