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I just received an Arduino ATmega2560 (GEEKCREIT). The 5V interface is giving exactly 5V as expected.

But on the 3.3V interface I could only measure 0.23V. What could be wrong?

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    \$\begingroup\$ did you connect anything to it? \$\endgroup\$
    – Eugene Sh.
    Oct 17, 2017 at 21:02
  • \$\begingroup\$ No, I'm measuring the 3.3V pin and ground directly on the board with a multimeter. \$\endgroup\$
    – alesko
    Oct 17, 2017 at 21:08
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    \$\begingroup\$ Then it is probably broken. Try measuring on the 3.3 regulator directly \$\endgroup\$
    – Eugene Sh.
    Oct 17, 2017 at 21:15
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    \$\begingroup\$ It might just be a bad board, you don't get much QC for $10... You might also try using the other power input (USB / barrel connector) just in case it is not an exact copy of the Arduino Mega. The little SOT23-5 between the crystal and the processor is probably the 3.3V LDO, you might try following the traces, finding the input and output and checking the voltages. Also check the temperature of this chip in case the 3.3v output is shorted somewhere. \$\endgroup\$
    – Dean Franks
    Oct 17, 2017 at 21:18
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    \$\begingroup\$ Either your source is bad or your load is too high \$\endgroup\$
    – Voltage Spike ♦
    Oct 17, 2017 at 21:26

1 Answer 1

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The first thing to verify is the 3v3 regulator, you could start measuring voltages at the IC6 pins (3v3 regulator). Connect the negative probe of a multimeter to ground. Put the positive (red) probe in the IC6 pins. There should read 0V at pin 2, 5V at pin 1 and pin 3, and 3v3 at pin 5.

arduino 2560 schematic arduino 2560 showing IC6 enter image description here

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  • \$\begingroup\$ I've put ground on IC6 pin2 (from schematic on top) and positive on pin5 and get -4.64V. The rest of of pins read 0 and pin3 resets the device. \$\endgroup\$
    – alesko
    Oct 18, 2017 at 0:01
  • \$\begingroup\$ Note that pins 2 and 3 are swapped in the schematic. Use the pin numbering mguima supplied at the bottom of his post. Assuming you had your negative probe on EN and positive on +3.3, it looks like your regulator is bad. \$\endgroup\$
    – evildemonic
    Oct 18, 2017 at 0:37
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    \$\begingroup\$ @evildemonic Thanks for the info. I measured it now correctly. pin 5 has 0.24V and pin 1 has 4.9V. So the regulator is defective. \$\endgroup\$
    – alesko
    Oct 18, 2017 at 16:11

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