Fixing a dead Seagate 80gb drive
In case this helps someone else:
A colleague was given a broken PC. They were told that the power supply had blown, and the owner decided to buy a whole new PC rather than bother to fix it. I was asked to to try to get it to go. I tried a different ATX power supply and after some false starts I got most of the PC going again. It had two internal drives; a 10GB IBM drive plus a Seagate 80gb (ST380023A Barracude V). One thing I did find was that even with a new ATX PSU, the PC would not turn on with just the power of the 80gb drive connected. There was something seriously wrong with the 80gb drive. Anyway, I returned the PC and said both the power supply and the 80gb drive were broken, so they'd at least have to get a new PSU. I kept the 80gb drive since it was 'junk'.
But I was quite curious about the 80gb drive. I measured across the power connector. Between +5V and GND was some resistance, but +12V to GND seemed like a short circuit. Fortunately I actually had a working Seagate ST380023A Barracude V drive in another machine, so I pulled it out to compare. Interestingly this drive was bought from the same shop during the same month (per the warranty sticker) and had the same firmware version, but the logic boards were actually slightly different. Anyway, on my working drive, I traced where the +12V line went and found a few things it connected to. One of these was a little black square with markings BUX C240 with two pins on it (which I think is a diode). Its down near where the Power supply connector comes in. By desoldering one end of this from the dead hard drive, I could see that the short circuit between +12V and GND was removed. I have a diode tester on my multimeter and I could see that the BUX C240 was shorted out. My working 80gb drive had a similarly placed black square which I could see was not shorted out. It had the markings BUF C242 I think. I then scrounged through my junk pile and found an old 630MB hard drive that was dead and desoldered a diode from it (well I think it was a diode - it was a black square with a line on one end and had two pins on it). I can't remember what the markings were. I soldered it in place of the BUX C240 on the dead drive making sure the line on the packaging was oriented the same way.
I then powered it on and suffice to say it now works perfectly. I have been told by more wise electronics experts that the diode may be a zener diode to provide over voltage protection and that my generic replacement might not protect it from over voltage ... but hey it works for now.
Update (Dec 2004)
I came across a Seagate 40gb drive in an online auction advertised as:
Was working one day then stopped during a storm - never to go again
Of course, I had to bid on it to see whether it had the same seized diode fault ... didn't I? Well, NZ$7.50 later I had said 40Gb drive. This time it was shorted out between +5V and GND. Between +12V and ground was fine. Poking around with my multimeter I soon found a diode that was shorted. I replaced the diode and the drive seems to work fine now. Too easy.
