This is what happened: I ordered a Pi 4B a few months ago, but never used it since I still had a Pi Zero running. On powering it up, the Pi 4B wont start.

  • I am using the HDMI0 output
  • The SD Card should be a high quality one (some new ordered Samsung) as it works with my Pi Zero
  • On the card is the newest version of the Raspberry Pi OS, installed with the Raspberry Pi Imager
  • The Power Supply is the one that was recommended by the retailer, so this should be fine

This is what happens:

  • The red LED shines the whole time the Pi is powered
  • The green LED (labeled act, if I am correct) blinks once and that´s it

I do not think, that any of these Flashlight Codes are applicable since there is no long blink. Also this guide didn´t help me either.

The Pi is connected through a Micro HDMI to HDMI adapter and then through a HDMI cable to my monitor. Again this works just fine with the Pi Zero. I couldn´t test the Micro HDMI adapter, but I ordered a new one with the Pi 4B and I had an old one lying around and neither of those work.

This is all the information I got, I hope some of you can help me.


  • what happens if you power up the RPi without an SD card? ... same for the HDMI cable ... basically, make changes to the setup in an effort to get different behavior from the RPi
    – jsotola
    Commented Sep 5, 2020 at 18:40
  • See Pi4 Boot Problems Sticky
    – Milliways
    Commented Sep 6, 2020 at 1:17
  • I already followed the Pi4 Boot Problems sticky guide, but thanks. I tried powering the Pi in every setup i can imagine. Still, everytime its the same outcome. The red LED goes on, the green blinks shortly one time. I also tried to recover the bootloader with the Pi Imager, but still the same result.
    – Appa
    Commented Sep 6, 2020 at 8:00

1 Answer 1


If nothing helps, even the Pi4 Boot Problems Sticky, then you can have a look at the debug output of the bootloader at a very early stage. For this you need a cheep USB to TTL serial adapter. Google for it and you will find some sources where you can purchase one.

Then connect the USB to TTL serial adapter and enable debug output of the bootloader as shown at Serial output in case of no OS.


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