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If you look at the inside of a sewing machine, you will find a series of belts, wheels, levers and shafts. Some of these look fairly fragile and easy to break. But in reality, most sewing machine problems are most often due to operator error or poor maintenance, not mechanical failure. To prevent failure, the manufacturer's guidelines should be closely followed. Couple that with regular maintenance and the machine will perform reliably for years. Major repairs, particularly on computerized models, are best left to a specialist. But there are some things you can do.

Needle and stitch formation problems
The workings of the needle, feed dogs and shuttle hook are quite precise. Small variances can cause large problems.
? If the thread keeps breaking, it could be due to a bent, dull or burred needle. Always check the needle first.
? If the material feeds unevenly, the fault might be the feed dogs. Check for lint build up between them, then check their alignment by placing a needle, flat side down, next to them. Turn the hand wheel until the feed dogs rise. If their teeth are higher than the needle, have the machine professionally serviced.

Thread tension adjustments
If thread loops appear on the fabric's back side, the tension is too loose. If the fabric puckers on the front side, the tension is too tight. First adjust the needle thread tension:
* make sure machine is threaded and presser foot is down
* turn thread tension dial as needed; high numbers for more tension, low ones for less.

Cleaning the thread tension assembly might also help. Problems can also occur if the bobbin thread tension is improperly set. To test bobbin:

* Wind the bobbin and suspend it with its case from the thread
* The case should drop two to four inches.
* If it drops farther, the thread is too loose; if less, it's too tight.

To adjust the bobbin:
* Turn the screw on the bobbin case
* Only tiny adjustments are needed.
* Turn screw clockwise for more tension, opposite for less.

Mechanical parts
Frequent thread jams or breakage not caused by improper threading may be a problem in the needle or bobbin thread assemblies. Keep these parts free of lint and dust.
* Clean thread tension assembly by sliding paper or a toothpick between discs to remove tangles of thread.
* Clean bobbin thread tension assembly by sanding off burrs or rust with a very fine emery cloth. Keep sanding dust out of assembly. Brush out lint.
* Replace worn or damaged parts as needed.

If the fabric moves unevenly, the feed dog teeth may be dull.
* Raise the presser foot.
* Remove needle and needle plate.
* Remove screws holding feed dogs in place and lift them out
* Clear out lint and debris with tweezers
* If too dull, replace

Also, the presser foot might be out of alignment.
* Open face cover.
* Turn the presser bar screw until foot is straight.
* If this alters pressure exerted on fabric, have the machine serviced.
* Replace a scratched or damaged foot.

Servicing motor and electrical system
This is fairly simple and mainly involves removing the cover and cleaning parts. Remove the parts you feel comfortable in removing, remembering what goes where to replace. Broken wires, loose connections, worn brushes and dirty, corroded contacts are the most common and are easy to repair. Remember to disconnect the machine from power before attempting this. If you are electrically inclined, you should have little trouble. If not, have the machine professionally serviced.

To service the foot pedal:
* Disconnect power cord
* Open the housing
* Brush or blow away accumulated lint and dirt, particularly around contact areas.
* Lubricate pivot with a dab of grease.

Servicing the drive belt
A drive belt connects the motor to the hand wheel, which in turn runs all of the other functions. A worn or stretched belt can cause faulty operation.
* Unplug machine
* Remove top cover
* Remove screws holding hand wheel.
* To remove belt, stretch over pulley, then lift off.
* Replace a worn or damaged belt.

For problems not mentioned here, consult your manual, service technician, dealer or the manufacturer.