Arduino Uno outputs 8V when pin is set to HIGH I am doing the following in setup:

 pinMode(13,OUTPUT);
 digitalWrite(13, HIGH);


When I check with the multimeter, I get an output voltage of 8V rather than 5V. What may be the problem and how do I troubleshoot it?.
You have a badly calibrated multimeter. 

Try it on something where you know what the voltage should be, such as a 9V battery and see what it reads.