Well my Brother PE 770 just went into retirement. I've had it for three years and it served me well, but after Hurricane Sandy I had it into the shop twice -- at $125 each time. Not sure if the banging around and dampness had anything to do with the problems.
Over the last couple of weeks it has been shredding thread and getting into a snarl in the bobbin case. I did everything including taking the casing off the top to check for wayward thread (helped by a Youtube video).
I decided that rather than pay another $125 or more at the repair shop that I was using, I'd call the shop where I purchased it online -- Mr Vac and Mrs Sew to see if they did trade in's. They didn't. Happily they are a short drive away. Surprise! I told them I was ready to buy a new one rather than keep paying for repairs. The last one was for a burr on the bobbin case and Mrs Sew told me that I could have just bought a new bobbin case for $25! She said it was ridiculous to buy a new machine. They told me to bring it in and they'd look it over for free!
Mr. Vac did everything I did and then some but it was still doing awful things. Sending it back to Brother was going to cost more than I wanted to spend at this point, so I told them I wanted to buy a new one. Mrs. Sew tossed in a huge case of thread, a case of pre-wound bobbins, a thumb drive and a tote! I am one happy camper!
And now I have the old one to play around with in my spare (haha) time! Actually, the guy who did the Youtube video is one of their customers so I'm going to contact him to see if he can work his magic on it.
Mr Vac and Mrs Sew did give me some excellent tips - put your bobbin in counter clockwise. It makes a difference!
Mr. Vac told me never to use titanium needles. He said if there was something that caused the needle to break you wanted it to break rather than damaging something in the machine.
A long time ago I was having another issue and called them up. He told me not to use the spool cap. I stopped and haven't had an issue since.
Happily stitching with their thread -- which is wonderful!