Hello, a friend of mine gave me his faulty raspberry pi for free, and now i want to try and repair it. I took the sd card of my known working personal raspberry pi, installed it, and sure enough the faulty raspberry pi booted right up, hdmi and ethernet were working perfectly and I could ssh into it. However, i noticed none of the usb ports were working, no power at all was given to any usb device i tried.
After some investigating, I found that dmesg gives me a long list of "usb 1-1-port2: over-current change" errors.
I then got my multimeter out and tested for power on the USB ports, but PP27 reads around 100mV when it is supposed to be 5V.
I did some more research and some threads suggested that maybe C97 was bad, so I tested the resistance between the two sides of the capacitor and it was reading close to 0.6Ohm, so I removed it, but then the same problem still persists.
Probing the two pads on the board where C97 used to be still gives me close to 0.4Ohm, and probing from PP27 to ground gives me a resistance of around 0.4Ohm also.
To my eyes there is clearly a short between PP27 and ground, but I don't know where it is... I thought about applying an external voltage on PP27 and ground to find if any component would heat more than the others and use some isopropyl alcohol to locate it (saw this on rossmann vids) but I'm afraid I'm gonna fry something on the board...
Could anyone help me on how I should diagnose this problem? All help is greatly appreciated!!!