HMS 0300-0100-0001-000A: heatbed control abnormal, AC board suspect
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HMS 0300-0100-0001-000A means the printer cannot control the bed heater properly and suspects the AC board. This is the mains side of the machine, not the low-voltage sensor side, which changes what you should and should not do about it. The bed may still heat, heat slowly, or overshoot.
Affected machines: A2L and the X1 series. The AC board is the component that switches mains power into the bed heater. It sits behind its own cover for good reason, and nothing on it is a user-replaceable part.
Where to buy
What you can safely establish yourself
Two things, both with the machine unplugged. First, that the bed thermistor is healthy: unplug it and measure across the pins cold, where a working sensor reads around 100k ohm. Second, that its connector and lead are intact along the run to the board.
If the thermistor is fine and the connection is sound, you have ruled out the cheap half of the problem, and what remains is the control side. At that point the answer is a service ticket rather than a screwdriver, because everything left is at mains potential.
Bed heats slowly, overshoots, or the printer stops with a heatbed control fault
Failed AC control board, occasionally a bad thermistor or connection
- Unplug the printer at the wall. Do not work on this fault with the machine powered, even at the display.
- Wait several minutes before opening any panel, so that mains-side capacitors have time to discharge.
- Unplug the bed thermistor and measure across it cold. Around 100k ohm is healthy; open or near zero is the fault.
- Inspect the thermistor lead along its run for chafing where it flexes with the bed.
- If the sensor and its lead are healthy, stop. Record the code and raise a support ticket rather than opening the AC board cover.
If the machine is out of warranty and the board is confirmed dead, the arithmetic is uncomfortable but simple: a service board plus labour approaches the price of a current machine, which is why the last bar on the chart above is there.
The sensor-side fault on the same bed is heatbed sensor open circuit, which is a genuine home repair. Our page on bed temperature explains what the sensor controls, and the troubleshooting index covers the rest.
HMS 0300-0100-0001-000A FAQ
Can I keep printing PLA with this code?
Do not. A bed heater that is not under proper control is the one failure mode on a printer with a real fire risk.
Is the AC board the same as the mainboard?
No. The mainboard runs the printer at low voltage; the AC board switches mains into the bed heater.
What should the bed thermistor read?
Around 100k ohm at room temperature, falling as it warms.
Is this covered by warranty?
It normally is while the machine is in warranty, and it is the sort of fault worth claiming rather than attempting.
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