user37: I was communicating between my computer and my Arduino Uno R3 through Bluetooth using this Bluetooth module. The connector I use has a red wire where it connects to GND, and a black wire where it connects to +5V.


                ↓        ↓  to Uno ↓       ↓
               +5V      GND       pin 0  pin 1


I forgot this one time when I connected the Bluetooth module to the Uno, so the polarity was reversed. This fried the Bluetooth module.
After getting a new module, I discovered that the Uno was apparently fried too. Plugging a USB cable into the Uno made the little green integrated LED turn on, but that was all that happened; none of the pins put out any electricity. When I tried to upload a program, it gave the infamous avrdude: stk500_getsync(): not in sync: resp=0x00 error. I could upload programs to my other Uno fine, and I could not upload to the broken Uno on my other computer.
Two of the Arduino experts I know told me that the ATmega328 chip might be the only broken part. Is this likely to be the case? I have an Uno R2 with a working ATmega328. Would temporarily replacing the R3's ATmega with that R2's ATmega have a change of damaging anything?

user84: Besides breaking a pin while removing the IC from its socket, or static electricity during manipulation, I don't see what could fry the ATmega. 
However, it is possible that the R2 ATmega has a different bootloader and that may be an issue.
If I was you I would just remove the ATmega from the R3 board and test it on a breadboard (don't need a lot of components to do that); at least that could tell you if it is fried or if it is the R3 board that is fried...

37: <p>I was communicating between my computer and my Arduino Uno R3 through Bluetooth using <a href="http://www.mdfly.com/index.php?main_page=product_info&amp;cPath=8_47&amp;products_id=769&amp;zenid=6f2b3946847b73b5ef2185e5e756e498" rel="nofollow noreferrer">this Bluetooth module</a>. The connector I use has a red wire where it connects to GND, and a black wire where it connects to +5V.</p>

<blockquote>
  <p><img src="https://i.stack.imgur.com/upJ7C.png" alt="enter image description here"></p>

<pre><code>                ↓        ↓  to Uno ↓       ↓
               +5V      GND       pin 0  pin 1
</code></pre>
</blockquote>

<p>I forgot this one time when I connected the Bluetooth module to the Uno, so the polarity was reversed. This fried the Bluetooth module.</p>

<p>After getting a new module, I discovered that the Uno was apparently fried too. Plugging a USB cable into the Uno made the little green integrated LED turn on, but that was all that happened; none of the pins put out any electricity. When I tried to upload a program, it gave the infamous <code>avrdude: stk500_getsync(): not in sync: resp=0x00</code> error. I could upload programs to my other Uno fine, and I could not upload to the broken Uno on my other computer.</p>

<p>Two of the Arduino experts I know told me that the ATmega328 chip might be the only broken part. Is this likely to be the case? I have an Uno R2 with a working ATmega328. Would temporarily replacing the R3's ATmega with that R2's ATmega have a change of damaging anything?</p>
 84: <p>Besides breaking a pin while removing the IC from its socket, or static electricity during manipulation, I don't see what could fry the ATmega. </p>

<p>However, it is possible that the R2 ATmega has a different bootloader and that may be an issue.</p>

<p>If I was you I would just remove the ATmega from the R3 board and test it on a breadboard (don't need a lot of components to do that); at least that could tell you if it is fried or if it is the R3 board that is fried...</p>
