STM32L496ZGT6P doesn't power on

[AndrewFFFF]

I assembled 2 boards (my design) with STM32L496ZGT6P.
I loaded the firmware..OK

The first board works fine

The second board sometimes doesn't power on. I checked the voltage (VDD).... is correct, but the microprocessor doesn't power on. It's a *** problem but i can't undestand why the microprocessor doesn't power on (sometimes) when Vdd is correct. Only fake contact or does anyone know some other reason for this kind of problem.

[KDJEM.1]

Hello @AndrewFFFF and welcome to the community :),

Probably, it is a soldering issue. 

Also, I recommend you to check your hardware implementation such as power supply. For that I advise you to refer to Getting started with STM32L4 Series and STM32L4+ Series hardware development  application note. This application note is intended for system designers who require a hardware implementation overview of the development board features such as power supply, clock management, reset control, boot mode settings and debug management.

Thank you.

Kaouthar

[SofLit]

As said by @KDJEM.1  refer to the hardware getting started.

Check the decoupling capacitors: did you mount all needed capacitors on VDDx?

Check your connections, MCU soldering etc .. 

[Tesla DeLorean]

No one here has any familiarity with your design beyond the scant detail you have provided. 

Are you sure it's not running? BOOT0 pulled low?

You got firmware onto the device, perhaps it is stuck in a while() loop in the Error or Hard Fault Handler ?

[AndrewFFFF]

Thank you for the answers.

I share some screenshots from my board.

After the power on, the board power on the buzzer and the display...but sometimes is all off and Vdd is 3.3V.

I'll check again the soldering issue.