I dont see anything that relates

Double check that bobbin thread is correctly threaded through its tensioning path.
If it sews fine when sewing a straight line or zig-zag stitch you might have to loosen off the top thread tension a bit, or tighten the bobbin tension.
There is usually a small screw that controls the bobbin tensioner that can be tightened slightly to adjust bobbin thread tension. Do this little bit at a time and test after each adjustment.
Be careful when adjusting, take clear photos before touching anything so that you can put them back where they were if need be. Good luck.

Sounds like something you should have a technician look at.

if the bobbin winding has been switched back to normal sewing then there could be something wrong with the computer

Define "prematurely". Bobbins shouldn't fill to the edge of the bobbin. Are they wound evenly? Uneven winding can cause the winder to stop early.

does it sew ok straight stitch but not zigzag?

No, sewing machines that use bobbins don't have an adapter like that. It would be difficult to get the bottom tension right working off the spool. The best solution is to fill several bobbins in your thread color before starting to sew. Then when you run out, swap in a new bobbin.

Some advanced machines will warn you when the bobbin runs low. (I've seen the feature on the machines with touch-screens.)

I wish that I had better news for you. A serger might be a an option to consider. They don't use a bobbin and can be used for some sewing projects. You can still run out of thread on one cone before the others run out. (Those machines use 3-4 threads at a time for the basic stitches. The knife can be lowered if you don't want to trim your fabric while stitching.)
Cindy Wells
(I've got a Singer Touch and Sew and usually don't run out of bobbin during a seam. I will swap bobbins when they are still 1/4 full at times if I get concerned about the bobbin running out.)

Hi! Sounds like you're doing everything right to me, so let's see.

By not getting a straight stitch on the bottom, do you mean that the bobbin thread is loopy? If so, then most likely you have to reset the tension. Get a scrap of jeans material and practice on that....it would be great if you could use different color threads on top and in the bobbin, but that might not be practical if you don't have the jeans thread in different colors already.

You'll be adjusting the top tension, because even tho the top stitch looks perfect, it may not be tight enough to pull the bobbin thread up into the fabric where it belongs.

Sew a couple of inches on your scrap, then stop and check the bobbin thread. If it's loopy, you can also see the top thread on the underside. (Which is why using two colors is helpful.) With the pressure foot down, tightened the top tension just a bit. Sew a few more inches and check again. Keep on sewing, checking, and adjusting until you can't see any (or almost any) top threads on the bottom or bobbin threads on top.

Here are a couple of other ideas to check:

1. Make sure your bobbin is inserted correctly. If I happen to put one in backwards by mistake, the bobbin will make a lot of clanking noises.

2. Using your flywheel, lower the needle all the way through the stitch-making process to see if it's hitting anything along the way.

3. Oil your machine.

4. Make sure all the screws etc on your throat plate (also called needle plate) are tight. (I've had mine get loose and that will definitely throw a knock into the works!)

Check out these ideas and let me know if anything works, or if the problem is still there, ok?

Happy Sewing!

Robbie

You need to adjust the tention on you thread bobbin and on the needle....also, check to see if the needle is touching the plate or the foot.

I have had this problems too. Most of the time it is just a simple adjustment and cleaning.

Good Luck

Perhaps the bobbin winding mechanism is stuck. Probably needs service.

Also, check the bobbin and bobbin case. Perhaps there is some thread stuck or it is not securely threaded through the tensioner.

The second microswitch that is located just to the right of the bobbin winder stop tells the machine that it is set to wind a bobbin.

If the machine does not indicate that the bobbin winder is engaged, the second microswitch is not the problem. The bobbin winder itself is what shifts the clutch. If it is pulled downward, the clutch is disengaged and the upper shaft does not turn. Place your thumb under the bobbin winder, push it upwards and the clutch automatically re-engages and the shaft will turn.

Be very careful with the touch screen cable with the front cover off. If it has the older style cable on it, they are very delicate when releasing and reconnecting. If you put the front cover back on and the touch screen does not work, this will be the most likely problem. You will need to have the touch screen replaced.

You need to get your bobbin winder turned off first, then worry about the stop contacting the thread. If the stop is not tripped, then it is in its normal position and everything should work fine.

When not filling a bobbin, simply raise the bobbin winder and you should be ready to sew. Look at the opening around the winder shaft in the front cover and you will need to have it up and to the right. Just push the shaft with your thumb.