On multi-needle commercial machines, there is a sensor that tells the machine which needle is currently selected. This sensor also keeps the drive mechanism from trying to sew between needles or other such potentially destructive things.
On my machine, the Butterfly 1501 B/T, the sensor is a 10 turn 1kohm
potentiometer that is held inside the needle changer cam drive with a set screw.
Well, it broke. The potentiometer would
not turn, which I verified by taking out the set screw and trying to turn the potentiometer
in both directions.
The company I bought it from was unresponsive, so I found the part number
and ordered a replacement. The part
number in the manual is not the actual part number though. The true part number is 7276R1KL.25
manufactured by BI Technologies. Be
careful and check your machine as there are 3 parts that are almost identical.
The 7276R1KL.25, 7276R10KL.25 and 7276R5KL.25 all look exactly the same; the
difference is how many ohms they are (1k, 5k, or 10k). According to the part number, my machine used
the 1kohm version; 7276R1KL.25
The potentiometer is soldered directly to the wire harness, so first it has to be removed. Notate which color wire goes where so you remember for the replacement.
Once all wires are cut, you can either solder on the replacement, or do what I did; build a connector. I used the header from a 60mm computer fan and the socket connector for the same. First, I soldered on the 3 pin connector to the replacement potentiometer and used shrink insulator around the terminals. Grid is 1" squares by the way.
Then, I soldered on the 3 pin header to the existing wires on the machine; again covering with shrink insulator.
Once the replacement is connected, you have to manually turn the potentiometer before tightening the set screw so that the machine is set to the correct needle. Meaning if the machine is on needle 6, turn the potentiometer until the display on the machine says needle 6, and tighten the set screw that holds the shaft of the potentiometer into the needle change motor shaft.
Test it by moving it by hand from needle 1 to needle 15; making sure the machine is displaying the correct needle number at each needle. If the machine doesn't, readjust the potentiometer until it does. Once completed, have the machine change needles a few times to make sure it can automatically understand the needle setting.