1.7v on 5v pin: regulator gone?

Hi there,
digging around I've found an Arduino Mega just laying there, so I tried to hook it up to my 3D printer (been brainless for a while). Since the connections should be good but there's something not working as intended, I've checked the board.

While powered through USB, the onboard LED lights up and the 5v pin outputs circa 4.8-4.9V.
When powered through a battery pack (4x1.5V) it outputs only around 1.7V, and no light from the onboard LED.

Should I check in another different way, or is this enough to say the regulator is faulty?

Thanks in advance! :slight_smile:

As a final check stick a 9 volt supply to the barrel jack.
I just don't trust battery packs as a real test.


Why would you connect a power supply to the regulator input?

For any actual application, you need a 5 V supply, connected to the "5V" pin or (second best,) USB jack.

6V to the regulator should arguably, output about 4 V or so. Of course, you did measure the voltage of the battery pack itself when you connected it?

Sorry for the late reply folks!

@ballscrewbob I'll do that just to be sure

@Paul_B I'm not sure I understand what you mean... I haven't connected the power supply to the regulator pin, I don't even know what you're talking about tbh!
I simply took a battery pack, stick it to the external power supply connections, then tested the voltage accross a GND pin and the 5V OUT pin..

But yeah, as I thought you're saying the output I'm measuring far less than expected
(I did test the pack even if the batteries are new, of course)

The external power jack feeds a linear regulator with a certain voltage overhead - so normally it needs 7V or more to guarantee 5V output from the regulator. To get only 1.7V out would imply a lot less than 7V on the input.

It suggests the 6V battery pack is dropping right down in voltage under load.