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NEO4 stuck in boot cycle

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Hello guys,

I have two NEO 4 boards with heatsinks. Unfortunately both of them are stuck in boot cycle. When I connect power, they briefly show FriendlyElec logo on screen and then again and again. I am using sd card with rk3399-sd-friendlycore-bionic-4.4-arm64-20191227.img image. Via console on usb to serial there is no output.

here is the video: https://photos.app.goo.gl/w1HamDjzCEdEen9b8

do you think they are burned or can I do some deeper debugging?

thanks in advance
Best way is to connect to the debug port and look at the boot output. This will tell you what is going wrong.
Thanks that is exactly what I did. Without HDMI cable connected I am getting gibberish output on serial as shown on attached image. My serial settings are (same settings work fine with for example nanopi core2):

speed: 115200
Data bits: 8
Stop bits: 1
Parity: None

Funnily board seems to be coming up, I have also green led blinking of reading from sd card. Do you know any other settings?


Gibberish usually indicates a missing ground connection.

ok now I am completely baffled. After finishing the boot on serial with gibberish, I have connected HDMI cable and I get the image. Just for information I have serial 2 USB cable from Adafruit with CP2102. I am going to test second board.


v8dave wrote:
Gibberish usually indicates a missing ground connection.

it happens with or without ground
It all sounds like a ground issue. I assume you are using a 3.3V TTL serial interface to connect to the debug port?
yes it is 3.3V USB to TTL cable from Adafruit. Specs are here:

When you connect to the board, do you just connect GND, RX and TX?

You don't need the 5V connection as your board is powered elsewhere. Better to leave this disconnected to avoid shorting power supplies.
Hi v8dave,

sorry for not replying I've been busy on other project. Today I had a chance to retest everything. As for your question, yes I did not connect 5V it was only RX,TX and GND. Conclusion is:

not compatible USB-C power supply

I have connected to USB-C psu of my laptop and it was same stuff (rebooting), then I disconnected USB-C power and connected only on USB to TTL cable. Suddenly whole thing boots. Then I've got another USB-C psu brick from my phone and voila it worked like a charm. I've tested all important functions like wifi, video playback and so on, all seems to be working.

NOTE: however serial debug output stays garbled (something must of been damaged) but board as such works and boots ok.

For convenience I have attached dmesg output, if you would see something suspicious there.

In any case thanks for patience and help. Have a nice day.


Everything looks good in the output.

I see you are running Android on this.

If you have a PC running Ubuntu, it is quite easy to build your own custom OS and get rid of the stuff you don't need. All depends on what you are wanting to use it for.

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