I'm using Brother Poly thread on my Brother PE-770. Everything was fine until I changed needles. I followed the directions exactly. But now, when I embroider, my thread keeps unraveling and the needle unthreaded itself. I've went back to the old needle and tried different threads. Also when the needle does stay threaded for about 30 seconds, the stitches won't catch on the fabric. Please help

Usually misthreading, however, it could also be something else, ie needle, old or bargain bin thread, tension, burr or snag.

Why is my thread breaking

check that the needle thread tension is adjusted properly as it indicates that it is too loose

try changing the needle again, sometimes even new needle can be damaged
also check for burrs around the needle plate

Always make sure the hand wheel is at the exact top. Have you replaced the need recently? If it's bent, then the threader will not work. If the needle is loose or not all the way to the top in the holder, it will also cause the threader to not work.

I had many problems with tension until I moved the thread spool to the back on an outside stand. Check the thread guide path for lint. If everything is good then read the manual about adjusting the tension.

Timing this machine is not so easy but if U want to try... Remove the left bottom panel (one central screw), and look under. U will see by the rear the vertical gear making the hook turn. At the bottom of this gear, U will see a small allen. Slack this allen screw, LEAVE A TENSION ON THE ALLEN SCREW: eitherway the hook will not follow the gear when U bring back the assembly to retight the allen screw.
U can now turn the hook on the gear, allowing to change the timming.

Send the needle completely down and when it come up, the point of the hook has to arrive at 2.5mm. on the top of the hole on the needle.

A TRICK : It might be easier to slighly change the position of the needle in the needle bar. Check the timing and try to correct it but lowering a little bit the needle before tightening the scew, or cut a little bit top part of the needle with a grinder.

Just use a regular printer type cable. On newer models, they use a regular USB connection so it's easier to use USB keys

Are you saying that you changed the needle? You cannot tell if your needle has a burr on it or not. Because if you did, you may have messed up your timing and need service because it will take special tools and know how to fix it. . Try another needle one more time (make sure that the flat side faces away from you) and different thread. Rethread with your presser foot up, then pull the top thread, it should move smoothly, now lower the presser foot and pull the thread, it should barely move. This should seat the thread in the tension discs. Also, check that you aren't using the wrong size needle for the task at hand.

You need to sew the first stitch slowly. Lower the needle by hand and take up carefully. Pull the needle thread up and the bobbin thread should be caught in the formed loop and come with it. Pull them both to the back of the machine and sew.

My pe-150 embrodery machine is not grabing the tread right since I changed the needle out it keeps promping me to check my threading