Years ago my hubby bought me a Brother electronic machine (I still have it) and the tension kept going out of whack. I took it in 3 times over a couple years and each time I would ask the repair guy what he did to fix it. He'd give me all kinds of vague double talk. I knew it was a tension issue so after the 3rd time I finally figured out on my own it was my bobbin tension and I just needed to readjust it. Oddly enough, I only had to adjust it once and it's been working perfectly (around 25 years worth) ever since!! Kinda makes you wonder. And yes, I found a new service man.