I bought a cheap kit allowing me to use a 3.5 SATA hard drive with a laptop, by plugging it in with USB. It still requires external power supply so I used an adapter that came with this kit but I plugged it the wrong way - the molex cable has four wires - one yellow, two black and one red and they are labeled 1, 2, 3, 4.

The power supply exploded (the enclosure is fine but it sparked) when I plugged it in, probably because it was plugged in the wrong way. Could this kill my hard drive? There wasn't any smell coming from the hard drive but I'm not sure that it wasn't fried.

When I shake the power supply I hear a rattling sound (similar to what you hear when you shake a burned out light bulb) - is it a sign that the power supply exploded first and it saved my hard drive?

I found conflicting answers on the Internet: this link says that it shouldn't kill the hard drive but this said it should.

As I have no alternative power supply I can't check it right now (if there is another way to check if it's fine please post it).

  • 1
    Comments are not for extended discussion; this conversation has been moved to chat.
    – Journeyman Geek
    Feb 13, 2017 at 0:02
  • 3
    Can you provide a photo of this cable? There have been suggestions that it is not actually a molex cable.
    – DavidPostill
    Feb 13, 2017 at 14:42

6 Answers 6


Simply plugging the cable in backwards would not cause what you observed (although it isn't exactly good for the drive).

It should be noted that hard drive circuity has safety resistors on it to protect the logic board should there be an over-volt condition on the power connector. This is standard practice on most low-voltage electronic equipment. Even though the connectors are designed to not allow a backwards connection, the circuits themselves are still designed to handle the situation if someone somehow manages to do it. This is why the ground pins are in the center -- they're still ground no matter what way the connector goes in.

The hard drive is probably OK, but of course there are no guarantees here whatsover.

Here is what likely happened:

The SATA connector was either not crimped properly to the wires, or the components in the brick itself were not soldered correctly. Either way, that's a short circuit, and it's quite possible that not even a drop of power actually made it to the hard drive.

A standard PC AMP (Molex) power connector uses 18AWG wires, which can carry up to 10A of current each. SATA power connectors use 28AWG wires, which can carry only 1.5A of current each. Because hard drives can pull up to 6A of power on the 5V rail (which exceeds the current-carrying capacity of any single 28-gauge wire), each 18 gauge wire on the Molex connector is crimped to three of the 28 gauge wires on the SATA connector so that the current load is spread out over them. In electrical work, this is known as ganging.

Here is a pin diagram of a SATA conector. Note the matching Molex wire color in the right-hand column: (Also note that Molex connectors do not provide a 3V line).

enter image description here

Here is a picture of an un-crimped SATA power connector:

enter image description here

As you can see, the 28-gauge pins are tiny, and they MUST be lined up perfectly. If you've ever crimped an RJ-45 connector to an Ethernet cable, you probably understand how easy it is to accidentally crimp two wires down to the same pin if you don't line them up properly when you push the connector on.

This isn't a big deal with Ethernet, as even with PoE, you're only talking about 500mA of power there. But with SATA, it's literally 10 times that. Accidentally crimping a hot wire to ground creates a short circuit which is a very real fire hazard at those current loads.

I drew up this ugly diagram to show what would happen if the SATA crimp were crooked by just 1 pin.

enter image description here

All that power flows straight back to the brick over one ground wire with no resistance. Pop, sizzle, and fry. It would take a very well-designed, high quality power brick to handle that error safely. This is why you should never trust your electronic equipment with no-name Chinese garbage power supplies. This goes for PC's, phone chargers, and the like.

An improperly designed/built power supply can ruin your electronics at best, and start a fire at worst.

  • 8
    This answer hasn't gotten the love it deserves. It clearly explains what might have happened. and even has beautifully ugly freehand arrows. Though, its worth remembering most gear comes with some flavour of chinese power supply, with various levels of no-name or fakenameness, and garbagivity.
    – Journeyman Geek
    Feb 11, 2017 at 4:28
  • 1
    I agree that it's a decent answer, but IMHO it's too generalised and uses improper terms ('brick' is 'PSU', for example).
    – AStopher
    Feb 11, 2017 at 10:13
  • As for Ethernet connectors, it's been a while since I had to, but the ones I've used all seem to have plastic separators between every pin – self-aligning.
    – user1686
    Feb 13, 2017 at 13:01
  • In my case, the cable was inserted "diagonally" to achieve the result.
    – Tomachi
    May 7, 2021 at 13:20

There's no real way to tell if the hard drive's fine but this shouldn't happen.

Molex cables are keyed - though I suppose if it was truly dodgy the end connecting to the external power supply might be odd. Even then, typically what goes into the device is 'pure' DC.

As for power supplies, you might have a fuse or a blown out component like a voltage regulator but this is before power goes into the circuit board that adjusts the voltages for the hard drive.

So, no promises. From your description, the PSU is probably toast, and hacking it open to see if its a fuse (if there's one) or another component is a diagnostic step you should try. If nothing else, its not particularly trustworthy.

As for the drive, I'd do a visual inspection, sudden death of its enclosure may cause data loss and you MIGHT have burnt something out by doing the impossible and plugging things in the wrong way. There's no way to check short of trying it in a known good enclosure or system.

  • 8
    One thing I discovered, to my chagrin, is that the PSU end of modular power supplies is not standardized. Sad! Feb 10, 2017 at 16:08
  • 2
    @Spehro That might be on purpose. I doubt it would be a problem; but you could run into issues if people started mixing and matching between PSU's. I doubt the rating of cable coming out of PSUs varies a ton; but it could be dangerous if one manufacturer chose to cut it close knowing they had low power draw and then someone uses those in a higher power PSU and starts a fire.
    – JMac
    Feb 10, 2017 at 16:52
  • 57
    "Hacking it open [...] is a diagnostic step you should try." PSUs and transformers have capacitors which have it will kill you power even when unplugged and off for hours/days. The OP might become "poorly from too much electric"
    – Yorik
    Feb 10, 2017 at 21:09
  • 5
    PSUs are supposed to have discharge resistors on the capacitors to render them safe after input power is disconnected. I have had a shock when one failed though.
    – plugwash
    Feb 11, 2017 at 0:44
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    @JMac: Cables from one PSU will fit into a different PSU. Everything looks fine, but it will fry whatever components you plug in to it. It's happened to me. Feb 11, 2017 at 7:54

In these situations it is more likely to kill the hard drive than it is to kill the power supply.

However there is no way for us to know and the only way for you to find out for sure is to test it with another supply.

Note that it is generally quite hard to plug a Molex in the wrong way round without significant force. It's potentially possible you had a faulty power supply and plugged it in the right way round.


Sometimes the damage is done just until where the short-circuit occurred or the magic smoke was release.

So it was power adapter -> enclosure -> SATA HDD.

If you inverted the cable, it means that where it was expected +5 V, you injected +12 V. Yes, it's more than enough to fry some chips, since they have strict limits, and +12V should have gone to the HDD motor.

If the enclosure didn't had any chips or protection, i.e., the 12V didn't make something blow earlier (inside the enclosure), it might have fried some chips from our drive.

But it doesn't mean that everything is lost. I mean, your drive won't work right know.

But if there was sensitive data you want to recover from it, you can always try to exchange the controller board from it from another one, of the same manufacturer, same model, etc. Because the chips control many things, but the plates inside the HDD are probably intact, you might have lucky recovering some (or all) data from the disk.

You know that Murphy plays some rule here: if you were trying to destroy your drive so that nobody would recover anything from it, just plugging an inverted cable isn't enough to prevent that. OTOH, in the exact moment you want to recover information, Murphy comes and makes all information irrecoverable even if you replace the controller board.

  • 2
    Have you ever successfully replaced a circuit board? I'm pretty sure the control board keeps track of where data is written. See article: research.ibm.com/research/gmr/basics.html "After consulting the table of stored data locations in the drive's electronics, the actuator moves the head over the track where the chosen data is located." By minimum the circuit board will keep track of where bad sectors are. Feb 11, 2017 at 4:57
  • Yes, I have... Last time was about 8 years ago. Same model, capacity, etc. Think I could recover all I wanted (no, at the time I didn't try to recover the whole disk, just 40% of its size was the data I was after). Feb 13, 2017 at 12:37

This happened to me too! I bought a cheap Chinese ATA to USB device. The device did work, but it was designed with the ATA connector upside-down, so that when the button and indicator lights on the device were facing upwards, the hard drive was label-side down with the delicate circuits exposed, so I preferred to instead keep the hard drive upright and the device upside-down. At one point while using it, I forgot to insert the molex power connector into the device likewise upside-down, and although the connector is notched to theoretically prevent misconnection, the cheap plastic had enough give that it quite easily went into the socket.

There was a loud bang. A wisp of smoke blew out of the hard drive, and there was a burning smell. Both the ATA to USB adapter and the hard drive were dead.

The only saving grace is that the USB cable wasn't plugged into my laptop at the time.


Sure it killed the drive.

I've been in your situation, the first day on a new job.

I was able to escape the situation telling my boss "See, there is no way I plugged it wrong way, because the form wouldn't allow me to". I was confident that it won't fit in the wrong way, so I didn't check. It was a cheap chinese product, so it indeed fit the wrong way.

Then, the disk was unable to work. You could hear a "tic tic tic" sound, like a clock but faster. The only way to try to recover the disk, is to change the controller for a one working in another exact same disk. Of course, this only if you have luck and only the controller died. Other way, you have to send the disk to a professional data recoverer, which would cost you a lot.

  • That's what my guess was. It was some extremely cheap Chinese made adapter that has no quality control.
    – DrZoo
    Feb 10, 2017 at 18:48
  • 1
    This answer is based in assumption and personal experience, and not fact. From what the OP described I'd say that the PSU blew its fuse and probably fried the adapter, but the drive might just be fine.
    – AStopher
    Feb 11, 2017 at 10:14

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