Hi, earlier today I was stupid enough to accidentally connect my notebook's power supply (output: 19V) to my external hard drive (requires 12V). The result is that the hard drive won't start anymore. After reading about some similar problems, I found out that my mistake most likely blew up a TVS diode and that unsoldering it might help me get my data back (I realize this removes the protection and that it's not safe to use as a permanent fix)

How can I be certain that the TVS is the problem? And if so, is it safe to unsolder it yourself?
How do I identify these TVS diodes? I obviously don't want to make things worse by removing the wrong component.

The external hard drive is a LaCie 301285E in it's enclosure there's a Samsung HD501LJ
A picture of the HDD's PCB is attached.

The goal should be retrieving my data. Thanks in advance.

TVS Diodes are the ones that connect +5volt to -5v and +12V to -12volt. By looking at your pic i woudl start testing the big big black ones on the power connector. Diodes should only let current pass one way. Use your voltmeter on Ohm and test both directions of the black components.

Anode to Cathode - Some reading
Cathode to Anode - None

http://www.elexp.com/t_test.htm

Using your meter on ohm after removing the faulty diode you still need to test if there is no short. Clip your negate to a screw that hold the MB and test 5v on ohms- you should NEVER get 0hm(short) test 12v - the longer fingers will give you a different reading because these are used in hot swap devices.

Plug in at own risk.

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If I'm correct, I identified the one on the right to be the 12V one and the one on the left to be the 5V one.
The 12V one shorts in both directions.
And the 5V one strange enough gives an ohm reading in both directions 30 Ohms one way and 170 Ohms the other way.

Shall I try and remove the 12V TVS diode?

You can remove both for temporary reasons. Your meter might show ohms in both directions - but generally that means a faulty diode anyway as a diode should STOP current going one way.

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The problem is that the state of the PCB is unknown. If giving power again without precautions (no, I don't mean the TVS) the big M chip fries, then the s**t level rise to the ears...

What can I say ? Who dares wins but like we say "chi rompe paga e i cocci sono suoi" (if you break something you have to pay, but the splinters are yours )

Yes, but also measure the resistance of the "125F, 16V" component near the power connector.

The part is a "miniSMDC125F/16", 1.25Amp, PolySwitch, by Raychem Circuit Protection:
http://www1.futureelectronics.com/doc/R ... __16-2.pdf
http://www.anglia.com/raychem/datasheets/187_216.pdf

It should measure close to zero ohms. A PolySwitch is a resettable device, so it should have survived the overvoltage.

The "125F, 16V" component measures a near 0 ohms indeed.

I removed both diodes and was able to start the hdd and recover all my data.
Thank you all so much for helping me!

You did all the work and took all the risks.
Congratulations.

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I had the same problem and symptoms with exact the same hard drive, already a year ago or so.

This night, almost discarding the drive, I decided first to spend a few minutes searching the web. With good result. I also removed the 12 V diode, and now the disk is up and running again

Where to order which part for replacement? Or am i just too confident that I will never put the 19 V again in the 12 V power supply connector?

Excellent pictures and good description.

See my FAQ:
http://www.users.on.net/~fzabkar/HDD/TVS_diode_FAQ.html

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They dont just protect from accidental inputting of 19V lighning, power surges etc.

You can be sure of every environment so either replace them or don't ever trust the disk with anything important

Just take the components of a old drive.