Arduino Micro Getting Hot

I made a circuit that has 4 switches that I wired like Arduino says to and the switches control 2 TIP122 Darlington transistors with a 1k resistor on the base. It also has a potentiometer. I originally built it on an Uno and it worked fine. Then I wanted to shrink down the size of the project so I got an Arduino Micro from Amazon: http://www.amazon.com/Arduino-151185024-Micro/dp/B00AFY2S56/ref=sr_1_2?ie=UTF8&qid=1393809509&sr=8-2&keywords=arduino+micro I left the circuit alone and simply switched out the Uno for the Micro. I ran the Micro on USB power and I noticed that within 2 seconds, the processor (not the regulator) got so hot that I couldn't touch it for more than a few seconds. I thought nothing of it for a 2 days because the project was working fine. Then, i went to power it up again, and the blue light lit and then faded away. I measured the 5v pin and it started at 4.2v and gradually dropped to 2v. My best guess is that the transistors took too much power but the Uno and Micro both have the same power rating and it worked fine of the Uno. Does anyone know why this happened and how it can be prevented from happening again?

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You did something wrong but all you have supplied is vague arm waving explanations of what you tried. You need to supply a schematic of what you did and how it was powered.

Two possible causes: reversed power connection or latch-up.

Latch-up: if you violate the voltage limits on the input/output pins (to be between 0V and Vcc +/- 0.3V) you can send any CMOS chip into latchup, which turns the entire chip into a heater - kill the power fast enough and it might survive.

Modern chips are more robust than older CMOS designs, but over-large currents into the protection diodes will do this eventually.

There are other ways this could happen, but these are known issues.

Its always a good idea when commissioning a new circuit to use a bench power supply with a programmable current limit - saves money in the long run!

The only time I've encountered this issue was when I was using the wrong resistor value on the base of the transistor.... not happened since