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Connect my Pi model B to mac USB port. The power LED remains off. There is excessive amount of heat generated at the component highlighted in the pic. Any idea how to resolve? enter image description here

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Two possiblities: 1. You were doing something with it before this happened that means something has broken or burnt out. 2. Your Mac USB port isn't generating enough power to power the Pi. I'm not putting this as an answer because without further information as to what you were doing beforehand, I can't really give you a definitive answer. – recantha Feb 17 '13 at 12:36
Thanks, what I forgot to mention is that it booted once on the same usb port. I was able to ssh into it for 5 minutes. But after that it just kept on failing. I have another Pi connected and connecting to the same port and with the same cable and it is working fine. – Kenny Lu Feb 17 '13 at 12:47
can you measure the voltage across the test points? – nc4pk Feb 17 '13 at 14:34

I think that component is an LDO regulator. It getting hot might indicate excessive voltage from your supply.

It is also near the F3 polyfuse (look underneath the board toward the corner, you'll see the F3 label).

If the PSU is unregulated it can also output too high a voltage, which may trigger the overvoltage device in the PI, which will temporarily short the 5V to ground, this will then "blow" polyfuse F3, which will take several days to recover from. Meanwhile (possibly with another PSU) the PI might not get enough power because the (partly) blown polyfuse is consuming some of the power. The solution is when this happens to ways a few days to give the polyfuse time to recover before attempting to use the better PSU. If you suspect a blow polyfuse, measure the voltage across F3, which should be less than 0.05 Volt.

From http://elinux.org/Rpi_Hardware#Power

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Yes, excessive voltage or just broken from ESD for example. – Gunnish Feb 18 '13 at 10:30

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