YouTuber and electrical engineer BigClive has come across a USB hub that destroyed no fewer than three Mac motherboards – or so it’s claimed by one of his viewers who sent it to him. See the video after the jump, where Clive examines the hub.
Perhaps surprisingly, the hub isn’t faulty. By design it backfeeds five volts to the computer it’s attached to via the USB uplink cable. Supplying voltage in this way is prohibited by the USB specification, but it’s also not unusual – hubs such as this are used with the Raspberry Pi to power them without the need to attach a separate, independent power supply.
The issue here is that the Mac owned by the viewer who sent in the hub apparently has no protection to stop this backfeed. Such protection is not only common within computer hardware but also incredibly easy and inexpensive to implement via a simple diode.
Unfortunately Clive doesn’t know which model of Mac was used, or its age, although we can perhaps surmise that it was a model still within its warranty period if Apple replaced the motherboard. Therefore, it was perhaps a recent model.
Clive is skeptical that the Mac motherboard was in fact destroyed, and in a comment to Mac Kung Fu explains it’s more likely the backfed voltage caused the Mac to exhibit sleep or wake issues of some kind:
The person who sent me the hub had been helping someone else with their computer, which had been put to sleep three times by the hub and had to have its motherboard replaced each time. Having looked at other comments [on the YouTube video] I’m wondering if it was just being held in a sleep state by the presence of the 5V and if the repairs really involved swapping the motherboard or if the [Apple engineer] just reset and cleared it.
However, the message is clear: Mac users should avoid any USB hub that backfeeds via the uplink cable or, if you have no choice but to use one, use it in unpowered mode – without connecting a power supply to it. The model featured in Clive’s video is unbranded but has a distinctive 7 Ports Hub logo on top – see the photo below that I took, because as it happens I own two of them (which I use unpowered.)
Discovering whether any hub backfeeds can be difficult because it’s often considered a “secret spec” not mentioned officially. However, reviews of the hub by users sometimes discuss the ability, because users specifically seek-out hubs with this characteristic.