Ethernet Shiled not working when not powered via USB

I have a strange one that I hope someone can help me with.

I have a original Arduino Duemilanove with an old Ethernet Shield connected to two LED’s and a Thermal Printer. Circuit is attached to this post. The Thermal printer needs 1.4A so I have a 9V 2.2A external PSU supplying power to all of this.

While I was developing the code I had the USB port plugged in and everything worked great. Now that I have stopped developing I unplug the US and the Ethernet Shield won’t connect to the network!? :~

The Arduino itself is working fine, the printer is working fine, but the Ethernet shield won’t setup the link. I can’t easily debug further as that would involve having the USB cable plugged in which makes everything work :slight_smile:

I’ve checked the 5V line and the 3.3V line which are both perfect.

I’ve done some reading and one suggestion is that as I have a load across Vin that this can damage the regulator. Could that be happening here?

Any help greatly appreciated.

Thank you

Your 9V power supply is fine. It's close to the ideal voltage to be supplying to Vin.

I'd check the voltage between the 5V pin and GND just to verify there's no problem with your 5V regulator. Beyond that I'd doublecheck your code to make sure you didn't write anything that will hang if there's no hardware serial connection present.