HMS 0300-0700-0001-0002: Motor-B short circuit
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HMS 0300-0700-0001-0002 means Motor-B is drawing more current than its winding resistance should allow. That is a short: two turns of the coil touching, or a winding shorted to the motor can. Unlike the open-circuit version of this code, a short usually is the motor, and replacing it is the fix.
Affected machines: A2L and P2S. Motor-B is one of the two CoreXY belt motors, so the machine stops rather than limps. The board shuts the axis down deliberately, because a shorted winding pulls current the driver cannot survive for long.
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How a short differs from an open circuit
Open circuit and short circuit sound like two versions of the same fault and are opposite problems. Open means the current cannot get through, and the break is nearly always a connector. Short means current is taking a path it should not, and the extra path is inside the motor where no amount of reseating will help.
That difference decides what you buy. For the open-circuit code, buy a meter and check the loom. For this one, expect to fit a motor, and use the meter to confirm the driver is not what failed.
Printer stops with Motor-B short circuit, sometimes after a period of stuttering motion
Shorted stepper winding, occasionally a failed driver on the board
- Power off at the wall and let the machine sit for a minute before opening it.
- Unplug Motor-B at the board and measure resistance across each coil pair at the motor.
- Compare the two pairs. Healthy coils read a few ohms and read the same as each other; a shorted coil reads noticeably lower than its twin.
- Measure from each pin to the motor body. Any reading at all there means the winding has shorted to the can and the motor is finished.
- Fit the replacement and set the pulley to the same height on the shaft as the original.
- Power up and run a homing cycle before starting a print, listening for an even sound from both motors.
If both coils measure healthy and the code still appears, the fault is on the board side. That is a driver failure, not a motor failure, and it is not a part you can swap at home on these machines.
The opposite fault on the same motor is Motor-B open circuit. Our page on CoreXY printers explains the belt path that makes both motors matter, and the troubleshooting index covers the rest.
HMS 0300-0700-0001-0002 FAQ
Can a shorted motor damage the board?
That is why the printer stops. The protection worked; running it repeatedly to see if it clears is what puts the driver at risk.
What reading confirms a short?
One coil pair reading clearly lower than the other, or any continuity between a coil pin and the motor body.
Could it be the cable instead?
A pinched cable can short two phases together. Inspect the loom where it flexes before you decide the motor is dead.
Is this the same motor part as Motor-A?
Yes on these machines, so one spare covers either position.
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