First time on the Raspberry Pi family, I just unboxed my Pi 3 model B with two successful boots after installing Raspbian.

Later I tried to boot again and I got a yellow flash symbol at the left side of the monitor during and after booting, and the power red led light keeps blinking. The mouse and keyboard are not responding, and there's no power on the USB port. I checked the ethernet port and no problem.

My power supply is 5V 2A. I also checked GPIO pins 2 and 6, and they are at 5.28V. Seems there is enough power but what could be the problem?

  • If the red LED blinks this means the voltage is dropping below 4.63±0.07V. Raspberry Pi Power Limitations. There may be something wrong with your meter, or an unusual level of ripple on the PSU. It is not difficult to measure the voltage/ripple with adequate test equipment. There is the possibility that something you have connected MAY be feeding power to the Pi.
    – Milliways
    Nov 12, 2016 at 6:10
  • What OS are you actually using. There used to be yellow and red squares appearing in the top-right corner of the screen, now there’s a lightning bolt for undervoltage, and a thermometer for overtemperature. I must admit I haven't actually seen them - I did make a rig to test undervoltage, but it involved some complex hardware to get it low enough to actually trigger.
    – Milliways
    Nov 12, 2016 at 6:17
  • I tried ubuntu core, raspbian and noob 2.0 still the same issue. I don't think the problem has anything to do with the OS.
    – ellooku
    Nov 15, 2016 at 5:04

1 Answer 1


The yellow flashing symbol typically indicates that the CPU is being throttled, possibly because of temperature. Do you have a heatsink?

See here for more info.

  • 2
    If the "yellow flash" refers to a lightning bolt, it is more likely to be the undervoltage warning; I think this is used now at least with the GUI and there's a thermometer for overheating. Undervoltage would also be in keeping with the red led flickering. The 5.28V test in the question may mean it is actually overvoltage, dunno if warns for that too...
    – goldilocks
    Nov 12, 2016 at 4:47
  • 1
    Search this page for "lightning bolt": raspberrypi.org/blog/introducing-pixel
    – goldilocks
    Nov 12, 2016 at 4:49
  • Everything worked at first but don't understand the issue now. I tried different AC adapters of rating 5V 2A but same problem. May be I should return it to the seller for another one.
    – ellooku
    Nov 12, 2016 at 5:33
  • 1
    @goldilocks If the red LED flickers, then it is definitely undervoltage. It is possible to turn the LED off with software (but this is involved, and unlikely to happen by chance). There is NO WAY the Pi can detect overvoltage.
    – Milliways
    Nov 12, 2016 at 6:03
  • Well, I returned it and got a working one. Thank you all for your input.
    – ellooku
    Nov 18, 2016 at 23:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.