So I have a Arduino Mega 2560 and when plugged with USB, only TX led blinks . With a 11V battery in the Barrel, any led works. However, in the Vin pin I read 11V, and in the 5V pin I read 4.7V Nothing is connected to the board. Also, when connected to USB the PC recognises COM 8 as arduino UNO.
Is "on" = "Power" or "L"?
Probably a sketch is already uploaded and is using the TX port (and not the "L" LED. Write a new, basic, sketch and upload it.
Now any led turns on. Connected with USB I mean
Try another USB cable. (I assume "any" means "not any")
The cable is OK because with a UNO board works perfect. Yes, no led lights up
Try another COMM port (if you suspect bad power).
So when I upload a sketch the TX and RX leds work. But when I unplug and plug again all leds are off. After 20 seconds the TX led starts blinking.
After uploading your sketch, does the sketch work? Is your code using the TX pin?
Post your sketch. Do not forget to place it in code tags for the forum. Please read the forum introduction, as you were asked to do when you joined the forum.
The thing is that I don't have any sketch. I just uploaded a blank sketch. The same sketch you have when you start the arduino app.
What happens when you upload the Blink sketch? It's the default factory sketch, not the Blank sketch.
Why do you care what the TX LED is doing?
TX LED doesn't matter, what I matter is the ON led. Why is always off?
Refer to post #2. Please post a clear, close up photo of the area of your board where the LEDs are, and identify all of them for us somehow.
If your ON LED is off, and the system is running, there is just some solder joint open or something like that. But it is hard to diagnose using just words.
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