Objective: Identify and correct the most common sewing faults on the Janome MC6650 so your seams come out clean enough to sell.
Most 'broken machine' panics are actually simple threading or tension issues. Learn to read the fabric: the side showing the problem usually points to the opposite thread. Loose loops on the BOTTOM of your fabric mean the TOP thread is at fault — almost always because the presser foot was up when you threaded, so the thread never seated in the tension discs. Fix: raise the presser foot, rethread the top from scratch, pull thread through the discs, and lower the foot. Loose loops on the TOP of your fabric point to the BOBBIN: it may be inserted backward or seated wrong, so reinsert it so the thread unwinds in the direction shown on the bobbin case diagram. Skipped stitches usually mean a dull, bent, or wrong-size needle, or a needle inserted not fully up with the flat side facing the wrong way — replace it (flat side to the back, push all the way up). A 'bird's nest' jam of thread under the fabric means you started sewing without holding the thread tails or with the top unthreaded: stop, raise the needle and foot, gently pull the fabric free, snip the tangle, remove and clean the bobbin area, then rethread both threads. To undo bad stitches, slide a seam ripper under every third stitch on one side, cut, then pull the opposite thread — it lifts away in one pass. Always test on a fabric scrap after any fix before returning to your real project.
Example: You sew a seam on cotton and see a messy row of loose loops on the underside. Reading the clue: loops on the bottom = top-thread problem. You check and the presser foot was down the whole time but the spool ran into a tangle, so the thread slipped out of the tension discs. You raise the presser foot, re-thread the top thread completely, confirm it clicks into the take-up lever, lower the foot, and sew a test line on a scrap. The loops are gone and the stitch looks balanced on both sides — problem solved.
Try it: Deliberately create a fault: thread the top of your MC6650 with the presser foot DOWN, then sew a 10 cm line on a cotton scrap. Observe the loose loops underneath. Now fix it by raising the foot, rethreading correctly, and sewing a second test line. Finally, take the faulty first line and remove it with a seam ripper using the cut-every-third-stitch method. Keep both scraps to compare the bad and good seams.