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Please note, this is a "why" question, not "how" or "how to fix" question.

So a friend of mine has recently fried 3 laptops in short succession. First was a 2014 Razer Blade, the other two the 2015 model. Razer RMAed the first one and replaced the motherboard, and had him return the second to Amazon. The support people don't know what the issue is.

So how did this happen?

He was charging his Huawei Watch from the USB port. The watch works fine, it charges correctly, there are no problems charging with it plugged into other computers or the wall charger. Furthermore, there were no issues charging other devices from the USB ports of any of the computers.

But in all three cases, he woke up to a computer that would not turn on.

So why would a charger/device that causes no other problems, charging from a port that has no other problems... fry three computers?

Notes:

  • The system was plugged into the AC at the time.

  • The system was asleep at the time.

  • All of the Blades ports are USB 3.0

  • One of those ports can be set to always provide power (even while off) for charging.

  • The watch was not plugged into that particular port.

  • Razer considered this normal usage and replaced the motherboard under the (expired) warranty.

  • After the third one, Razer did ask him to stop charging that device with it. But only because they can't think of what the problem could be.

I ask this question not because want to find a way to fix it (though that would be nice), but I am curious as to what could be the cause. I really doubt Razer will be forthcoming with that knowledge if they figure it out, which I am less than confident that they will.

I considered posting this on https://electronics.stackexchange.com/ since it may come down to a more in-depth understanding of the circuits involved.

So what could possibly cause this to happen? I can see how a short could be a problem, but that should be a problem for the watch too - and it would be an issue regardless of power source.

To clarify my actual question:

  • Assume that I already ruled out issues not directly related to the devices discussed above (because we have).
  • Assume that there is something in the design of the watch, it's charger, or the laptops, (or combination of those things) that is responsible for this problem.
  • Assume the watch doesn't cause problems for any other computers (it hasn't).

What kind of electronic problems could produce this? It's happening, so surely there is an explanation.

I'm not asking for troubleshooting help. This isn't a question of "how to fix".

  • I don't see how we could possible answer this question. Charging a USB device while plugged into a PC will not damage it. Something else is happened that actually caused the damage. – Ramhound Oct 28 '15 at 18:45
  • Under normal circumstances I would agree, however this happened three times, on three nearly identical but independent systems. But not on any others. – zeel Oct 28 '15 at 18:48
  • If the watch was functional I don't see how it could. I suppose it could be a defect in the watch's design, if that is the case, contact Huawei for assistance. If the laptops were always plugged into the same outlet, I would first blame the outlet or the wiring, before anything else though. – Ramhound Oct 28 '15 at 18:54
  • We considered that, but ruled it out. For one, the outlet and wiring are fairly new (not an old house). Furthermore, nothing else plugged into that outlet ever had an issue. And finally... the system(s) spent a significant amount of time plugged into that outlet without any problems. – zeel Oct 28 '15 at 19:10
  • While this is understandably frustrating, but given the watch is obviously causing the problem have you considered just... not charging it from the laptop? Incidentally, does the laptop still charge stuff after it's "died"? – qasdfdsaq Oct 28 '15 at 20:12
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Probably bad luck. USB is designed to survive quite a bit of maltreatment. In particular, the power circuits should be protected by electronically resettable fuses. Even a hard short circuit should not damage the USB port, let alone the whole computer.

  • Well, we don't really know what got killed - only that you have to replace the entire motherboard to replace it. Which is normal for most parts of a laptop. – zeel Oct 28 '15 at 18:33
  • While everything should be protected in an ideal world, a lot of cases they are not. And not to mention electrostatic discharge is often not protected against by fusing because they are not conducted along the power lines. – qasdfdsaq Oct 28 '15 at 20:14
  • @qasdfdsaq: Actually the USB standard requires overvoltage protection for all pins, and additionally overcurrent protection for power. Electrostatic discharge is an overvoltage problem. – MSalters Oct 28 '15 at 23:57
  • @MSalters: And we all know absolutely everyone adheres to all standards 100%. Just like the ATX standard requires a minimum of 16ms of holdup time yet 70% of "premium" power supplies fail to meet this minimum. – qasdfdsaq Oct 29 '15 at 11:27
  • @zeel With laptops, the motherboard basically is the entire computer. Even more so than with desktop systems. So the fact that on a laptop after a problem the motherboard needed to be repaired or replaced basically doesn't say anything. – a CVn Nov 2 '15 at 20:15
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USB has 5v power on one pin, and ground on the other. If the USB 3 supply was of high current, it could be tripping circuit breakers in the power supply of the laptop. These might be fuses rather than resettable relays or switches, in order to keep size and cost down. So they might replace a really cheap fuse and resell as a refurbished item.

Try charging the watch on a different laptop. Probably the cable or plug would have the short in it. I did have a pci to USB card go bad with the same result. Remove the card, system would boot. Plug in card, audible click, then no boot.

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