Monday, August 1, 2011

TVS diode and the dead hard drive

I try to be as helpful as I can to anyone who needs help.  On this occasion, I was attempting to reimage a windows box and keep the basic documents, pictures, music, etc.  Everything seemed to be going really smooth.  I removed the malware pieces in order to navigate around without interruption.  Got all the data.  Got the fresh image back on.... no problems.  As I attempted to use the external hard drive (one I have used for many years and many times), something went wrong.  I plugged the power adapter into the external hard drive, it came on, and the nothing.  There are lights around this hard drive and when the lights went out, they wouldn't come back on.  The data that was just backed up was still on this hard drive.  Also, some of my data was on this hard drive.  Through some frantic online reading, I thought it could probably be the TVS diode. In it's full name, it's known as the transient voltage suppression diode.
The theory here is that the power coming into the device was over 12V.  When this happened, the TVS diode protects the other components on the hard drive by not letting anything past it.  One of the big reasons I came to this conclusions was because this bad hard drive was not making the normal bad had drive clicks.  If it had any power, it would power on and the platters would spin a bit before clicking.  There are ways of testing your TVS diode with a multimeter.  After identifying and removing the 12V TVS diode, this hard drive acted just fine.  I did remove the hard drive from it's external enclosure as well as make sure I had a good power supply after the TVS diode was removed.  Lastly, the TVS diode was cut from the board.  My  soldering iron wasn't getting the job done and I didn't want to damage anything.  I don't recommend cutting the TVS diode from the board.  The picture below is of the hard drive with the TVS diode removed.

For more information:
On TVS diodes: http://en.wikipedia.org/wiki/Transient_voltage_suppression_diode


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