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3D Print Troubleshooting, Calibration & Parts

HMS 0300-2000-0001-0004: Y axis homing failed, timing belt loose

By LayerWalkerUpdated September 17, 20263 min read
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HMS 0300-2000-0001-0004: a loose belt shows as ringing while printing but makes the homing position unrepeatable, and pulley grub screws should also be checked.
Short answer

The firmware attributes the homing failure to belt tension. A slack belt lets the carriage lag behind the motor, so the machine cannot trust where the axis is. Tension it, then re-run calibration.

Difficulty easy Time 20-40 min Parts none to under $20 Tools Hex keys, cloth

Affected machines: A2L, P2S, X1 series. Homing is the machine establishing where the axis actually is, so a homing failure stops everything downstream of it.

Judging belt tension by ear: a dull thud is too loose, a clear note is about right, and a high ping with a stiff axis is too tight.
Belt tension has a window, not a maximum. Too tight loads the bearings and wears the rail, so the target is a clear note rather than the tightest you can manage.

Where to buy

Why slack breaks homing rather than just quality

A slightly loose belt usually shows up as ringing on a print. Homing is stricter: the machine drives the axis until it detects the end, then uses that as the origin for everything afterwards. If the carriage lags behind the motor by a variable amount, the detected position is not repeatable and the firmware rejects it.

That is why this code can appear on a machine that was printing acceptably the day before. The tolerance for homing is tighter than the tolerance for looking fine.

Symptom

Homing fails, or the axis reaches home but the machine reports the position as implausible

Most likely cause

Timing belt has relaxed, an idler has loosened, or a pulley grub screw has backed off

The fix
  1. Power off at the wall and clear the plate.
  2. Pluck the Y belt like a guitar string. A correctly tensioned belt gives a clear note; a dull thud means it has relaxed.
  3. Check the tensioner and the idler for a fastener that has worked loose.
  4. Check the grub screws on the motor pulley. A pulley slipping on the shaft mimics a loose belt exactly and is fixed differently.
  5. Adjust tension so the note is clear, without going tight enough to make the axis hard to move by hand.
  6. Home the axis, then re-run the resonance calibration so the stored baseline matches the new tension.

Our page on belt tension covers judging tension by ear and the real failure mode of over-tightening. Lubrication covers what belongs on rails and what must stay dry, and the troubleshooting index covers the wider family.

FAQ

Can I home by hand first? Moving the head gently by hand to feel for a tight spot is a useful diagnostic. Do it with the power off.

Should I tighten the belt until it is very tight? No. Over-tension loads the bearings and shortens their life.

Why does it only fail sometimes? Marginal tension or a tight spot at one end of travel produces exactly that pattern.

Does the print need to be removed first? Yes, if anything is on the plate that the head could strike during homing.

LayerWalker

Print defect diagnosis, calibration procedures and parts that actually fit. Corrections welcome through the contact page.

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