Questions about external USB power for Nano

I have a Nano that I would like to power via USB with a MP3/MP4 power supply, a tiny wall wart with a USB connector on it. I tried conecting it to the Nano. The Nano did power up, but the TX and RX LEDs were also on continuously. No permanent damage seems have occurred, but why were the LEDs lit? Is this bad for the Arduino?

I took the power supply apart and noticed that it connects USB pin 3 to ground, and has no connection on pin 2. Would it help to disconnect pin 3 from ground?

I don't see how it could hurt to try. You might also want to disconnect every pin from the supply except +5V and GND.

The Nano did power up, but the TX and RX LEDs were also on continuously.

I wouldn't worry about it. It's probably just a product of the onboard FTDI chip having power but not seeing valid USB D+ and D- data.

Lefty

Problem solved. As suggested, I cut the trace from pin 3 to ground in the wall wart. The TX and RX lights are now off.