Brother XL-5012 sewing machine

Sounds as though the top thread is not being captured by the rotary hook. Check for a bent needle and clean bobbin, hook, and feed dog area.

http://support.brother.com/g/b/manuallist.aspx?c=gb&lang=en&prod=hf_xl501250215032euk&flang=English&type3=348&type2=69


User Guide Manuals XL 5011 5012 5021 5031 5032 United Kingdom Brother

you may be able to enlarge the manual page:

Brother XL 3030 User Manual Page 60

The hook (half-moon piece) needs to go in first, but you may need to wiggle it to seat it and then hold it while you fasten the outer retaining ring (hook race). Flip the levers up to hold the ring in place. Then install the bobbin case.

How to Clean and Maintain your Sewing Machine at Home Front Loading Bobbin

FWIW, my machine oiling instructions say to apply a drop of good quality oil on the outer edge of the hook race lip where the hook rubs as it turns. But, your manual should explain where to oil.

...

Download manual

try adjusting the top tension and see if that help the bobbin stitches
to look normal
here is a 2 links for a free manual, check and see with is the right one
for the machine

http://www.brother-usa.com/ModelDocuments/Consumer/Users%20Manual/UM_XL_2600_2610_3500_3510_EN_206.PDF

http://www.brother-usa.com/ModelDocuments/Consumer/Users%20Manual/UM_XL_2600i_ENES_1478.PDF

call your local Brother dealer.

try this link for a free manual and see if it helps with bobbin tension

http://www.brother-usa.com/ModelDocuments/Consumer/Users%20Manual/UM_XL_3025_3027_3030_EN_447.PDF

Here is a direct link to the .pdf file:

http://www.brother-usa.com/ModelDocuments/Consumer/Users%20Manual/UM_XL_2600i_ENES_1478.PDF

Here is the webpage for the manual and accessory documents (underneath 'Your Results'):

http://www.brother-usa.com/manuals/default.aspx?PGID=3&R3ModelID=XL2600i

http://www.brother-usa.com/ModelDocuments/Consumer/Users%20Manual/UM_XL_5130_5232_5340_EN_208.PDF

You can download the manual from the link below: http://welcome.solutions.brother.com/BSC/public/files/dlf/doch000062/xl513052325340ug01enesfr.pdf It has diagrams of how to thread the machine. There is also a FAQ section: http://welcome.solutions.brother.com/BSC/public/us/us/en/model_top/HomeSewingMachine/hf_xl5130eus.html?reg=us&c=us&lang=en&prod=hf_xl5130eus Please update the question & let us know if the information given was useful to you - Good Luck!