I have a strange problem with a Pi 4.

I have my Raspberry Pi 4 powered by an external alimentation 5V 2 A, there are two USB devices connected (an Arduino Mega and the touch USB for the display) and an HDMI display.

When I am trying to boot from an SD card with this configuration, it won't boot. But when I unplug a USB device it boots. I can then reconnect the USB device and it works perfectly.

I don't think it is a power supply issue because it works after I unplug and plug again...

Does someone know why this happens?

  • I don't know if it's still true for the Pi 4, but earlier versions had weakly powered USB ports. If your devices are trying to pull too much current there, you could have issues. A powered USB hub is the usually recommended approach to this ailment.
    – Brick
    Sep 13, 2019 at 16:16
  • 2
    The PSU is marginal (on the edge) for a Pi 4. If the connected USB devices each take a surge of power at startup, at the same moment that the PI is starting, that can drag the PSU voltage down so that the Pi will not boot. The PSU voltage would then rise again, but it's too late for the Pi, which remains unbooted. Disconnecting one of the USB devices before boot would reduce the sag, and allow the Pi to boot. Sep 14, 2019 at 8:28
  • I have the same problem, but the usb thing plugged into the usb port on the pi4 is powered, and has a 3amp supply, so it's not a power issue.
    – stu
    Mar 1, 2020 at 14:02

1 Answer 1


It is very likely a power supply problem. As you can see at Raspberry Pi 4B specifications you need to have:

  • 5V DC via USB-C connector (minimum 3A*)
  • 5V DC via GPIO header (minimum 3A*)

* A good quality 2.5A power supply can be used if downstream USB peripherals consume less than 500mA in total.

You only use a 2A power supply and this must also power two additional devices. This is not enough in any way.

  • Thank you for your response. But After some test we tried to put a power supply with 3 Amp and there is still the issue. We put a 11 Amp power supply and still the issue ... So we don't think this is the problem.
    – Buisson
    Sep 20, 2019 at 12:43
  • @Buisson So it must be a problem of the USB device and of the Raspberry Pi.
    – Ingo
    Sep 20, 2019 at 16:46

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