Suspicious voltmeter checks

I just blew the voltage regulator on a photon - not sure how it happened, but the component burnt and bubbled, and would only power up when given 3.3v into its 3v3 pin. Darn, must have been careless. Guess this one is done for. I tore it out, examined the circuit, cleaned up some potential shorts, and stuck in a new Photon.

Gotta be careful this time - Before even touching the power supply, I got out the voltmeter and found no resistance between ground and 3v3. Rats. After increasingly desperate examination of the setup, I now have the 3v3 pin and the Vin pin totally isolated from the circuit, and there’s STILL no resistance (~1 Ohm) between either of these pins and ground. I’m assuming this should not be the case for an out-of-the-box photon which has yet to be powered, but I’ve been wrong before. Is this normal? Should I try to power it? Or have I found a defective unit? The regulator looks fine (unlike the other one which is clearly fried).

Are you measuring with the Photon placed onto your circuit or removed from the setup you have?

All Photons are tested and verified to be working before it leaves the factory so the chances of it having a short upon unboxing is minimal. Not saying it won’t happen but the chances are fairly slim.

The photon is currently soldered to my perfboard, but I’ve removed all connections to the Vin and 3v3 pins (by cutting traces so that they touch only a single pad of my board).

I agree that this seems an unlikely problem to encounter with a new Photon. The only possible things I can think to have caused this are a capacitor discharge (though the largest capacitor in my circuit is 1uF), or the current from my multimeter (I did notice the continuity check function supplied enough current to dimly light up the RGB LED). Both of these seem unlikely.

Just to check: Am I correct in assuming that measuring zero resistance between Vin and ground indicates a problem? I still have yet to try powering Vin.

Since my last post I did try (very carefully) putting in 3.3V to the 3v3 pin with a digital power supply, and the photon began booting up, though the regulator felt a bit warmer than usual. If anyone has any insights into what might be going on I’d greatly appreciate it.

I’d say the method and/or the DMM you are using to measure the “resistance” between 3V3 and GND is causing the confusion.

You should definetly not see low resistance (couple of Ohm) between these pins, but depending on your DMM and selected Ohm range, you might see the caps charging up or if you change polarity while the caps are charged, you might even see negative resistance.