PC Hard Drives (hdd)

Inside a Hard Drive

laptop hddI bought a new 60 Gigabyte laptop hdd (2.5" hard drive) a couple of months ago to use as backup for all my files. Unfortunately last week this hdd failed. The hdd contained everything including all my music, videos, software and all my documents. It is under warranty and I could have got a replacement but that was no good to me as it was the information on the hdd not the hdd itself that I needed. (warranty became void once I open the unit)

I decided that I would attempt to repair it myself as I knew the heads and platters (disks) were ok and this unit had simply just died. There was no sound from the motor spinning up when power applied, totally lifeless.
The pcb (printed circuit board) contains surface mount components and various ics' (controller, motor drive, eeprom, etc), so a successful repair was going to be difficult without a circuit diagram, especially if an ic was faulty. I was hoping it was going to be something fairly simple which in the end proved to be the case.

hdd pcbAfter removing the pcb from the drive, my first test was to follow the 5 Volt supply line from the connection pins. (pins 3 and 4 on the pcb starting from the top as you look at the diagram on the left)

Although you can't see it on the diagram, there is a fusable resister across the power rail where the arrow is. Using an ohmmeter I discovered this was high in resistance and needed replacing. Because I didn't have a circuit diagram i didn't know the exact value of this resistor, but with it being fusable it would surely be something like 0.1 or 0.01 ohms. I replaced it with a standard quarter watt 0.1ohm carbon fusible resistor.

After visual checks on the pcb using a magnifying glass I decided to put it back together and see whether the problem was either just a blown fuse or whether the problem was 'more serious'. If the fusible resistor blew again i would know.

It powered up without any problem and after 2 hours reading and writing to the drive it continued to work ok.

laptop hddThis is actually the second drive i have repaired where the fusible resistor has blown. If you don't have a fusible resistor NO DOT use a wire link to short across. This works fine but is definitely NOT advisable because the fuse is there for a reason, if you have a short somewhere else, instead of blowing the fuse it will destroy the drive and possibly also your computer motherboard.

The two different drives (Hitachi travelstar, Fujitsu) were slightly different, one had one fusible resistor and the other had two. Also the fuse could be on the ground rail instead of the + supply rail.

hdd plattersThe image on the left is the HDA (hard drive assembly). This drive was a 40 Gigabyte drive and had two platters (disks) and four heads. (one head per side). It is not advisable to open the HDA and doing so would destroy the drive. A 'clean room' is needed so that no dust enters the HDA bearing in mind these spin at approx 5400rpm.

The heads had gone on this unit (not reading, permanently ticking and clunking). I removed the platters and put them in an identical drive just to remove the information from them. I bought the identical drive from ebay for £12 so was worth the money recovering my files. I don't have a clean room so I was lucky this worked. Although this drive still works, i couldn't trust it with my files simply because I had opened the HDA in an uncontrolled environment.

jon rayner 2006