3v3 and output ports running at 4.6V on Photon

I am not sure what’s going on, but my multimeter is reading all of my digital output ports at 4.6V even the 3v3 port. Is there a problem with the built in regulator? My multimeter seems to be reading accurate values otherwise, So I don’t think it’s my multimeter.

I have a second photon and I measured the 3v3 output and it is 3.29V. So this one photon is behaving very strangely… I have it powered through the VIN with a TI LM1085 5V regulator. The regulator is currently plugged into a 12V power supply. When I power the device via USB, I get a similar output at the 3v3 pin… It’s slightly lower but still around 4.5V instead of around 3.3V

Oh man, sorry to hear that. I’m guessing it’s not running code properly anymore either? It’s possible the 12V to 5V pre-regulator was not regulating at some point and applied >5.5V to the VIN pin. If that should happen your 3.3V on-board regulator would be toast, and the STM32 would also be ready for butter and jelly.

The funny part is that everything is running fine. All code still executes. The IO pins are working, even the analog ports. I haven’t tested analog output, but input is working. I can still flash new code and everything. When I first unboxed it and was powering it via USB it failed to flash several times or the web ide reported a failure and it would flash seconds later. I haven’t seen that problem recently.

Very stupid question: You are measuring between 3V3 and the GND pin on the Photon itself?
And your Photon is out of circuit and USB powered? (avoid using the external regulator for testing this)

Sorry, but just to make sure :stuck_out_tongue_winking_eye:

Until this morning, I hadn’t taken it off the breadboard because everything was powered via the photon except the regulator. I still see the same 4.5V coming out of the 3v3 port when plugged into USB. I am currently measuring directly from a ground pin and the 3v3 pin with no breadboard.

What do you read on Vin when powered via USB?

It is very odd (but lucky) that your µC survives a 4.5V supply :confused:

via USB power I read 4.67 V at Vin

via 5V regulator I read 4.96V at Vin

Very odd indeed - but I wouldn’t tempt my luck and replace the onboard regulator.
But @BDub is the real guy there :blush:

Its very strange because I wouldn’t have normally taken the time to measure the 3v3 port voltage, but I had a transistor that was hooked up to a digital pin as an input pin with the internal 40kohm pulldown. The pin kept reading high so I started debugging my circuit. Turns out the transistor I was using that was powered via the 3v3 port was shorting. But I always had it hooked up to a 10 ohm resistor to make sure the digital port wasn’t driven with too much current. The collector read 4.6V and that scared me. I triple checked the rest of my circuits and the only place where more that 3.3V was supposed to be coming in was at Vin. My wiring check confirmed that.

As a side note the base of the transistor was hooked up to 3v3 with a voltage divider with several mega ohms of resistance on both sides, so at most I was seeing about 2.5V at the base (meaning the max current I could see would be even lower, I assumed the 40kohm internal pull down would be the primary influencer on the current at the digital port. while debugging this I found the 3v3 problem. I replaced the transistor and everything worked as expected. voltage at the digital input port was 1.6v and current was 0.03mA.

I think I found the regulator on the board, but I am not quite sure I have the dexterity to replace it! Any tips from any soldering pros? Also, where’s the cheapest source for me to buy a new one in the proper package. Mouser and others charge around $6 for shipping which makes me want to just throw away the board instead of replacing the regulator!

That is amazing!

If you measure the resistance from VIN to 3V3, what do you get? Should be several megohms until the input and output caps charge up a bit.

I had to leave for work, but when I test this in the evening, you want me to check the resistance when the device is not connected to any power source, correct? Or is there a gate that opens in the regulator when power is applied and with this open gate there will be several megaohms of resistance?

Measure with the power off, basically I’m trying to see if your regulator is shorted out from input to output. It could also just not be regulating correctly if the FB input is blown or open but that’s not as easy to test.

I just measured it. it is fluctuating but it is just under 9 megaohms

I have the exact same issue. Have you guys figured out what’s wrong?

In my case, I had hooked up an external voltage regulator that was overheating. Once it got too hot it triggered its internal thermal protection. This apparently caused a small AC current that apparently fried the built in voltage regulator on the Photon.