Before I start on what fault might cause what problem, I need to talk about the theory of LOGICAL TROUBLESHOOTING. I have taught a university level course on LOGICAL ELECTRICAL TROUBLESHOOTING to expert (?) Government maintenance techs for a few years now, and have found that most people (even the experts) approach fixing problems with a random hap-hazard approach that has little chance of repairing anything and a great chance of making things much worse. 

Be patient and think before you act; just as with a lot of other things it is the APPROACH that counts. Proper Troubleshooting of a sewing machine or serger (or any appliance) is nothing more than what you view on the television when you watch CSI or NCIS or Monk or Sherlock Holmes or Criminal Minds. You're probably wondering what do the shows have to do with troubleshooting of your sewing machine?  They are all detective shows... where they are detecting or finding the cause by observing the clues or symptoms.  I do the same with sewing machines, automobiles, computers, refrigerators, etc.... it doesn't matter what it is. The logical approach works on both murders and machines. Confused?

Let's take a common two cell flashlight that won't light up as an example. Why doesn't it light? You would probably simply guess that  it is the batteries or the bulb, and you may be right. You may also be wrong as their are at least 30 other possibilities that can keep that bulb from shining. Yes, you hit the most probable......  but in the big picture of all the flashlights in the world, your problem is just as likely to be one of the other 30 as it is the battery or the bulb. So how do we do use this logical approach?

What you need to do is always use the Scientific Method and look for "cause and effect". Still or more confused? If you really want to learn more about the approach of LOGICAL TROUBLESHOOTING, consider buying and reading my course book titled "LOGICAL ELECTRICAL TROUBLESHOOTING."  You can preview the book thru the website link.

Before we actually start troubleshooting, we need to make sure that the simple things that we often ignore are addressed:

A. Always make sure the machine is properly oiled (not too much and not too little), that it is properly threaded (refer to the instruction book), and that the lower bobbin and bobbin case are lint-free before sewing. They also need to be clean because old oil, dust, and fabric lint will combine to gum up everything, and drag down the motor. Speaking of oil... only use the correct sewing machine oil, and not 5 weight auto oil. Even the right oil gets old breaks down in time because of heat and dirt..... and eventually the lighter petroleum distillates evaporate away leaving a brown varnish on your machine shafts and bushings. This varnish needs to be removed regularly by you or your sewing machine technician before re-oiling. If not, it will just build-up over time and some day stop your machine.

B. Use a needle size that is right for the fabric and thread weight. Be sure the needle is the correct one for the sewing machine, straight and sharp. Change needles frequently when sewing synthetic fabrics.

C. Use the same thread in the bobbin as on the spool unless for special effect. This lessens the chance of having tension problems.

D. Pull the bobbin thread through the needle hole in the needle plate before starting to stitch.  Some newer models do not require this step.

E. As you start to stitch, place the threads under the presser foot and hold them to the back of the machine. Some newer models do not require this step.

F. Turn the hand wheel toward you to start the stitching. Some newer models do not require this step.

G. Start and stop the machine with the needle and thread take-up lever in their highest position. Some newer models do not require this step.

H.  Once the tension on the upper thread and bobbin thread are balanced, change only the upper thread tension for any slight change in tension.

I.  To turn a corner, stop the machine while the needle is still in the fabric. Raise the pressure foot and turn the fabric, using the needle as a pivot point. Lower the pressure foot and resume sewing.

J. Protect your sewing machine from dust and grime between sewing projects by covering it or putting it inside the sewing cabinet or machine case.

Common Sewing Machine Problems (from my experience).

1. THREAD or THREADING PROBLEMS caused by cheap, or old or deteriorated thread along with incorrect threading. (25%)

2. CLEANING PROBLEMS caused by lint, dirt, and tangled thread packed into the machines moving parts. (22%)

3. LUBRICATION PROBLEMS caused by too much, too little, or wrong type. (15%)

4. NEEDLE PROBLEMS caused by bent, dull, incorrect type, or needles inserted incorrectly. (13%)

5. MINOR ADJUSTMENT PROBLEMS such as Tensions, etc. (10%)

6. MINOR PARTS PROBLEMS such as Bobbin case, hook, needle plate, etc. (7.5%)

7. MAJOR REPAIR PROBLEMS such as complex parts or adjustments needed. (5%)

8. ELECTRICAL PROBLEMS such as foot control, motor, or power cord. (2.5%)

If the Thread breaks:

Incorrect tension:

Skipping stitches:

Fabric won't feed:

Needle breaks:

Machine locks up:

Machine runs slow: