Failed first time boot of DB820c

I am try to boot my DragonBoard 820c for the first time, following instructions in “Getting Started”. I connected the board to HDMI display, USB mouse and USB keyboard, had make sure the boot switch was set to “0000”, and plugged in the power, but there is no HDMI output. The power indicator LED is on, and User LED 0 is blinking, plus the BT LED is on.

Is there really a default OS onboard? How can I check it? Or how can I check if there is a hardware failure?

Hook up UART to see what it does.

It boots after I pushed the boot switch hard. Maybe the default position of that switch seems to be “0000”, but not.

With switches to all off, it should boot automatically.

I mean there might be poor contact in the switch. It works after I pushed and pulled the switch.

I doubt that. If a switch like that has bad contacts, it would typically act off when it is switched on. Since you have them switched off, the typical failure mode would not be evident.

Since the pins of that switch are accessible, I suggest confirming by checking for continuity across the switches.

Is it possible that you just didn’t wait long enough for it to boot, and that after the time you spent poking the switch it got to where you were expecting?

Also note that you absolutely should NOT be changing those switches with the power on.

I think the time should be long enough. I powered it on and went for lunch.

I was toggling the switch with the power off. I was trying to use SD recovery, but failed. After switched back, everything went fine magically.

I just remembered something. Bootup was extremely unreliable with the more recent builds of kernel 4.x. If your board has that preinstalled, then you may experience successful boot about 25% of the time. The newer builds use kernel 5.x and boot reliably. Check what kernel version yours has installed and upgrade.