12v in 3.09v out Arduino Uno, fixable?

If I power the Uno via USB the 5v pin reads 5v, as expected.

If I power the board through Vin or the barrel adapter with 12v, the 5v pin reads 3.09v.

If I power the board through Vin with 12v and USB, the 5v pin reads 4.5v.

No other pins connected.

Is there a way of fixing this board?

uglyfish:
If I power the Uno via USB the 5v pin reads 5v, as expected.

If I power the board through Vin or the barrel adapter with 12v, the 5v pin reads 3.09v.

If I power the board through Vin with 12v and USB, the 5v pin reads 4.5v.

No other pins connected.

Is there a way of fixing this board?

Welcome to the Arduino forum.

What else is connected to the Arduino? What are you using to read those voltages? Are you reading them on the actual Arduino pins and Arduino ground, or on a bread board?

Paul

Hello, thanks for the welcome and the reply.

No pins are connected to any peripherals.

I'm reading with a voltage meter in DC mode, reading 3.09v from 5v and ground pins directly, while powered by barrel adaptor to 12v (12.31v verified).

Sounds like your 12V adapter is either too puny to power even a naked Arduino or is putting out AC. Have you checked the voltage with your meter on AC Volts?

Adapter is 12v 1a. The 5v pin shouldn't be putting out AC current, should it? I also know that the USB power circumvents the voltage regulator. I'm suspecting a faulty voltage regulator. My question is now, could it be anything other than the voltage regulator?

I meant, did you check the 12V adapter's output WITHOUT it connected to Arduino (or anything else), check for AC voltage and a too high DC voltage, (means it's unregulated).

Sounds like your voltage regulator on the arduino is not doing what it should. The 5v coming from usb directly bypasses the regulator so it will read the usb voltage. If nothing is plugged in the 5 volt reg is the most likely culprit.

outsider makes a good point though. Check the adapter for function and to make sure it wasn't the cause of the regulator dying.

I've tested the power supply and it is OK, no AC reading, 12.31V DC. Will try to change the voltage regulator. Thanks all for the help.