Dead Sewing Machine or Dremel Tool Motor Answered
A woman asked me to look at her sewing machine. The motor was dead. A new foot control did nothing. A dealer seemed disinterested in looking at it for repairs, but wanted to sell her a new machine for $700+.
Attached is a photo of the commutator from her machine's motor after I cleaned it up enough to run again. After 15 years of use there was so much oxidation and contamination from brushes arcing that an Ohmmeter showed infinite resistance (open circuit) across the commutator, unless readings were taken on the brighter copper colored portions of the commutator. (The brushes are still good.) Then I got reasonable readings, indicating there was actually an unbroken circuit across the armature coils. Removing shrouds and getting to the motor was the most difficult part. Then I turned the motor by hand while I held 500 grit sandpaper on the commutator until it was clean and bright. The motor runs like new again. The owner is very happy. (I made this fix as a favor, not to gain income.)
I had expected something like I found in a Dremel tool that quit working. With an Ohmmeter I found a break in the circuit between the field coil and a terminal pin. (I was able to bridge the broken connection and the Dremel workes again.) Another sewing machine did not run, and the problem was found to be a bad electronic circuit board no longer available. That machine had to be replaced.
But, sometimes somethng so simple as a very dirty commutator is the only problem and is easily cleaned so the machine works perfectly again.