I Have FHSM-505. PURPLE ONE. I SEWED ONE time, stitches were perfect, second time bobbin thread is bunching up. Didn't make any adjustments. How do I fix
Probably your top tension is too low or completely off. If your tension dial is at zero then change it. Your tension can be too low too because the machine is not threaded properly and so the thread is not in between the tension discs correctly. Your thread is bunching up underneath your fabric because the top tension isn't tight enough to pull the bobbin thread up into the centre of your fabric. I hope this makes sense to you.
Answers & Comments
Probably your top tension is too low or completely off. If your tension dial is at zero then change it. Your tension can be too low too because the machine is not threaded properly and so the thread is not in between the tension discs correctly. Your thread is bunching up underneath your fabric because the top tension isn't tight enough to pull the bobbin thread up into the centre of your fabric. I hope this makes sense to you.