Board no longer powers up

[MetalBeard72]

I'm afraid I fried my board. I have been very careful to power down before making any connection or switch changes. Now the green LED no longer turns on. Just on the off chance that I can resurrect this thing, Has anyone else saved one of these?

[Quas7]

can you still communicate with the controller via the SWD interface (e.g. still program it?), if powered only via the SWD interface?
If this does not work anymore, I would trash it.

[Quas7]

Maybe also check with magnification that there is no bent pin/short or any other metal flicker sticking somewhere.
Reassembling the boards often might have thown some metal splinters from the screwing process on the board...

[dzid26]

I wonder if BEMF could have kill it.

Because when I drive the motor from the output fast enough, the MCU resets. @Quas7 Do you have idea why is it restarting?

The input voltage is stable and current is never reversed. - Hmm, maybe that's the key, because I think the board have reverse polarity protection diode. So if that diode doesn't allow the current to flow in reverse, the internal voltage will rise high. Though, I would expect the linear regulator to heatup, and no MCU reset.

....Hah, while writing this I run it with a drill for a bit longer, while it was reseting. It seems the A4950 didn't handle BEMF. Mosfet are shorted and it is drawing 0.4A continuously now. Bummer.
But MCU still works.

Anyway, I still don't udnerstand why it was resetting.

I guess for now I am going to stick with MKS42B which doesn't have reverse polarity diode. I also put clamping diode on supply lines to protect for overvoltage.

[dzid26]

The damage was due to lack of protection against BEMF and reverse polarity protection not allowing to sink current back to power supply.
@bigtreetech V2.1 could be improved.
I added clamp (18V unidirectional TVS) diode between A4950 VBB supply and ground. That fixed resets when backdriving and now the board is safe.