hi!
i accidently set 12v on arduino mega 5v output pin. board still works and runs my program, but i'am not able to load any new sketches to it. TX / RX lights dont response and arduino IDE says timedout() etc.. when try to load new sketch in it.
i think there's nothing else to do that buy new one?
Exactly which board is it?
hi tomKi
it's the latest mega 2560, do you think that it could be fixed somehow.
board still works and runs my program,
So by some miracle you possibly haven't blown up the CPU, but maybe the USB CPU has gone poof?
If that's the case you may still be able to program the board using ISP.
If you're really lucky maybe you just blew up a regulator. Have you tried powering from the USB and also the VIN plug?
Rob
I would say that there is some chance. Can you see if you are actually getting five volts out of the regulator now? It might have been damaged and if it's wrong then one processing unit might work while the other one won't. It's not good for either one to run it like that.
Probably the only thing that you can do is change the five volt regulator, if it needs it. If you try to replace the ATMEGA8U2-MU chip, while it can be done, you will also have to get the firmware for it and program it before installing it. That's probably more trouble than it's worth. You should be able to program the 2650 chip through the ICSP connector but you won't get the USB back unless you either change the ATMEGA8U2-MU or finagle a USB connection. You could emulate it on the 2650 or connect an adapter.
@TomKi
Just looking at the Mega schematics and PCB. There is a separate ISP connector for the ATMEGA8U2-MU, the header is not loaded though. So it looks like you can program the chip in circuit.
Of course swapping such a small chip would be a challenge.
connect an adapter.
That would be easy to do with an FTDI cable.
Rob
thank you guys for answering!
it works with external power jack , USB and even via VIN pin, but i just can't load any sketches in to it.
no worries i buy a new one it's only 54€. shitty thing is that now is sunday and all shops are closed 
it's not worth to start changing some parts by soldering.
lesson learned do not prototype nothing middle of night. i build stepperMotor control with darlingtonArray on my breadbord and accidently i got mixed with wires so motor side power 12V got in control side 5V.
Looks like it's the ATMEGA8U2 chip then. Bummer.
Rob
The power from the USB goes directly to the +5 volts on the board, so you will always be able to power the board even if communications isn't working.
It's up to you of course, Hugo. If you buy or build a programmer that will work with the six pin connector you will probably have a usable board. I have an Arduino serial that I bought a board for and I didn't even hook up the serial port. Adafruit has the programmer built right into a USB cable for $20. There are inexpensive kits and plans all over the net. So if you ever feel like using it, that's how to do it.
Yes it almost certainly will still work with ISP, so for $20 you can resurrect your $70 Mega. Still buy a new one for development but when you have a working permanent project burn the code into the bad Mega and leave it in the project.
Rob