Fracktal 3d Printers come with 3 Limit switches.

X axis

Y axis

Z axis

Whenever these switches fail, the printer faces certain issues, like not being able to move in a certain direction or going and crashing at the edges.

Below, we have listed the indicators of limit switch failure and how to fix them.

1. Checking Limit Switches.

1. Access the printer via OctoPrint.

2. Bring the carriage and Bed to the center. If you can’t control them using the onscreen buttons, turn off the machine and manually push them.

3. Give M119 command in the terminal.

4. You should get this output

> M119

Reporting endstop status
x_min: open
y_min: open
z_min: open

Here, the open status indicates that the limit switches are not triggered. Since the carriage and bed are at the center, the limit switches are not pressed. So they are showing open. In case a limit switch is faulty, it will show triggered even without being pressed.

5. If all limit switches are showing correct output, do the next step. In case they are showing wrong values, note the limit switch, and later in this article, you will be told how to fix it.

6. Home the XY carriage and Bed to Z home. With XY and Z at the home position, all limit switches should be triggered.

7. Give M119 command in the terminal.

8. You should get this output if all switches are correct.

> M119

Reporting endstop status
x_min: TRIGGERED
y_min: TRIGGERED
z_min: TRIGGERED

NOTE: Limit switches work on OPEN or CLOSE status. There are chances of the switch giving both False open and False close status. So you need to check the switch in both statuses.

Troubleshooting:

Note: The limit switches on Fracktal Printers are normally open types. There will be a small voltage flowing through the switch. Whenever the switch is pressed, the flow of current is stopped, and it shows the Status as TRIGGERED. In case there’s a loose contact or wiring issue, it will show as TRIGGERED because there is no current flow.

Once you identify the limit switch that is giving a faulty reading, there are 2 possibilities.

1. Faulty Limit switch.

2. Connectivity.

A limit switch can be tested by 2 methods.

1. Using a Multimeter.

To check the limit switch using a multimeter

set the multimeter in connectivity mode> connect to ends of the limit switch wire to the multimeter probes> and if the switch is fine, it should give a beep. If the switch is spoiled, it will not give a beep.

Check without pressing the button. You should get a beep if the switch is fine.

If you get the beep, press the limit switch, and the beep should stop. If the beep does not stop when you press the limit switch, it means the switch is damaged.

Check while pressing the button. If the limit switch is fine, you should not get a beep when the button is pressed

2. Trial and error (In case you do not have a multimeter)

If you do not have a multimeter, replace the faulty limit switch with another limit switch in your machine. If the X limit switch is damaged, remove the Y limit switch and plug it into the X limit switch port. And check Octoprint and m119. If the output is fine, then the limit switch is the issue. If the same issue repeats even after changing the limit switch, then wiring is the issue. You need to check the connectivity and decide which part is damaged.

If the limit switch is fine, still the OctoPrint is still showing wrong values, you need to check connectivity.

To check connectivity

How to Test for Continuity with a Digital Multimeter #

Basic idea of using an ammeter.

Turn the dial to Continuity Test mode. It will likely share a spot on the dial with one or more functions, usually resistance (Ω). With the test probes separated, the multimeter’s display may show OL and Ω.
If required, press the continuity button.

First insert the black test lead into the COM jack.
Then insert the red lead into the VΩ jack. When finished, remove the leads in reverse order: red first, then black.
With the circuit de-energized, connect the test leads across the component being tested. The position of the test leads is arbitrary. Note that the component may need to be isolated from other components in the circuit.
The digital multimeter (DMM) beeps if a complete path (continuity) is detected. If the circuit is open (the switch is in the OFF position), the DMM will not beep.
When finished, turn the multimeter OFF to preserve battery life.

Continuity testing overview #

Continuity is the presence of a complete path for current flow. A circuit is complete when its switch is closed.
A digital multimeter’s Continuity Test mode can be used to test switches, fuses, electrical connections, conductors, and other components. A good fuse, for example, should have continuity.
A DMM emits an audible response (a beep) when it detects a complete path.
The beep, an audible indicator, permits technicians to focus on testing procedures without looking at the multimeter display.

Fracktal printers have custom-made PCBs and use FFC instead of normal wires to reduce the mess by having too many wires. To check connectivity issues, you need to use a multimeter.

Note: Certain components follow a closed-loop circuit. Closed-loop systems will show connectivity even though there is a break in the circuit. So if you are testing for continuity of the closed loop circuit, make sure you remove the end component and make it an open loop (Ex, remove the Limit switch, hot end, thermistor, etc, in case you need their connectivity )

To check the continuity of the circuit, there are test points on the PCBs.

Step1.

Check the component whose continuity you have to check. (Ex – Limit switch)

Step2.

Find the test point for the component in the first board, considering the Carriage board. (ex, X-axis Limit switch has test point X-LIM)

Step 3.

Find the test point on the other board. Consider Chassys board. Keeping the two multimeter probes on the required test point should give you a beeping sound if there is no problem with the continuity of the circuit. If there is a breakage/Issue with the circuit, the probe will not beep.

Ex: When you keep probing the X limit test point of the carriage board and on X limit test point of the chassis board, it should beep if the connections are fine. If the connection has an issue, the multimeter will not beep.

4. Once an issue is found with the connectivity, you need to check the FFC for breakage or damage.

5. If you are checking connectivity between 2 boards where there is a PCB in between, you need to check connectivity between the individual boards to determine where the connection is faulty.

Ex: If you check connectivity between a point in the carriage board and between the MKS daughter board and find the connectivity to be faulty, you need to check connectivity between the Carriage PCB and Chassis PCB. And then between Chassys PCB and the Daughter board of MKS.

Note: If the connectivity is fine, but still there is no power output at the connecting pi, then there is are chance that the board is damaged. To confirm if the board is damaged, you need to check connectivity between the test point and the output pin, like the JST pin or the FFC connector.