Arduino Ethernet issue


I'm using an Arduino Ethernet board (not the shield) and the Ethernet connexion is not working anymore. TX/RX leds are not blinking when an Ethernet cable is plugged and ping doesn't success either. Everything else works, just seems like W5100 is not answering as it was used to.

I've done several projects before with the ethernet port and worked fine, does anybody know if I can try some troubleshooting to fix this?

Many thanks in advance!

If the sketch is working, try a new ethernet cable. Or take a very good look at every soldered pin of the ethernet connector and near it with a magnifier.

The ethernet chips use more power than any other chips. Perhaps a voltage regulator or capacitor got too hot. Measure the voltages. The ethernet chip runs at 3.3V.

Everything else works, just seems like W5100 is not answering as it was used to.

What do you mean by “everything else works.” What other tests have done to make sure your code is working fine? What code are you using?


Many thanks for both answers. I've tested every pin and as far as I can understand it seems fine, but still no answer from the Ethernet.

What do you mean by "everything else works." What other tests have done to make sure your code is working fine? What code are you using?

I ment that any simple code was working fine (blinking leds, controlling servos, reading temperature sensors, accelerometer, etc), until weird symbol readings started to appear at my monitor serial and suddenly I couldn't receive anything at all (at serial). I'm using a USB to serial adapter.

After not being able to receive anything, I've unplugged only the 5v pin from the serial adapter and used and external power, then serial readings where working again (seldomly with weird symbols as well).

Is my Arduino dying slowly? xD

WS5100 is getting really hot, but I think it works at relatively high temperature (around 80ºC?)

Many thanks again!! (and sorry for my english)

Edit: I forgot to say that I tryed differents ethernet cables and also nothing.

80 degrees Celsius is about the limit of what is normal. Do you have a IR temperature meter. I bought one on Ebay for a few dollars and it turned out to be very handy to determine a hot spot on a board.

Perhaps when powering with USB, the voltage was too low for the Arduino. Perhaps when using the external power supply, the voltage regulator got too hot and turned down the current.

Can you measure the 5V pin of the Arduino board ? It should be between 4.5V and 5.0V.

Hi Erdin, thanks for your answer.

Yes, voltage at 5V pin is 4.7-4.8V so seems ok, so the voltage regulator should be fine right? Also the 3.3 pin is ok and Vin pin measures the 11.0V I'm puting at the jack connector from external power as well.

Anyway the power through USB was always fine before, but it's obvious that something is wrong if I can read Serial data unplugging the 5V connector of the USB-serial adapter and weird symbols appear at the serial monitor.

About the temperature, I will try to measure it and confirm if it's too hot.

Will let you know, thanks!

The W5100 draws 200-300mA of current. That chip alone means the onboard regulator is burning (11V-5V)*200mA = 1.2W.

It is very likely the chip, the ATmega328, and whatever else your project has connected is causing the regulator to go into thermal shutdown. If you have a power supply that outputs 9V or a better external regulator to provide 5V you may get more stable operation.


Thanks for your answer, I tested the temperature and there is nothing beyond 70ºC, so I don’t know what’s going on. The board works fine, only the ethernet is down. I’ve got a new Arduino Ethernet and loaded the same project with the same pin configuration and it’s working perfectly (Controlling servos with OSC protocol).

I am using external power, a 9V battery which is not giving any problem with the new board, and seems to do the same with the old one (except with the ethernet).

Maybe the W5100 got burned and now is just not working properly? even if temperature now is “normal” and Voltage values are correct?


Tibali: a 9V battery

What kind of 9V battery? Certainly not one of those small rectangular batteries only designed for 25mA of operation...

hehe no, it is a 9V and 1200mAh battery.

Yeah, sounds like the W5100 itself was damaged.