STM32H407 LSE problem

[THEVENIN.CREALEAD]

Hello,

I use STM32H407 in a production environment, with no reliability problem except one.

On some boards, I cannot use the RTC with the LSE clock. I have looked with the debugger, and the software locks in the while(RCC_GetFlagStatus(RCC_FLAG_LSERDY) == RESET) loop
All happens as if the LSE could not start.

Is this problem known, is there a solution ? It looks like a hardware problem, sometimes it works when I put my finger new the 32768 Hz quartz.

[Lurch]

Maybe the crystal doesn't start to oscillate. This can be the case if the capacitance is way off or there are cold solder joints.  Not much you can do easily except check the solder joints.  Worst case, you can re-solder the parts or maybe replace the crystal.