My brother pe770 jamming up and i get this error msg that says check and rethread upper thread

SOURCE: I have a Brother SE-270D

its the problem of the timing belt in your machine its extra loosen or extra tightned or is slightly came out of its position or finally broken.
as the machine is proper just missing the proper speed as it should be .
it is running continuosly as you stated.
check the timing belt and make it proper if its worn out and needs replacement this is how its done

There is an adjusting screw on the right side of the machine head. Follow the motor bracket to the machine head and loosen that big old screw or bolt which will raise or lower the motor giving you slack to remove or replace the belt.

feel free for further queries
thanks

SOURCE: My brother PE-400 sewing quit sewing

The "race" on your machine needs adjusting. Remove the bobbin cover, bobbin, & case. What you have left is the race, it moves when you turn the large wheel on the top right of machine. The needle also moves up and down. There is a hook on the race that catches the needle thread. Try moving the race to the line up with the needle. It may take a couple of trys but it should do the trick. Also clean any threads that may be caught on or arround the race. Hope this helps!

SOURCE: not sewing - jamming

Could it be that the feed dogs are down? I also have the 15358 and when I opened the bobbin area to clean it, I had this problem. Apparently, when you open the clips around the outside of the casing, it pushes the lever that adjusts the feed dogs to the right (lowering them). I didn't even realize it at first. Check your manual for adjusting this lever to raise the feed dogs. That might solve your problem.

SOURCE: won't catch bobbin thread

In order to see whether or not my euro-pro 9110 had a timing issue, the service rep had me change out the needle (making sure I was using anything but a Singer brand needle--they do not work in these machines). I re-threaded the needle, took out the bobbin casing and the plastic ring encasing the bobbin, then lowered the needle to see if the hook on the metal ring holding the bobbin actually catches the thread on its own. If it doesn't catch, it's a timing issue and needs repair. They can walk you through this process of troubleshooting and set up repair if need. Call Eruo-Pro's customer service center for sewing machine service and repair at 800-798-7395

SOURCE: Brother pe770 bobbin thread is showing on top of fabric.

First check threading. If it is done properly, then it's probably because it is dirty between the lower tension blade and the bobbin case body. Remove this blade, clean, reassemble and it shoud work.