I'm still not sure what happened, but I seem to have fried my Arduino Giga, as the mysterious blue smoke started coming out of the L1 inductor by the 5V pin when I connected it to the USB-C to power it on. Now, I have continuity between the 5V and ground pins, and it looks like I need to order a new board.
I am wondering if I need to buy a new Giga Display while I am at it though. Is there a way to test to see if the Display is also shot? I did try connecting it to a 5V power supply, but nothing happened (e.g., no backlight).
I would suggest just replacing both as you do not know what is damaged.
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If you're wondering what happened when the board fried, here are the details.
I connected the VIN pin and ground to a 12VDC buck converter, and the green LED on the back came on and the Display backlight turned on, but nothing loaded.
I disconnected it from the power and connected it to a USB-C, and everything loaded fine.
I had previously ran the board on 24VDC using the VIN pin, so I tried that again with a dedicated power supply, and the green LED and Display backlight came on but nothing loaded.
I disconnected it from the 24VDC power, but I didn't remove the jumper wires from the VIN pin (though they couldn't short because they were connected to an adapter for the disconnected power supply), and I connected it to the USB C. After a second or two, the inductor started pouring out a big cloud of smoke and I disconnected it immediately.
I also noticed that three of the four solder points in the USB-A and one of the USB-C shells on the back of the board looked like they had melted and blown out (though there was no sign of solder splatter on the back of the Display, but I don't remember if I checked this when I first got it) and one USB-C solder point was completely missing solder. I'm writing this in my phone, so I am hoping that the picture uploads.
Hi, @littlejohn657
What is your 24V supply?
Do you have a fuse in the line or can you current limit it?
Thanks.. Tom.... 
I figured out why the display wasn't loading with the VIN pin. The serial monitor was turned on in the code, so it was waiting to connect. It loaded on my computer though because I had the Arduino IDE open for another project that I was working on and forgot was open.
I have a 24VDC 6A power supply, but I am running quite a few components so I have a 5A fuse. The reason that the display wasn't turning on was because the Serial monitor was set to on in the code and it was waiting for that to connect (impossible on the VIN power).
I don't have a specific fuse though on the USB power though, as that is regulated in the computer, and it was connected to the computer and not 24VDC when it fried.
Hi,
Measure or calculate what the current consumption will be of your project at 24V and fit a fuse that is rated just above that.
By the description of your project, current consumption at 24V would have been 100s of mA.
A short with 5A fuse would mean you had 5A or more flowing through your project, that can do, as you have found out, quite a bit of damage.
You need to fit a 1A or 500mA fuse.
Do not use Automotive fuses, they can take up to twice or more of their rated current to blow as quickly as needed with an electronic circuit.
Tom....
When it fried though, it was running 5V on a USB C, and no peripherals were attached other than the display—no sensors, no motor, nothing. I don't know how to install a fuse in a USB-C, though I am not sure that one is needed or would have saved me here.
Yes, and I am looking into setting that up. It wouldn't have helped me this time though.
