There could be several reasons why the upper thread keeps breaking.

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1. The upper thread could be installed incorrectly. Rethread the machine according to the instructions in the manual. 
2. The upper thread tension could be set too tight. Set the tension to the best thread tension setting or less.
3. Make sure the spool of thread is installed correctly using the correct size spool cap for the size of spool.
4. Make sure the needle is correctly inserted with the flat side facing the back and pushed up into the machine as far as possible.
5. The needle could have been damaged or bent. If so replace with a new one.
6. The lower thread tension is incorrect, the thread does not roll out of the bobbin case smoothly. Adjust the lower thread tension.
7. The bobbin thread is not wound correctly, check that the bobbin is wound so that it is about 80% full and check the thread is evenly wound.  If the bobbin is not correctly wound, rewind the bobbin.
8. The thread density of the embroidery data is too fine, three or more overlapping stitches are being sewn. Using a data design system, correct the thread density and overstitching settings in the embroidery data.
9. The embroidery data contains stitches with a pitch of zero. Delete all stitches with a zero pitch.
10. The embroidery data contains many stitches with an extremely small pitch. Delete all stitches with a small pitch.
11.  The fabric is not taut. Firmly set the fabric in the embroidery frame so that it is taut.
12. The thread is loose in the hook area or the hook does not rotate smoothly. Remove the loose thread.
13.  The thread quality is poor. The thread quality is too weak due to the age of the thread. Replace the thread.
14. There are knots or tangles in the thread. Remove any knots or tangles.
15. A bobbin designed specifically for this machine is not used. Be sure to use the correct bobbin
16. Needle and thread are incorrect. Be sure to use the correct thread and embroidery needle.
17. In the cases shown below, consult nearest authorized Dealer or Service Center.

• The area around the hole in the needle plate is damaged.
• The needle hits/touches the needle plate.
• The presser foot is set too high and not correctly positioned. The needle hits/touches the presser foot.
• The area around the embroidery foot hole is damaged.
• Sliding surface on hook race is not smooth.  There are scratches or burrs on it.
• The play between the hook and the race is too much.
• The space between the hook stopper and the hook cannot be adjusted.
• The automatic needle-threading mechanism is broken.