I have a Raspberry Pi 3 Model B+. When I turn it on, it works fine but the red PWR LED keeps blinking. Everything else works fine, with no issues, but when I power it off and turn it on again, then it works fine—the red LED stays on and the Pi works fine.
Why is this happening, and how can I fix it?
This might be a power supply that is just barely good enough. The APX803 gets triggered the first time, but not the second time. Probably a power supply that is just around the threshold.
Red power LED is blinking
...
On model B+ (and presumably also the A+), the circuit has been improved to give a much more reliable warning of poor power quality. The red power LED is wired to an APX803 supervisor[2] which kicks in when the 5V power supply drops below 4.63V[3]. If it does, the LED will blink. Check your connections, cable, and power supply.
