I gave 7.5v to the arduino mega board through battery. 5v pin in the board gives me the same voltage as input. Earlier it was working fine now it is giving problem.Please let me know the solution as soon as possible.
Thanks and regards, Thippeswamy
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It is highly likely that you have destroyed your Arduino. This can happen in a number of ways. Rugged Circuits has a great article on 10 ways you can destroy the Arduino.
The giveaway is that you are measuring 7.5V on the 5V pin. Most likely the voltage regulator has blown. Page 355 of the ATMega2560 datasheet says the absolute maximum voltage for the chip is 6.0V, so this also means that the microcontroller is blown as well. It is most likely unsalvageable.
Go out and buy yourself a new one. Before you turn it on, check the wiring is correct.
We have all let the magic smoke out at some point.