My CTC printer was working fine the first few days. Had to move it to another room and while doing so the print head slid to one side along the linear guide. A few days later I was showing it to a friend and absent mindedly pushed the print head to the side a few inches. The display screen immediately but briefly powered up despite the fact that the printer was not plugged into an outlet at the time. My best guess is that back EMF From the movement of the print head has some how damaged the printer. It powers up but does nothing else. The manufacturer wanted me to pay for postage on the replacement board. I ended up ordering on off Ebay for $40.00 I will let you know how it works out.
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Back EMF is a thing, yes.
So far I’ve not had any bad things happen from moving the axis by hand, but a different mainboard might be less robust.
I hope its not a geetech board. You will need a different power supply as it lacks the 5v regulator. It comes with incompatible drivers, the standard drv8825’s which are a different pinout then the botsteps. as well as few other issues. ebay is generally the worst place to get replacement parts. My CTC printers has a flashforge motherboard.
I’ve never had any issues from doing this on my stock geeetech prusa i3, but theoretically you could cause damage to the stepper drivers.
My CTC screen lights up when ever I move the head as well but it’s never caused damages
Iv done it plenty of times
Yeah, I’ve always found that a little disconcerting… (You’d think there’d be some manner of protection designed into the board or the stepper drivers…) But I have yet to damage my printer that way. :S
Suggy
7
Would it be possible to put diodes in the motor wires?
The stepper drivers have built-in diodes already for exactly this reason. Thats why the lights went on when you moved the motor, the generated power was rectified and put on the 12V connection. If they didn’t have diodes, the drivers would’ve fried instead.
Why your mainboard fried because of it, I don’t know.
If there are diodes in place, wouldn’t they interfere with voltage reversals during normal operations? A single diode would prevent the motors from reversing. A half wave rectifier would allow the voltage to back feed offering no protection.
No, they don’t conduct, the diodes are not across the motor, but from the motor to the supply rails.
The diodes are connected anti-parallel to the mosfets inside the driver (forming a full bridge rectifier), they don’t conduct during normal operation, as their forward direction is always connected to a higher voltage, but they would conduct if the motor is generating more back-EMF than the supply rail voltage.
Any motor driver, in fact (almost) every mosfet, has these diodes. 
