I have a Pi 3B+ that wont boot. It's a "new" unit that I received as a gift a few years ago and am just now taking it out of the box and trying to use it.

I've tried several OS images, but they all behave the same way... a rainbow screen with a yellow lighting bolt in the upper-right corner. The power LED flashes slow4 times and then fast 4 times.

From what I've gathered, this indicates that the firmware needs to be updated. But, I can't get an OS to boot in order to update the firmware. All of the articles I have found talk about updating the firmware on an already working OS image. I can't even get that far!

How do I update the firmware if I can't get an OS to boot at all?

  • Get a brand new 32GB SDCard. Download the Raspberry Pi Imager from raspberrypi.org/software (your laptop needs an SDXC reader to use that). Run the imager (it will automagically download RaspiOS for you), let the Imager verify that the SDCard has been written OK. Stick the SDCard in your RPi and power it up. The RaspiOS written with the imager will get the right "firmware" loaded on your new SDCard.
    – Dougie
    Commented May 14, 2021 at 11:12

1 Answer 1


Ugh. What a misleading error code.

The problem was with the SD card I was using. I don't know why..., that card worked in every other rpi that I have, but not the 3B+. Changing to a different card allowed the system to boot right up.

I saw lots of articles about the flashing red light sequence and how it indicated a problem with the firmware or the power supply... nothing that I saw pointed me to the SD card.

Anyway... I hope this helps someone else.

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