This is kinda weird problem. I used Raspberry Pi A+ for my small projects. I did all the programming using a USB WiFi dongle via SSH. It all went happy and fine until one fine day the dongle stopped blinking (which indicates, no activity. Normally, it has a green LED which blinks when the dongle is working properly). I plugged that dongle on my desktop PC and it worked there. I tried using a different dongle which didn't work on my Raspberry Pi but was working fine on my PC. I even did lsusb test, which couldn't detect my dongle (earlier it showed 'Realtek' for my dongle). I got the verbose output and found that USB current was 0mA.
I plugged a USB flash drive in my RPi. It turned on, but wasn't recognized by the RPi. It indicated that the power lines were fine.
I had a doubt that something was wrong with the USB port on my RPi. I removed the dongle, grabbed my multimeter and did some continuity test. I found that both the USB data lines of the RPi were shorted and grounded. I thought some dust and moisture might have stuck inside and shorted them all to the ground. I dried and blew warm air, cleaned the contacts, yet it was the same. I had a spare USB female port. So, I desoldered the original port and replaced it with the one I had. I even previously checked that the data lines of the new one were not shorted. Yet, the problem reproduced.
I'm still dumbfounded and don't know what's wrong with the USB. I surely checked all the test points and circuit lines and couldn't find anything shorted.
Anybody knows what could be the problem?
lsusb -ton the RPi with something plugged into the USB port in order to see what the system sees. – WineSoaked Aug 9 '15 at 23:33