Arduino doesn't boot unless I short USB pin 1-2 (VCC/Data -) I've made my own AVR programmer with an Arduino Nano V3 clone. It has been working fine, but yesterday I was trying to program a faulty board that pulled too much current. Was powering via USB and my OSX laptop told me it had disabled it due to pulling too much power.

After that I couldn't power it anymore, not even from a simple phone charger. I thought I had burnt something, but when testing with a DVM I accidentally shorted pin 1 and 2 of the USB connection:

1 - (red) VDC / plus / +5V

2 - (white) Data -



Then it boots up and is powered as long as I have them connected. Without it wont start with any usb connection, laptop or phone charger. Just to show what I mean:

https://photos.app.goo.gl/rtFj6bp3j4SbuYKr1

Why is this and is there something I can do to save this Nano - it seems to be working fine when usb is shorted like this…

Would hate to have to build up another one while waiting for a new programmer from China :)
When you plug the board in, the computer enumerates it. The normal device descriptor (IIRC) requests 50mA. If you are (as you most likely are) drawing more than that then the computer is quite within its rights to turn it off.

By shorting those pins you are preventing it from enumerating, so the computer doesn't know the requested amount, so it assumes (probably) 500mA.

You can achieve the same effect by using a cable with no data wires in it.