Nano Works Standalone but not on PCB

Have a PCB with a Nano socket and the Nano's +5V is used to power some PCB components. Power path is... 12V -> PCB -> 9V regulator -> Nano's Vin and several opamps on the PCB. Nano's 5V pin is used as pull-up for three LEDs and to power a MAX485 RS-422/RS-485 Interface IC. Total draw from Nano's 5V should be less than 200mA.

The Nano and its code were working fine. Uploaded a new version of code while Nano was in PCB without PCB power applied and upload didn't work (no Tx/Rx LEDS lit) and then with power applied to PCB, which supplies 9V to Nano's Vin. Then the trouble began...

Now when in the PCB, the Nano does not function. Power light is on but code does not appear to run... no LED activity on the PCB LED that's attached to pin 13. When removed from the PCB, it successfully uploads and runs a BlinkLED sketch that flashes pin 13 onboard LED.

Suspect there's an issue with the Nano's 5V regulator or its Auto Power Select diode D1, preventing the ATmega from getting a good 5V. Plan to measure D1 and then 5V pin when Nano in PCB and powered.

What else should I check?

So just got back to this... Off the PCB, Nano connected to USB uploads and runs fine, at least a Blink sketch. Powered by 9V at Vin off-PCB, runs the Blink sketch but... the Nano's 5V pin is reading 8.3V! With USB, 5V pin is 4.6V (expected).

So, think the onboard 5V regulator is shot, with only a diode drop between Vin and 5V pin. Next question... is the whole Nano bad? When Nano's in the PCB, being supplied 9V to Vin, the 5V is at 8.3V, and I assume all the 5V parts on the Nano are getting 8.3V also.

Was thinking of replacing the regulator, but is it worth the effort if the entire board is suspect?

Try using it off USB only. If it works, it may well be all ok. Do some testing on downloading and IO.

It may simply be a faulty voltage regulator.

If it is a clone, they are so cheap you could just get a new one if there are any problems.

Weedpharma

If it is a clone,

No, genuine Gravitech Nano, $35. I should probably try a clone, but don't want to spent hours getting it to work right. Gravitech Nano worked first time.

It may simply be a faulty voltage regulator.

Probably is, but I wasn't doing anything unsafe when it happened. If it supplied 8.3V to everything on the Nano, its reliability is suspect.

The analog inputs look to be okay and it programs. Once regulator is replaced, probably just use it for testing and development as not sure I'd trust it.

If it rads 8.3 at 5V you need to test all the pins are working or not.
Do not connect the 9v and usb at same time, it may damage the USB on the PC.
Try the following to cheack if the pins can be turned high(+5v) or not

int i;
void setup() {
  for (i = 0; i <= 99; i++) {
    pinMode(i, OUTPUT);
  }
}
void loop() {
  for (i = 0; i <= 99; i++) {
    digitalWrite(i, HIGH);
  }
}

allPinsTest.ino (161 Bytes)

Thanks for the test code.

VUSB is protected from Vin by diode D.

Replaced the Nano's onboard 5V regulator and the board now appears to be working fine in my PCB. Since it was run for a while in the PCB with a faulty onboard regulator that was supplying 8.3V to the Nano's chips, probably wouldn't trust its reliability, but seems fine for development.