I replaced the stm32f407ve chip on my board but it didn't work

[duong]

on my mks monster8 v2 3d printer control board using stm32f407ve chip it was damaged specifically gnd pin and vcc pin are connected, i bought another chip and soldered it to the board, however when plugging in usb it does not recognize com port, i tried connecting with my stlink v2 it still displays the necessary parameters and can read and write, i loaded blink led program and it works however when loading printer firmware specifically marlin it does not work and usb connected to computer does not recognize com port

[SofLit]

Hello @duong and welcome to the community;

As you have replaced the MCU, double check the hardware, mainly the USB part.

[duong]

I checked the hardware again, the two pins d+ and d- of the usb are connected directly to the microcontroller through the two corresponding pins PA12 PA11, it is soldered exactly according to the pin out of the board manufacturer

[Tesla DeLorean · Accepted solution]

The failure is perhaps more involved. You'll need to get a schematic and work through the circuit. You've likely damaged the supply, check voltages and components in the path.

Perhaps find a repair technician familiar with the board, or find forums dedicated to support of the board,

[duong]

maybe you are right, i measured the resistance on pin pa12 with gnd, the value is 6.5 ohm and pa11 with gnd, the resistance is up to Mohm

[duong]

pa12 is 6.5 kohm

[duong]

i replaced a new chip loaded the program with st link and tried with the code the led blinking works fine but still can not connect to usb, i hold boot 0 and power on bootloader mode still works, did i forget some step, please help me