HMS 0300-0700-0001-0003: abnormal Motor-B resistance
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HMS 0300-0700-0001-0003 means Motor-B is measuring outside the resistance the firmware expects. This is the third of the three Motor-B codes and the most specific: the circuit is complete, so the wiring is doing its job, but the winding itself is not what it should be. That almost always means the motor.
Affected machines: A2L and P2S. Motor-B is the right-hand motor of the CoreXY pair. A resistance fault does not stop the axis in the way an open circuit does, so you may see stuttering or lost steps before the printer gives up and reports it.
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What the three Motor-B codes actually mean
They are not three severities of one problem. An open circuit means current cannot get through, and a connector explains it. A short circuit means current is finding a path it should not, and the winding explains it. Abnormal resistance is the middle case: the path exists, the current flows, and the number is wrong.
The practical value of that distinction is where you look first. For this code, do not spend an hour reseating connectors. Measure the motor, compare it with its twin, and let the numbers decide.
Stuttering motion, occasional lost steps, or the printer stopping with abnormal Motor-B resistance
Partially failed stepper winding, occasionally a marginal high-resistance connector
- Power off at the wall and let the machine reach room temperature before measuring.
- Unplug Motor-B and measure resistance across both coil pairs at the motor.
- Compare the two pairs on that motor. More than a fraction of an ohm between them points at the winding.
- Compare Motor-B with Motor-A, which is the same part. The odd one out is the faulty one.
- Check each pin against the motor body. Any continuity there means a winding has shorted to the can.
- Fit the replacement, set the pulley to the original height on the shaft, and re-run a homing cycle before printing.
Measure cold. Copper resistance climbs with temperature, so a motor tested straight after a long print can read high enough to look faulty when it is perfectly healthy. Half an hour off is enough.
The other two faults on this motor are Motor-B open circuit and Motor-B short circuit. Our page on CoreXY printers explains why one motor affects both axes, and the troubleshooting index covers the rest.
HMS 0300-0700-0001-0003 FAQ
What resistance should Motor-B read?
A few ohms per coil pair, with both pairs matching each other. The match matters more than the absolute figure.
Can a cable cause this code?
Rarely. A high-resistance crimp can add enough to shift the reading, so inspect the connector before you condemn the motor.
Is Motor-B the same part as Motor-A?
On these machines, yes. That is what makes the side-by-side comparison so useful.
Can I keep printing until the part arrives?
Not safely. A winding that is already out of spec will get worse under load, and lost steps mid-print can drive the head into the part.
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