I found a similar definition diagram, I don't know if it is this definition.
I believe it is, and that you labeled it exactly correctly.
I am a beginner in stepper motors and this is my first time disassembling a stepper motor.
I have maybe a dozen different types, but I am a hobbyist only. My background is in physics, and I do have some formal education in electronics, but mostly, I just read datasheets.
I don't know if I can repair this stepper motor at the moment. It looks like its circuit is very complicated and I have no idea where to start.
Did you already check the board with a multimeter, to verify the traces on the PCB are not shorted?
If the traces (4/B to 5/M or 2/O) on the PCB are not shorted, then it is likely one of the 4/B coils overheated, causing the wire lacquer to flow, and thus the short.
I disassembled the PCB above, see the picture, I don't know how to repair it next
Did you check the PCB yet for shorts?
If the short is in a coil, repair would mean re-winding that coil. I wouldn't even want to try to do that. Hopefully, the short was on the board only, and now gone?
Can you now measure the wire-to-wire resistances (DC)? That alone will tell if there is a short. If there is no short anymore, then measuring the inductances, just to be sure, would help.
If there is no short anymore, then soldering the wires back to the cleaned PCB would bring the motor back to working order.
Fortunately, there are several replacements available that should work for you in this case. The hardest part to obtain is the exact gear, so I would definitely try to extract and reuse that with a new motor. Moons Industries MS16HS4P6085 (see page 30 in the Catalog under Hybrid Stepper Motors at
Moons' Product Center) is the closest match I found online; I bet you can find an even better match by looking for a "NEMA 16 unipolar 6-wire stepper motor (39mm×39mm×36mm) with 5.8Ω to 7.0Ω phase resistance and 4.8mH to 5.8mH phase inductance", if you can visit Huaqiangbei Market in Shenzhen. Try to match the resistance on the upper end, so that your new stepper is less likely to burn out. (Higher DC resistance, lower DC current.)
Unipolar steppers can be simpler to drive than bipolar, since only one of the A1/B1/A2/B2 pins is energized at the same time, and only one polarity is needed. This is why Darlington drivers like ULN2003A are so popular with these: you just use a voltage that does not cause too high currents (that would heat up the stepper). ULN2003A itself drops about a volt, so when run from 5V, the stepper coil voltage is about 4V, and the current about 600mA. (Compare to bipolar steppers, which need either a full H-bridge, or a dedicated stepper driver IC.) Personally, I do prefer the bipolar ones, since DIP-footprint drivers like TMC2100 are easy to interface to and produce superior results (torque, sound) given the same size.