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Heart transplant

A project log for CoreXY pen plotter

Created using FreeCAD and Zephyr RTOS. Inspired by AxiDraw.

lukasz.iwaszkiewiczlukasz.iwaszkiewicz 5 days ago0 Comments

As I have written yesterday I want to switch from STM32F446RE to STM32405RG because it has more flash and I happen to have a few of them (soldered to variety of prototypes, state unknown). The STM Cube MX reported that the two mcus are pin compatible - at least I understood it that way :

So the only thing to do was to replace the MCU on my nucleo_f446re board, since I do not have any PCB designed yet, and I use the  nucleo for prototyping. Easy! Without even disconnecting the cables (power was cut off of course) I secured other components from heat:

I flushed pins with leaded solder to lower the melting point. Not necessary:

Heated everything up:

And voila! No heart in this patient any more:

Next, using the soldering iron I fixed new (de-soldered) chip in place:

The whole operation took me like 45 minutes, but to my disappointment the board didn't work any more! I'll skip the story of trying 5 consecutive MCUs in a row, suspecting that they are broken. They all have been de-soldered from scrapped (and old) prototypes after all.

Then I compared the pinouts, but this time looked into datasheets. And no, the pinouts are not the same!

TL;DR : pay attention to pins 30-31 and 47 (LQFP 64). In my case I had to remove jumpers SB33 and SB38, and solder C22 and C25.

And at the end:

Finally...

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