I just loaded an SD Card with Raspbian lite for the Pi3 Model A+.

It does the normal rainbow screen splash, followed by the 4 raspberries and a blinking cursor underneath. The pi never completes its bootup.

The power led stays constant and bright.

The act led starts green solid, then blinks once, then it turns into a pinprick green led steadily flashing about once every second.

in the config file I do not have:


Does anybody have any ideas on what I can try or what may be wrong?

3 Answers 3


Okay - the problem was a silly one.

I just unzipped the raspbian lite img file and copy pasted the disk image.

I decided to reformat the sd, and use etcher to write the entire img file to the sd, and BOOM! It works!

  • Ah, what a happy ending.
    – tlfong01
    May 11, 2019 at 15:25

The pin-prick flash is the Pi trying to read the SD card. The Pi does this once or twice a second to see if an SD card is still inserted. It uses this method as the SD card present pin is not connected on the Pi. I presume this is used to detect if the SD card has been changed.


Update 2019may11hkt2325

I am sorry I have made too many stupid wild guesses in this answer. My explanation of the faint green led blinking is plain wrong, and suggestion to fix is ridiculously silly. Please ignore what I have said below. My apologies.


Rpi3A+ act led starts green solid, then blinks once,

then pinprick green steadily flashing about once every second


I googled and found the following forum discussion about the faint green led blinking once a second.

Disk activity led blinks once a second - rpi.org forum

The discussion ended with the following comments.

  1. The file config.txt might contain the statement "dtparam=act_led_trigger=heartbeat". Therefore green LED blinks once per second. It appears this statement is used to show that Rpi is working OK by hearti beating the green LED. If there is no such statement, then green LED blinks only when there is SD card read/write activity. In other words, just two methods of showing Rpi is still alive, and more or less working OK.

  2. If the "... trigger=heartbeat" statement is removed, or no such statement ever exists, but the green LED still faintly blinking, then the following is a possible reason:

    Something wrong with the hardware SD card detect line. The kernel therefore sends a "Send Status" command to the SD card once every 500ms or so. Getting a response means the card is still present. This activity is what is causing the faint blinking.

  3. So there is nothing serious to worry. It is just the SD detect line not working properly, and this causes kernel sending requests to SD card every half second, and SD card promptly responds, resulting the green LED blinking. The response is a very short pulse, therefore faint LED blinking. Everything except the SD detect line is working properly, and so this is not a serious thing to worry about.

  4. But if the boot process does not proceed further, I am afraid that there is not just the SD detect line out of order, the SD card might have other problems I don't know how to fix. :(. The last resort might be replacing the SD card reader, which is a SPI device and has only a couple of hardware wires interfacing. Or perhaps someone would google harder. :)

sd card interface

  • Ok -- thank you. The trigger=heartbeat line doesn't exist -- and the pi never gets past the 4 raspberries and blinking curser. So what's next to try? May 11, 2019 at 14:49
  • Ah, sorry, I have no idea how to fix.
    – tlfong01
    May 11, 2019 at 15:11
  • With your update: you may consider to delete the answer?
    – Ingo
    May 11, 2019 at 19:57

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