Sorry guys, but that's BS. Why should he have to replace the motherboard because of a software brick?
The OP was very silly and I'm not sure if he has the expertise needed to unbrick his device, but it is possible.
This is just a dead bootloader it seems.
Luckily there's even the official Samsung dead phone repair guide available, which has been used to create the solution
in this thread (SD-Bootloader-repair-method, one working i9300 is needed):
I've not tested this solution myself since I work with jtag boxes, but according to many posts it is valid.
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