You know that microUSB cable that was neatly tucked away inside the box that originally held your HTC EVO 4G? Well, you might want to unplug it, throw it in the trash, take the bag to the curb, wait for it to get picked up, follow the garbage truck, and make sure you see it in the dump.
According to G&E reader StacyD, the computer engineer who you may remember from last month's speaker light mod, the cable was engineered improperly using a cheap panel mount/board mount hybrid connector instead of a proper microUSB cable mount-style connector. I'll let StacyD explain this in technical terms below but the bottom line seems to be this: the cable is a fire hazard and you shouldn't use it.
That's StacyD's boyfriend's cable you're looking at above but hers met the same fate a few weeks ago and burned her fingers/hand.
What kind of wild and crazy thing were they doing with the cable when it started melting? Oh, just using it like everyone else does.
What she did with her cable:
- Plugged the USB end into her computer at work
- Grabbed the microUSB end so she could plug it into her EVO
- Touched metal shield, which was hot enough to burn her finger
- Immediately removed the cable
She then opened the cable with an Xacto knife. The wires and wire connections were fine, but the connector shield (metal part that plugs into EVO) had slipped off the internal plastic base because the rubber was too flexible. She told me in an email that this means "the shield had gotten loose (not loose enough to fall off or anything, just loose on the inside of the connector). This gave it enough wiggle room that it made contact with the 5V power pin as well as the GND pin, as they are further out that the data pins on a microUSB connector.
What he did with his cable:
- Plugged the USB end into his Lenov0 W510 at home
One night last week after the couple ate dinner, they smelled burning rubber and discovered that the cable, still plugged in, "was bubbling and he had a big warning message on his laptop screen." They removed the calbe and shut down the computer.
StacyD tested the cable and found that it "had shorted at the pins due to the shield," just like hers did a few weeks before. The digitial multimeter readings taken with a Fluke DMM were as follows:
- USB shield to GND: 0.1 ohm
- microUSB shield to GND: 0.1 ohm
- 5V power line to GND: ~27 ohm
The ~27 ohm reading makes sense, she says, because "sometimes companies put limiting resistors in the plug (Motorola does this with the Droid and Apple does this to help identify 'authentic' products)."
Here's how/why this happens, in StacyD's own words (boldface added for emphasis by me):
What happens is that since the connector shield/metal outside part is not secured beyond two small points, any movement of this shield can cause a temporary dislodging and have the GROUNDED shield touch the 5V power line on the USB cable. Most modern laptops and desktop computers put out between 500-1000ma of current at 4.5-5.5V which means that you could be having as much as 5.5Watts burning through those cable lines and melting the crap out of some rubber as in this case.
As you can probably imagine, a lot of very bad things could happen when you've got up to 5.5 watts just quietly burning through cable. In addition to burning you or someone else, it could damage whatever it's plugged into—StacyD cites the possibility of burning out your computer's USB receiving chip or the power diode for the USB—and of course cause a fire. I don't know about you, but the area surrounding my computer is pretty flammable!
Could this have been prevented? Absolutely. All HTC had to do was use a "larger isolated and secured connector" or "hard ABS plastic instead of flexible rubber to secure a metal part."
The good news, if you want to look on the bright side, is that it's just a standard microUSB cable. The EVO doesn't use some sort of special proprietary connector, so finding a replacement cable that won't burn down your house is easy and will only cost you a few bucks.
If you don't know where to look, there's a fine selection at Amazon, in the bargain bin at your local electronics shop, and probably in the back of your desk drawer.[Does It Pew?] Thanks, StacyD!