We made the board with the open source of Pocket Beagle.
We made a total of five.
Only one of them works, and four do not.
I don’t know the cause.
All pin maps have the same voltage.
The voltage of EMU0 (CDN of SD card connector) is 3.3V for normal board and 0V for abnormal board.
How to solve it?
What do we need to check?
I would start by having 3-D X-Ray of the solder balls under the main processor chip, to look for shorts, solder bridges and open ball connections.
Simple vertical X-ray will not always tell you what you need to know.
Are they resetting on power up? Reset button make them reset?
Is the oscillator oscillating?
What is the difference in power supply current between working and non working? Higher in non working might indicate short, solder bridge, too much flux.
Boot loaded programmed in?
On the PDF of the PocketBeagle-VDD power plane, only P1.14 and P2.23 appear to be connected, I could have missed the other connections. Again on the GND plane, only P1 and P2 connected. I guess the vias do not have thermals.
Has the PCB delaminated? http://www.surfacemountprocess.com/-pcb-delamination-during-reflow.html And broken the vias or tracks?