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bigtreetech / BIGTREETECH-S42B-V1.0

The closed-loop drive is to feedback the rotation angle of the stepping motor to the control panel, compare the distance that needs to be rotated with the distance of the actual rotation, calculate the error value, and then compensate, so as to prevent the problem of multi-step and lost step. The closed-loop drive can completely overcome the lost step of the open-loop stepping motor, and can also significantly improve the performance of the motor at high speed
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Board no longer powers up #28

Open MetalBeard72 opened 3 years ago

MetalBeard72 commented 3 years ago

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 commented 3 years ago

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 commented 3 years ago

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 commented 3 years ago

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 commented 3 years ago

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. image