Arduino Nano 3.3v pin Not Working

Got 2 Arduino Nano 5v versions from ebay (so they are arduino clones)
Using them in a wireless project

One of them is fine and the other has no voltage at all on the 3.3v pin

the code used in it until i realeased this problem recently is

#include <SPI.h>
#include <nRF24L01.h>
#include <RF24.h>
#include <DHT.h>
#include <LowPower.h>

#define DHTPIN 7
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);

char thChar[32] = "";
String thString = "";

float hum;
float temp;

RF24 radio(9, 10); // CE, CSN
const byte address[6] = "00001";
void setup() {
  Serial.begin(9600);
  radio.begin();
  radio.openWritingPipe(address);
  radio.setPALevel(RF24_PA_MIN);
  radio.stopListening();
  dht.begin();
}
void loop() {
  hum = dht.readHumidity();
  temp = dht.readTemperature();
  thString = String(temp) + String(hum, 0);
  thString.toCharArray(thChar, 12);
  for (int i = 0; i <= 3; i++) {           // Send the data 3 times
    radio.write(&thChar, sizeof(thChar));
    Serial.println(thChar);
    delay(50);
  }
  for (int sleepCounter = 4; sleepCounter > 0; sleepCounter--)
  {
    LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);
  }
}

Does anyone know what may cause there to be no voltage on the 3.3v pin or is it a hardware issue?
i was looking at this code and wondered if the “ADC_OFF, BOD_OFF” for the sleeping might have left something off leading to this no voltage on the 3.3v pin issue?
Any help would be much appreciated

Most Nano clones use the CH340 UART adapter (on the bottom side of the board), and it's that chip that provides the 3.3V source. Pin 4 of that chip I believe. If you can still communicate with the Nano, then it may be that the 3.3V regulator inside the CH340 has died. But if you measure 3.3V on pin 4, then there may be a broken trace between that pin and the 3.3V pin of the Nano. This link has good information on original vs clone Nanos, and has a good schematic of the clones.

http://actrl.cz/blog/index.php/2016/arduino-nano-ch340-schematics-and-details/

In theory you might be able to replace the CH340, but it would probably make more sense to just replace the Nano. But there's nothing in your code that has any effect on this. If the Nano has power, you should have 3.3V. But please note that only limited current is available from the 3.3V pin. The link has information on that.

1 Like

ShermanP:
Most Nano clones use the CH340 UART adapter (on the bottom side of the board), and it's that chip that provides the 3.3V source. Pin 4 of that chip I believe. If you can still communicate with the Nano, then it may be that the 3.3V regulator inside the CH340 has died. But if you measure 3.3V on pin 4, then there may be a broken trace between that pin and the 3.3V pin of the Nano. This link has good information on original vs clone Nanos, and has a good schematic of the clones.

http://actrl.cz/blog/index.php/2016/arduino-nano-ch340-schematics-and-details/

In theory you might be able to replace the CH340, but it would probably make more sense to just replace the Nano. But there's nothing in your code that has any effect on this. If the Nano has power, you should have 3.3V. But please note that only limited current is available from the 3.3V pin. The link has information on that.

Ahh Thank you
I did not know thats were the 3.3 volts came from
Did a little testing and sure enough there is nothing at Pin4 of that chip (there is 3.26V at pin4 of the chip on the other nano) so broken voltage regulator inside the chip

The other possibility is that the capacitor from pin 4 to ground has failed short, or there's a short to ground somewhere between pin 4 and the Nano "3.3V" pin. Such a short would give you a zero volt reading even if the CH340 is trying to output 3.3V. You might try disconnecting the Nano from all power, and testing the resistance between the 3.3V pin and ground. If it's very low resistance, there could be a short somewhere. Or you could carefully desolder and lift pin 4 from the board, and see if it still has zero volts when you power up.

ShermanP:
The other possibility is that the capacitor from pin 4 to ground has failed short, or there's a short to ground somewhere between pin 4 and the Nano "3.3V" pin. Such a short would give you a zero volt reading even if the CH340 is trying to output 3.3V. You might try disconnecting the Nano from all power, and testing the resistance between the 3.3V pin and ground. If it's very low resistance, there could be a short somewhere. Or you could carefully desolder and lift pin 4 from the board, and see if it still has zero volts when you power up.

Checked and there is no continuity or resistance between pin 4 and ground

Ok, well it sounds like it's just a bad CH340 chip. Or possibly you shorted the 3.3V output to ground and blew out the regulator. Anyway, if you need the 3.3V, the best option is probably to just get a new Nano.