Did I kill my RPi 3B+?

So, I am embarrassed to post this. Are there diagnostics I can do on a Pi? I was booting up my Pi 3B+ with a 2 amp USB power supply (yes, not a 2.5 amp recommended by raspberrypi.org for the 3B+). I was getting the tell-tale lightning bolt in the corner, the command line complained about under-voltage. Did I take heed? Ummmm, no. But that may not be what caused my problem. Curiosity killed the cat. I wanted to know at what voltage the under=voltage message appeared. I poked around on pin 2 with my Fluke meter to monitor it. And, suddenly, everything shut down. Reboot didn’t cure it. Left it for an hour, still dead. It’s not a bad SD card (i’ve killed a few of those, different topic), because I had already converted the Pi 3B+ to USB boot, using a thumb drive with Raspbian. That thumb drive works fine in my other Pi 3. I get the red LED when I apply power, but nothing else happens.

Anything I can do to revive my Pi?

The Pi 3B only draws around 400mA bare board, nothing attached. A 3B+ may be a little more than that. Still not close to the 2.5 or 2.0 amp limit in your supply. The 2.5 Amp is “recommended” but not an absolute must be.

How did you prepare your SD card? There were some reports of false low volt indications after people did an update upgrade on their card to move it from an older Pi to a 3B+. The latest version of Raspbian fixes that.

Also, this is a low “voltage” warning not a not enough current warning. Although one can trigger the other. High current draw can cause the power supply voltage to drop under load. The other thing that can happen under high current draw is a voltage drop across the power cable. If it’s of poor quality with thin wires it will drop the voltage some. What did you have connected to the Pi? The low voltage warning trips at 4.65V at the PI.

All that aside, there is a poly fuse to protect against shorts. It is self healing but could take a while to do that. I’ve read that it could take days. So put that Pi aside for a few days and hope it recovers. If it doesn’t it, it is likely dead. If you just shorted the +5V to ground it may recover. If you sent +5V where it shouldn’t be, it likely won’t. Time will tell.

Thanks! That (might be) good news if it resets itself.

I am pretty sure it was an undervoltage event, during the boot up mixed in with the normal status messages, the Pi stated “under voltage”. Pretty clear to me. But it died while I was poking around with my voltmeter. I could have damaged a 3.3v circuit. . . .

Yeah, it will only ever display an undervolt (lightning bolt) or over temp (thermometer). My first 3B+ is on its way. I’ll likely get it in my hands early next week. If I’m really lucky today. Tracking stops when it crosses the big pond and reaches Canada, so I have no idea where it currently is.
I think what I would do while I’m waiting for it to maybe revive itself, is redo my Micro SD card with the latest Raspbian image, https://www.raspberrypi.org/downloads/raspbian/ 2018-04-18 is the latest that’s fully compatible with the 3B+.

Aaargh. I know I read this a while back, but this describes exactly what I (probably) did:

Be very careful with the 5 V pins P1-02 and P1-04, because if you short 5 V to any other P1 pin you may permanently damage your RasPi. Before probing P1, it is a good idea to strip short pieces of insulation off a wire and push them over the 5 V pins are not accidentally shorted with a probe.
I was probing with my voltmeter, unprotected.

I’ve let it set a few days, it’s not coming back to life. The “PWR” LED lights up when the microUSB power is plugged in, but the “ACT” light never, ever lights up. Maybe ebay wants a damaged Pi 3B+. :-(

Accidents happen. I killed 1 Pi Zero by plugging it in with only one row of GPIO pins connected to a pHat. It had a 90 degree header on it so not easy to notice. Power went where it shouldn’t. Didn’t hurt the pHat though.