Hey,
Im using an ARDUINO-Duemilanove.Last night i burned a program which involved reading sensor values to analog input and viewing it on the serial monitor. I made a slight modification in code and tried to burn the program but none of the lights were lit up in the board and an smd component "5x5", close to the USB jack heated up almost instantly.It doesnt seem to work anymore. What went wrong? Is there any fix?
thanks
That Component is (was) the Fuse for the USB, and it has obviously been blown. It's not Impossible to fix something like that , But I will say you are going to need a steady hand with a soldering iron.
With any luck, the fuse did it's job and protected the other components down the line, like the little USB controller chip.
Have you tried powering up the board from an external source?
Of course, now you gotta figure out WHY the fuse blew. I assume the board was hooked up to your project at the time. Is there any chance something may have been shorted out?
If this meens anything to you.. the way you describe the fuse sounds exactly like the one on my defective counterfeit UNO board.. green with 5x5 on it? the one on my authentic board is black with 501k written on it. when my board fried, it took out the USB controller chip, but the fuse was intact. I KNOW I shorted my board and the computer screamed USB over voltage and shut down the port. by that time the damage was done however, and I can only program it via serial.
So... all may NOT be lost.
If you have a meter, check for continuity across the fuse. if nothing, then yes, it is blown. Also check for voltage by plugging in the USB cable. between the case ground of the USB jack and either side of the fuse. if you only get it on one side? then the fuse is dead
Disconnect everything from the board and see if starts to function again. If so, it helps to indicates a short circuit.
That Component is (was) the Fuse for the USB, and it has obviously been blown. It's not Impossible to fix something like that , But I will say you are going to need a steady hand with a soldering iron.
How do i replace the fuse? Like will i be able to buy it or something?
Have you tried powering up the board from an external source?
Havent tried that , will give it a shot. 
Of course, now you gotta figure out WHY the fuse blew. I assume the board was hooked up to your project at the time. Is there any chance something may have been shorted out?
The only conclusions i could draw was maybe the 5v and the ground accidently or shorted or there was static from the computer.If it was bad earthing just to be safe i ran a parallel earth from the 3 pin to the ground, now.
by that time the damage was done however, and I can only program it via serial.
how did you do that?
If you have a meter, check for continuity across the fuse. if nothing, then yes, it is blown. Also check for voltage by plugging in the USB cable. between the case ground of the USB jack and either side of the fuse. if you only get it on one side? then the fuse is dead
I checked for continuity, it was continous. But while plugging in the USB i checked for voltage just like u said and i got a 5v on one side. So the fuse is really blown?
Disconnect everything from the board and see if starts to function again. If so, it helps to indicates a short circuit.
Nope, it isnt working. 
jayakrishnan:
The only conclusions i could draw was maybe the 5v and the ground accidently or shorted or there was static from the computer.
It is very unlikely your PC was the source of the problem. It is most likely you accidentally shorted 5V to Ground (and that short is still present.) The Fuse used on the Arduino is a "Poly Fuse." Once it cools down to room temperature, it should conduct again.
jayakrishnan:
If it was bad earthing just to be safe i ran a parallel earth from the 3 pin to the ground, now.
Digital Ground is not Earth Ground. I have no idea what you think you were accomplishing by connected a pin to ground.
You've created a short circuit somewhere. Either a chip has gone bad or there is still a short somewhere on your board.
How can I verify my USB controller is blown? How can I replace it? Uno.
sbright33:
How can I verify my USB controller is blown? How can I replace it? Uno.
Start your own thread? This has nothing to do with this one.
Or you could just follow the loop-back instructions which are sticky on this section of the forum.
@james you were probably right, the arduino actually works now. Thanks a lot for replying to this post.