I have several hundreds of PCB with this circuit, and they work fine. However recently I have had a few of these PCBs stop functioning. I have tracked the problem to diode D1.
When applying 12V to the input I have measured 1.8V on the cathode of the diode, and no appreciable input current (the power supply shows 0.000W output power), so I have discarded a short-circuit down the line as a possibility.
Now comes the interesting part. I tried slowly increasing the voltage to see if there would be any change on the output current. To my surprise, the diode started conducting at around 16V, and when I measured the voltage drop across the diode it was back to its normal 0.7v to 0.8V. After this the PCB was functioning normally again, and I was not able to reproduce the behavior. As matter of fact, now when applying a 12V input, it works as intended.
I have seen this behavior on at least 3 or 4 PCBs out several hundreds identical PCBs.
I am assuming this is a defective diode, but it is the first time I observe this mode of failure and I would like to get more information about it.
EDIT: I would like to add that I made sure that the connector and cable were not at fault here. Also the measurements are on the pins of the diode itself. Furthermore, when increasing the voltage on the power supply, I made sure I was not touching any of the cables or PCB because I suspected that could be one of the problems, but it is not apparently.