Many sewing machine technicians resist servicing sergers because they look strange.
While "regular" sewing machines form lock stitches using a thread from above and threads from a bobbin beneath, overlock machines or sergers use multiple threads (three, four, five,...eight) and use strange looking loopers to form both a lock stitch and an over casting edge wrapping stitch. The overlock seams, overcasts the fabric edge, and trims the fabric all in a single pass at twice the speed of the common home machine.
The most common problems include threading difficulties, irregular tensions, and unreliable timing.
Threading is a challenge and must be performed in correct order (Upper Looper, Lower Looper, Needles). Use of a pair of tweezers and a manual needle threader greatly reduce threading problems.
The tension assemblies are essentially the same as those on regular machines, but the number of thread requiring tension can make it difficult to properly adjust. Tracing threads from the needle threaders that form the lock stitch seams and the loopers that form loops around the edge of the fabric help the technician to identify the problem tension adjuster.
Adjusting timings is usually easy and can be done without disassembling the machine. Applying the timing principles from oscillating hooks to the loopers quickly guide the adjustments.
Removing the bottom cover in many cases gives the technician sufficient access for easy servicing. This result makes servicing sergers faster and easier that most sewing machines.