I'm having an issue with my Pi 3 regarding power/heat issues.
I have a setup where a UBEC has been powering a Raspberry Pi 3, 5in HDMI touchscreen, and small fan for a project. It was running fine with temperatures measured from
vcgenmd measure_temp being less than 70 .
Recently, the Pi would not boot even though the UBEC was still giving power to the screen. I opened the case it was in, and plugged power into the UBEC again. I thought I saw a faint curl of smoke and smelled a faint burning smell but I inspected the Pi and UBEC and they all looked good.
I booted the Pi 3 again without the extra screen and case and used it for 2 or 3 hours using a 5v 2A power supply I had. It worked fine but there was a solid rainbow square in the corner so I decided to power the Pi with the UBEC again over the GPIO like in the previous setup.
I did this and the Pi booted, but after about ten minutes it started rebooting continuously and the UBEC light flickered of and on. I tried powering a Pi 2 and Pi B+ with the same UBEC and it worked perfectly. The UBEC is rated at 5V/3A and 5A max. I tried different cards with different OS's that I knew worked in the other models and the Pi 3 would sometimes boot but always start rebooting after max 10 mins.
At one point it would not boot being powered with 5V/2A supply or the UBEC. I let it alone for an hour and then it would boot again, but I had the same problem after a couple of minutes.
All I can think of is some fuse on the Pi, that won't let it boot if its too hot and I should just wait a day or two before using it again? Any ideas what might be the problem? Thank you in advance.