I have accidentally changed the fuse bit SUT_CKSEL of an Arduino mega 2560 from 'Ext. Crystal Osc. 8.0- MHz; Start-up time: 16K CK + 65ms' to 'Ext. Clock; Start-up time: 6 CK + 65ms'. The board has become unresponsive now. (I was programming through AVR ISP programmer, AVR Studio)
I have tried a lot browsing to find the fuse recovery of an arduino board but no solution. Can anyone please help me in recovering the SUT_CKSEL fuse bits ?
I had the same problem quite some time ago. What I did was to temporarily connect a thin wire (a piece of wire-wrap wire) to the 16U2 chip (pin 2) and to the XTAL1 pin of the 2560 (pin 34)
To get at these, the easiest points are:
(1) The 1M resistor (R2) across the crystal for the 16U2 chip, closest to the 2560 chip
(2) The 1M (R1) resistor across the resonator for the 2560 chip, the side closest to the headers
Carefully tack solder the wire and don't touch it while re-flashing the bootloader (because your finger will load the crystal and may stop it).
What this does is send the XTAL2 (output) from the 16U2 chip to the XTAL1 (input) of the 2560 which will allow re-flashing.
Then, remove the wire and you should be good to go.
Hope this helps.