Hi, I found a non-SMD Arduino UNO R3 at school and it appears to have received incorrect voltages. When connected to the PC it is not recognized as an Arduino device but as an unrecognized USB device.
It also starts to overheat the elements marked in red in the photo. According to the professor, the previous owners would have inserted the wrong voltage through the dc21mmx connector.
Could anyone be able to tell me which elements to replace?
If any parts are getting hot, they are blown. (That's easy... And of course they can be fried and not overheat.)
In general, you never know what the problem is until it's fixed. And with an over-voltage or reverse-voltage situation multiple chips could be fried. 
You can check the voltages (5V and 3.3V).
And you can apply more than 5V to the barrel jack to check the 5V regulator. But if you don't get 5V, another shorted chip could be pulling-down the voltage so it's hard to know if it's the voltage regulator or something else. The voltage regulator can also overheat if the chip itself is blown or if something else is shorted.
Of course you can change the main ATMEGA chip, but it has to be already-programmed with the bootloader. And if you have another Arduino you can pre-program the chip with the Blink Example. If that works in your bad board but the USB still doesn't work, it's probably just a bad USB chip.
...I have a SMT Uno that died "for no known reason". I'm not good at SMT soldering so I didn't want to attempt a repair. I did try re-programming it with a stand-alone programmer but that didn't work so I just scrapped and replaced it. (I wrote "BAD" on it with a Sharpie and I keep it around for checking & measuring physical dimensions and that sort of thing.)
And, I try to keep a spare-working UNO on-hand.
Measure the resistance across the two capacitors you marked. If one or both of them are shorted, desolder them and check again.
If there is still a short even with the capacitors removed, desolder the two marked chips.
Plug in the USB (with the MCU still removed) and check if you have 5V between the USB shield and the fuse next to it. You can also check for 5V on the top-left and bottom-right pins of the ICSP connector in the picture.
If it is much less than 5V, look for other burned parts.
At the bottom of this page you will find a link to the schematic (and other useful documents).
To be sure, replace all the ICs, Processors, regulators etc and all the electrolytic capacitors, maybe the fuse as well. It can sometimes be quite difficult to work out which parts are duff until you replace them.
You could start by replacing the things that get hot, but you cannot be sure thats all thats broken.
Do you have any experience in PCB repair, SMT in particular ?
i don't have any experience, but i saw the price for the new components that failed and i decided to abandon the project.
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.
