Thread Sensor Replacement

If you need to replace the Thread Sensor follow the steps below, or see our video on Replacing the Thread Sensor (Acti-Feed Sensor). This installation is best performed by two people.


Previously, there were two models of Thread Sensors, the only difference is the color of the plastic side brackets/mounts for the sensor.  Functionality of the sensors with Black mounts and Red mounts is the same, and they are both compatible with all current machine models:  Thread Sensor PN: 34617. 


CAUTION!!  Handle the Thread Sensor Assembly carefully. DO NOT allow the PCB or bracket to hang by the wires, the wiring is extremely fragile. Although this assembly is resistant to electrical static discharge (ESD) damage, use normal precautions when handling electrical components. Parts that are damaged due to mishandling are not covered under the machine warranty.

1.  Turn the machine off.

2.  Trim all 16 threads by the pinch rollers.


3.  Remove the Front Magnetic Access Cover.


4.  Remove the Needle Case Cover by taking out the two screws holding it in place.


5.  Remove the Harness for the Thread Sensor PCB.

6.  Remove the Lock Nuts for the Thread Sensor PCB. Do NOT let the PCB board hang by its wires.


7.  Loosen but don’t remove the Allen Screw for the Thread Sensor. Be careful to not put any dents or scratches into the sensor’s tube with the Allen Wrench.

8.  Remove the small wires for the Thread Sensor from their clips.

9.  Apply finger pressure to both plastic end caps on the sensor bar. Apply this finger pressure until lock nuts secure the end clips. Once the Allen Screws are removed these end caps have the potential to separate. There are small components within the sensor bar that can fall out if the end caps do not hold them in. If these parts come out of the bar, it is unlikely they can be put back in the correct configuration. If they did fall out you will need additional technical assistance. Here are the available Melco Technical Support options. It can be helpful for one person to handle the screws, while a second person holds the end caps together.

10.  Remove the Allen Screws.

11.  Remove the Sensor Bar.

12.  Install Lock Nuts to secure the end caps.

13.  Apply finger pressure to the new Thread Sensor in the same manner as the previous step.

14.  Remove the Lock Nuts from the new Sensor.

15.  Install the new Sensor onto the machine with the two Allen Screws.

16.  Install the Lock Nuts for the Thread Sensor PCB.

17.  Make sure the small wires for the Thread Sensor are not hanging off or they will be pinched when reinstalling the Needle Case Cover.

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18.  Adjust the Static Clip.  The clip should make slight contact with the sensor.


19.  Reinstall the Needle Case Cover and both screws holding it in place, but leave them loose.


20.  Make sure there are no threads caught behind the Needle Case Cover.


21.  Make sure the top of the Needle Case Cover is seated in the top of the Needle Case.  You might have to carefully lift the cover up until it snaps into place.


22.  Tighten the screws for the Needle Case Cover.


23.  Reinstall the Front Magnetic Access Cover.


24.  Run a Thread Break Sensor Test on needles 1, 9 and 16.

25.  Replacing the Thread Sensor is complete.

26.  If the situation remains unresolved, you will need additional technical assistance and should contact Melco Technical Support.

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