I’ve been giving my sewing machine the evil eye from a distance, it sits on my dining table & its been playing up from the day I got it 
(its less than 6mths old).
You see, the tension has never quite been right no matter what I did to it, so I played with the tension – no luck.
Put it back on the table for another week & deconstructed it & managed to fix the needle position which was also never correct (roll eyes), it was constantly hitting the foot & it wasn’t bent needles… the I played with the tension & whoopee! it worked just for all of an evening!
Last deconstruction – so I try to put the little lever behind the tension dial in a different position - when I pulled it apart slowly the first time I saw how it came out & put it back the same way – but I put it back together & set all the tension back to normal & we have perfection!
The darn stupid people who put it together put the tension arm in incorrectly at the factory – what happened to QC??!! 
I really hadn’t wanted to have it sent away because a) I figured they’d find a reason to charge me for a service or b) it would be gone for some time & I needed to get things done.
Thankfully I used to watch my dad do allsorts when I was a kid, so have a little mechanical inclination 
