I use RPi B+ for playing a folder of videos automatically after boot. But the problem is that during the initial boot, the red LED on the board blinks 2 times (one after 4-5 seconds of boot, and the other after 5-6 seconds.)

I searched a lot on the net, and I'm pretty sure that the red LED on the board is related to power only.

First, I was using a cheap usb mobile charger; the red LED used to blink very often, both at boot, and later on operation time.

So I changed the PSU, and bought a reliable 5 V / 5 A power adapter!!

The number of the blinks of the red LED decreased. It was good. But still I would get blinks on the beginning of each video.

So I changed the power cables to thicker ones, because they can provide enough current.

Fortunately, the blinks on the beginning of each video disappeared, and it got solved.

However, still I get those 2 red LED blinks at the initial boot.

What would be the cause !!?

  • You say you changed to a reliable power supply. How do you know that it delivers what it says on the label have you actually measured the voltage on the board? Commented Jun 11, 2015 at 16:40

2 Answers 2


As you have already suspected, the red LED is blinking because voltage reaching Raspberry Pi's APX803 supervisor is below 4.63V. Good news is that it doesn't bother Pi much, if at all...

We're currently testing few Pis and one of them is connected to USB port on a very old Macbook that is supplying voltage of just under 5V (4,97V on average). USB cable connecting Macbook and Pi is very thin and Pi uses USB ports heavily, so the red LED on Raspi is blinking constantly for the last five months (Pi was off for maybe 48 hours in those five months)... But the Pi doesn't seem to care.

Raspi camera (which is connected to that Pi) took more than 1,5 million pictures, WiFi dongle still functions without a glitch and Pi is still in great shape. And it's slightly overclocked from day one (arm_freq=800, core_freq=300).

So, if you're annoyed by the red LED blinking, get a reliable power supply and USB cable or just stop paying attention to the blinking LED. :-)


Have a look at this link for troubleshooting.


  • Thanks @dastaan for the link. But I have already checked that page, without help.
    – Omid1989
    Commented Jun 11, 2015 at 12:34
  • Red LED is a power LED. Ideally it should not blink. Did you try changing Pi / SD card ? Also, which distro are you using ? Commented Jun 11, 2015 at 12:39
  • Yes, I changed the SD card, but it didn't help. I'm currently using Raspbian, but I had the same problem with Xbian as well.
    – Omid1989
    Commented Jun 11, 2015 at 12:48
  • @Omid1989 Did you change rpi ? Also, did you try powering it up via laptop / computer usb port ? Commented Jun 11, 2015 at 12:50
  • Changing the RPi is wiping out the problem, not solving it! And as I have described above, I used other power sources like usb chargers, etc. But they would cause more problems.
    – Omid1989
    Commented Jun 11, 2015 at 12:59

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