there really are no tiny parts in the tension assembly, they are pretty simple.... a couple disks and a spring.... just pinches the thread. I think people are unreasonably scared of them, ( but then again I have messed up a lot of stuff in my life assuming I knew more than I did ) As far as your stitches... it looks as though the upper thread is no looping.
at the risk of sounding like captain obvious... are you SURE you are threading it correctly? other than that I believe you can wind the take up spring up ( or down) I am wondering if there is an extra turn of tension on you spring ? also the "split" stud that your tension assembles around is movable ( removable ) and it is possible it was removed and put back in wrong ? these are thing I need someone with actual 15 experience to chime in on.