I've been trying to resurrect an old project that uses an 8x8 grid of sparkfun LED button pads. Its powered from the teensy (there's no external power involved) so I'm guessing I've shorted something at some point. I'm only seeing around 2.2v on the VUSB and around 1.9v on the 3.3v pin. I can see the full 5v on the USB side of the fuse but the lower 2.2v on the other side of it. The regulator/fuse area is also getting hot.

I've removed the teensy from the circuit and still get the same results. I can connect it to a PC and program it - putting the blink example on gives the same result although the led is blinking so it looks like code is running. I can't see any shorts between ground and VUSB or the 3.3v pin.

Any suggestions of things to check for? Is it possible that I've killed the fuse? If the regulator area is damaged could I still power it with a 3.3v supply?