Board, cables and sensors: what to check before replacing the board

When the printer shows a temperature error, can’t detect filament or suddenly restarts, the board is the first thing that comes to mind. In reality the culprit is usually a loose connector, dust in a sensor or a frayed cable — and you can check all that in half an hour at no cost.

Safety first

Bambu Lab stresses this specifically: before any work on the electronics and the print head wiring, turn the printer off and unplug it. If you take the head apart with the printer on, exposed contacts can short against each other or against metal — and then electronics that were working get damaged too.

The bed is heated directly by mains voltage, so anything involving the bed or the power board is done only with the printer unplugged.

The printer “can’t see” the filament

Signs of a faulty filament sensor in the print head, according to the manufacturer:

• the message «Failed to send filament to the extruder», even though there is filament in the tube above the head;
• when printing with the AMS, the printer asks you to pull the filament from the external spool even though the tube is empty;
• the printer asks you to push the filament all the way in even though it’s already in the extruder.

How to check

1. Press the black part of the connector and pull the PTFE tube out of the head inlet.
2. Insert a piece of filament into the inlet.
3. Look at the printer screen: a small green dot should light up next to the extruder.

If the dot lights up when you insert the filament, the sensor works. If it doesn’t light up at all or stays on all the time, keep looking.

What to do

1. Turn the printer off, remove the sensor housing cover and flip open the Hall sensor board.
2. Blow out the area around the magnet with air or a hair dryer — most often filament dust jams the magnet.
3. Insert a piece of filament and make sure the magnet moves freely.
4. Wipe both sides of the board with a clean paper towel, reassemble and restart the printer.

If that doesn’t help, reconnect the sensor’s ribbon cable on the print head board. Only if the error persists after that is the sensor replaced.

Nozzle temperature error

Two parts are responsible for the hotend temperature: the ceramic heater and the thermistor (NTC). On the X1 they come together with the hotend fan in the complete hotend assembly, so it’s often enough to replace that rather than the board.

1. Bring the nozzle temperature down to 50 °C or lower and turn the printer off.
2. Remove the head’s magnetic cover and check three plugs: the larger 2-pin one for the heater, the 4-pin one for the hotend fan and the very small 2-pin one for the thermistor.
3. A plug should sit straight and all the way in. A skewed or half-unplugged connector gives the same errors as a burnt-out thermistor.

If you have to remove the heater and thermistor and the thermal paste has hardened, don’t force them. Apply alcohol to the paste, wait about 5 minutes for it to soften, and only then carefully take the parts out.

The bed won’t heat up

What the screen shows matters here.

The bed temperature reads 0. The printer simply isn’t getting data from the bed sensor. Check the cable from the main board to the bed and the bed thermistor’s 2-pin connector. These connectors are secured with white silicone — if there’s no visible tilt or pulled-out pin, just press them firmly back in.

The temperature isn’t 0, but the bed won’t heat. Then the problem is the heater’s power supply: the bed power cable or the AC power board. If you have a multimeter, measure the resistance across the bed heater’s two pins with the printer unplugged — it’s normally about 50–60 ohms. No reading means a broken cable or a burnt-out heater.

Checking the voltage on the power board means working with mains voltage. If you don’t have electrical training, skip this step and contact a service centre.

The head cable and the cable chain

The toolhead cable runs from the main board to the extruder board in the head, and it flexes thousands of times in the cable chain as the head moves. Signs it’s damaged: errors appear at a certain head position, the printer restarts while moving, and sensors drop out and come back.

• Inspect the cable where it bends and near the connectors for fraying, kinks or torn insulation.
• The cable chain is replaced if it keeps coming apart or has broken links.
• The connector between the main board and the head board is keyed. Plugged in the wrong way round, it shorts the power — the printer will show an HMS error or won’t turn on at all.

After any work on the head electronics, run a printer calibration: if it passes, everything is connected correctly.

When it really is the board

If the connectors are checked, the cables are intact and the sensors are clean but the error keeps coming back, then it’s the board’s turn. Write down the HMS error code from the screen: it shows which assembly the printer considers faulty, so you can get the right board instead of replacing everything.

Need a part? Write to us with your printer model and the HMS error code — we’ll tell you exactly what to order. For quick diagnostics, use the printer diagram.