Notes on the Troubleshooting and Repair of Small Household Appliances and Power Tools


  12.11) Wiring fluorescent lamps to remote ballasts

For reasonable distances, this should work reliably and be safe provided that:

1. This is only attempted with iron ballasts.  The fire safety and reliability
   of electronic ballasts that are not in close proximity to the lamps is
   unknown.  The ballast may fail catastrophically either immediately or a
   short time later as the circuit may depend on a low impedance (physically
   short) path for stability.

   In addition, there will almost certainly be substantial Radio Frequency
   Interference (RFI) created by the high frequency currents in the long
   wires.  The FCC police (or your neighbors) will come and get you!  This
   may be a problem with iron ballasts as well - but probably of less

2. Wire of adequate rating is used.  The starting voltage may exceed 1 KV.
   Make sure the insulation is rated for at least twice this voltage.  Use
   18 AWG (or heavier) gauge wire.

3. There is no possibility of human contact either when operating or if any
   connectors should accidentally come loose - dangerous line voltage and high
   starting voltage will be present with tubes disconnected.

Note: one application that comes up for this type of remote setup is for
aquarium lighting.  My recommendation would be to think twice about any
homebrew wiring around water.  A GFCI may not help in terms of shock
hazard and/or may nuisance trip due to inductive nature of the ballast
(both depend at least in part on ballast design).

  12.12) Problems with fluorescent lamps and fixtures

In addition to the usual defective or damaged plugs, broken wires in the
cord, general bad connections, fluorescent lamps and fixtures have some
unique problems of their own.  The following assumes a lamp or fixture
with a conventional iron (non-electronic) ballast.  Always try a new set
of fluorescent tubes and starter (where used) before considering other
possible failures.

1. Bad fluorescent tubes.  Unlike incandescent lamps where a visual examination
   of the bulb itself will often identify a broken filament, there is usually
   no way of just looking at a fluorescent tube to determine if it is bad.
   It may look perfectly ok though burned out fluorescents will often have
   one or both ends blackened.  However, a blackened end is not in itself
   an indication of a bad tube.

   Failure of the electrodes/filaments at one or both ends of the the
   fluorescent tube will result in either a low intensity glow or flickering
   behavior.  A broken filament in a fluorescent tube used in a preheat
   type fixture (with a starter) will simply result in a totally dead
   lamp as there will be no power to the starter.  The best approach is
   to simply try replacing any suspect tubes - preferably both in a pair
   that are driven from a single ballast.

2. Bad starter (preheat fixtures only).  The little starter can may go bad
   or be damaged by faulty fluorescent tubes continuously trying to start
   unsuccessfully.  It is a good idea to replace the starter whenever tubes
   are replaced in these types of fixtures.

3. Defective iron ballast.  The ballast may be obviously burned and smelly,
   overheated, or have a loud hum or buzz.  Eventually, a thermal protector
   built into most ballasts will open due to the overheating (though this
   will probably reset when it cools down).  The fixture may appear to be
   dead.  A bad ballast could conceivably damage other parts as well and
   blow the fluorescent tubes.  Ballasts for fixtures less than 30 watts
   usually do not have thermal protection and in rare cases catch fire
   if they overheat.  Defective fixtures should not be left operating.
   If the high voltage windings of rapid start or trigger start ballasts
   are open or shorted, then the lamp will not start.

4. Bad sockets.  These can be damaged through forceful installation or
   removal of a fluorescent tube.  With some ballasts (instant start,
   for example), a switch contact in the socket prevents generation of the
   starting voltage if there is no tube in place.  This minimizes the
   possibility of shock while changing tubes but can also be an additional
   spot for a faulty connection.

5. Lack of ground.  For fluorescent fixtures using rapid start of instant
   start ballasts, it is often necessary for the metal reflector to be
   connected to the electrical system's safety ground.  If this is not
   done, starting may be erratic or may require you to run your hand over
   the tube to get it to light.  In addition, of course, it is an important
   safety requirement.

Warning: electronic ballasts are switching power supplies and need to be
serviced by someone qualified in their repair both for personal safety as
well as continued protection from electrical and fire hazards.

  12.13) Why do fluorescent lamps buzz and what to do about it?

The buzzing light is probably a mundane problem with a defective or cheap
ballast.  There's also the possibility of sloppy mechanical construction
which lets something vibrate from the magnetic field of the ballast until
thermal expansion eventually stops it.

First check for loose or vibrating sheetmetal parts - the ballast may
simply be vibrating these and itself not be defective.

Most newer fixtures are of the 'rapid start' or 'warm start' variety and
do not have starters.  The ballast has a high voltage winding which provides
the starting voltage.

There will always be a ballast - it is necessary to limit the current to the
tube(s) and for starting if there is no starter.  In older fixtures, these will
be big heavy magnetic choke/transformer devices - hard to miss if you
open the thing.  Cheap and/or defective ones tend to make noise.  They
are replaceable but you need to get one of the same type and ratings -
hopefully of higher quality.  A new fixture may be cheaper.

The starter if present is a small cylindrical aluminum can, approximately
3/4" x 1-1/2" in a socket, usually accessible without disassembly.  It
twists counterclockwise to remove.  They are inexpensive but probably not
your problem.  To verify, simply remove the starter after the lamp is on - it
is not needed then.

The newest fixtures may use totally electronic ballasts which are less
likely to buzz.  Warning: electronic ballasts are basically switching
power supplies and are may be hazardous to service (both in terms of
your safety and the risk of a fire hazard from improper repair) unless
you have the appropriate knowledge and experience.

  12.14) Fluorescent lamps cycling on and off

This usually means that the tubes associated with one ballast are cycling
with a period in the 5 to 30 minute range.

There is a thermal protector in the ballast which cuts power to the tubes
that it feeds above a certain temperature.  It is likely that this is causing
the cycling behavior.  The ballast overheats, shuts off, cools down, starts
up, etc.  One or more of the following causes are possible:

* Bad ballast - shorted turns or other fault is causing overheating.

* Bad tubes - replace them and see how it behaves.

* High temperature location - did anything change?  Is it 110 degrees F
  in the shade (or in the room)?

* High line voltage - test with a multimeter.

* Bad starter (preheat fixtures only) - remove the starter with the lights
  on.  If the problem goes away, the starter is probably defective.

* The fixtures are being controlled by a photocell and light from the fixture
  is hitting the sensors and turning them off.

  12.15) Replacing fluorescent lamp or fixture components

Most of these parts are easily replaced and readily available.  However,
it is usually necessary to match the original and replacement fairly
closely.  Ballasts in particular are designed for a particular wattage,
type and size, and tube configuration.  Take the old ballast with you
when shopping for a replacement.  There may be different types of sockets
as well depending on the type of ballast you have.
It is also a possible fire hazard to replace fluorescent tubes with a
different wattage even if they fit physically.  A specific warning has been
issued about replacing 40 W tubes with 34 W energy saving tubes, for example.
The problem is that the ballast must also be correctly sized for the new
tubes and simply replacing the tubes results in excessive current flow and
overheating of the ballast(s).

  12.16) Why are those tiny tiny 4 watt fluorescent bulbs so expensive?

Can you say 'supply and demand' and 'economies of mass production'.  You
are comparing the price of the common F40CW-T12 lamp manufactured by the
zillions and sold in home centers for about $1 with specialty bulbs used
in a relatively few devices like battery powered fluorescent lanterns
and makeup mirrors.  These little bulbs may indeed cost up to ten times
as much as the much larger ones.

By any measure of materials and manufacturing cost, the 4 foot bulb is much
much more expensive to produce.  There is nothing special involved.

Chapter 13) Gas Discharge Lamps

Editor's note: This section is a condensed version of the document of the
same name available at: http://www.misty.com/~don/.  Special thanks to
Don Klipstein for help in editing of this material.

  13.1) Gas discharge lamp basics

Gas discharge lamps are used in virtually all areas of modern lighting
technology including common fluorescent lighting for home and office - and
LCD backlights for laptop computers, high intensity discharge lamps for
very efficient area lighting, neon and other miniature indicator lamps,
germicidal and tanning lamps, neon signs, photographic electronic flashes
and strobes, arc lamps for industry and A/V projectors, and many more.

Unlike incandescent lamps, gas discharge lamps have no filament and do not
produce light as a result of something getting hot (though heat may be
a byproduct).  Rather, the atoms or molecules of the gas inside a glass,
quartz, or translucent ceramic tube, are ionized by an electric current
through the gas or a radio frequency or microwave field in proximity to
the tube.  This results in the generation of light - usually either visible
or ultraviolet (UV).  The color depends on both the mixture of gasses or
other materials inside the tube as well as the pressure and type and amount
of the electric current or RF power.

Fluorescent lamps are a special class of gas discharge lamps where the
electric current produces mostly invisible UV light which is turned into
visible light by a special phosphor coating on the interior of the tube.
See the chapter: "Fluorescent Lamps, Ballasts, and Fixtures".

The remainder of this chapter discusses two classes of gas discharge lamps:
low pressure 'neon' tubes used in signs and displays and high intensity
discharge lamps used for very efficient area and directional lighting.  An
entire chapter is dedicated to "Fluorescent Lamps, Ballasts and Fixtures".

  13.2) Neon lights and signs

Neon technology has been around for many years providing the distinctive
bright glowing signs of commerce of all kinds before the use of colored
plastics became commonplace.

Neon tubes have electrodes sealed in at each end.  For use in signs, they
are formed using the glass blower's skill in the shape of letters, words,
or graphics.  Black paint is used to block off areas to be dark.  They are
evacuated, backfilled, heated (bombarded - usually by a discharge through
the tube at a very high current) to drive off any impurities, evacuated
and then backfilled with a variety of low pressure gasses.

Neon is the most widely known with its characteristic red-orange glow.
Neon may be combined with an internal phosphor coating (like a
fluorescent tube) to utilize neon's weak short-wave UV emissions.
Other gas fills may also be used as well as colored glass or coatings
for added flexibility in determining the tube's color.

  13.3) Power supplies for neon

Extremely high voltage power supplies are used to power neon signs.  In
the past, this was most often provided by a special current limited HV
line transformer called a neon sign or luminous tube transformer.  The
output is typically 6,000 to 15,000 VAC at 15 to 60 mA.  One such unit
can power 10s of feet of tubing.  This transformer acts as its own ballast
providing the high voltage needed for starting and limiting the running
current as well.  Warning: the output of these transformers can be lethal
since even the limited current availability is relatively high.

As with everything else, the newest neon sign power supplies use an
electronic AC-AC inverter greatly reducing the size and weight (and
presumably cost as well) of these power supplies by eliminating the
large heavy iron transformer.

Small neon lamps inside high-tech phones and such also use solid state
inverters to provide the more modest voltage required for these devices.

  13.4) Problems with neon

These fall into two categories:

1. Power supply - like fluorescent ballasts, the high voltage transformers
   can fail resulting in reduced (and inadequate) voltage or no power at all.
   Since they are already current limited, overheating may not result and
   any fuse or circuit breaker may be unaffected.  The use of a proper (for
   safety if nothing else) high voltage meter can easily identify a bad

2. Neon tubes - these may lose their ability to sustain a stable discharge
   over time as a result of contamination, gas leakage, or electrode damage
   (either from normal wear or due to excessive current).  Check for obvious
   damage such as a cracked tube or cracked seals around the electrodes or
   badly deteriorated electrodes.  A previously working tube that now will
   not strike or maintain a stable discharge on a known good transformer 
   will need to be replaced or rebuilt.

  13.5) High intensity discharge (HID) lamp technology

These have been used for a long time in street, stadium, and factory lighting.
More recently, smaller sizes have become available for home yard and crime
prevention applications.  Like other gas discharge lamps, these types
require s special fixture and ballast for each type and wattage.  Unlike
fluorescents, however, they also require a warmup period.

There are three popular types:

* High pressure mercury vapor lamps contain an internal arc tube made of
  quartz enclosed in an outer glass envelope.  A small amount of metallic
  (liquid) mercury is sealed in an argon gas fill inside the quartz tube.
  After the warmup period, the arc emits both visible and invisible (UV)
  light.  High pressure mercury vapor lamps (without color correction)
  produce a blue-white light directly from their discharge arc.  Phosphors
  similar to those used for fluorescent lamps can be used to give these a
  color closer to natural light.  (Without this color correction, people
  tend to look like cadavers).  Mercury vapor lamps have the longest life
  of this class of bulbs - 10,000 to 24,000 hours.  The technology was first
  introduced in 1934 and was the first of the commercially viable HID lamps.

* Metal halide lamps are constructed along similar lines to mercury vapor
  lamps.  However, in addition to the mercury and argon, various metal
  halides are included in the gas fill - usually combinations of sodium iodide
  and scandium iodide.  The use of these compounds increases the luminous
  efficiency and results in a more pleasing color balance than the raw arc
  of the mercury vapor lamp.  Thus, no phosphor is needed to produce a color
  approaching that of a cool white fluorescent lamp.

* High pressure sodium vapor lamps contain an internal arc tube made of
  a translucent ceramic material (a form of aluminum oxide known as
  "polcyrystalline alumina").  Glass and quartz cannot be used since they
  cannot maintain structural strength at the high temperatures (up to 1300
  degrees C) encountered here, and hot sodium chemically attacks quartz
  and glass.  Like other HID lamps, the arc tube is enclosed in an outer
  glass envelope.  A small amount of metallic (solid) sodium in addition
  to mercury is sealed in a xenon gas fill inside the ceramic arc tube.
  Some versions of this lamp use a neon-argon mixture instead of xenon.
  Basic operation is otherwise similar to mercury or metal halide lamps.
  High pressure sodium vapor lamps produce an orange-white light and have
  a luminous efficiency much higher than mercury or metal halide lamps.

Unlike fluorescent lamps, HID lamps will give full light output over a
wide range of temperatures.  This often makes HID lamps more suitable than
fluorescent lamps for outdoor use.

When cold, the metallic mercury or sodium in the arc tube is in its normal
state (liquid or solid) at room temperature.  During the starting process,
a low pressure discharge is established in the gases.  This produces very
little light but heats the metal contained inside the arc tube and gradually
vaporizes it.  As this happens, the pressure increases and light starts being
produced by the discharge through the high pressure metal vapor. A quite
noticeable transition period occurs when the light output increases
dramatically over a period of a minute or more.  The entire warmup process
may require up to 10 minutes, but typically takes 3 to 5 minutes.  A hot
lamp cannot be restarted until it has cooled since the voltage needed to
restrike the arc is too high for the normal AC line/ballast combination to

  13.6) Problems with high intensity discharge lamps

While HID lamps have a very long life compared to incandescents (up to
24,000 hours), they do fail.  The ballasts can also go bad.  In addition,
their light output falls off gradually as they age.  For some types, light
output may drop to half its original value towards the end of their life.

A lamp which is cycling - starting, warming up, then turning itself off -
is probably overheating due to a bad bulb or ballast.  A thermal protector
is probably shutting down the fixture to protect it or the arc is being
extinguished on its own.  However, make sure that it is not something
trivial like a photoelectric switch that is seeing the light from the lamp
reflected from a white wall or fence and turning the fixture off once the
(reflected) light intensity becomes great enough!

Sodium lamps often "cycle" when they have aged greatly.  The arc tube's
discolorations absorb light from the arc, causing the arc tube to overheat,
the sodium vapor pressure becomes excessive, and the arc cannot be maintained.
If a sodium lamp "cycles", the first suspect is an aging bulb which should be

If you have more than one fixture which uses **identical** bulbs, swapping
the bulbs should be the first test.  If the problem remains with the fixture,
then its ballast or other circuitry is probably bad.  Don't be tempted to swap
bulbs between non-identical fixtures even if they fit unless the bulb types
are the same.

Warning: do not operate an HID lamp if the outer glass envelope is cracked
or broken.  First, this is dangerous because the extremely hot arc tube can
quite literally explode with unfortunate consequences.  In addition, the
mercury arc produces substantial amounts of short wave UV which is extremely
hazardous to anything living.  The outer glass normally blocks most of
this from escaping.  Some lamps are actually designed with fusable links
that will open after some specified number of hours should air enter the
outer envelope.  Thus, an undetected breakage will result in the lamp dying
on its own relatively quickly.

Chapter 14) Motors 101

  14.1) Small motors in consumer electronic equipment

A large part of the functionality of modern appliances is based on the
use of motors of one form or another.  They are used to rotate, blow,
suck, sweep, spin, cut, grind, shred, saw, sand, drill, plane, time,
and control.

Motors come in all shapes and sizes but most found in small appliances
can be classified into 5 groups:

1. Universal motors - run on AC or DC, speed may be varied easily.  Quite
   efficient but use carbon brushes and may require maintenance.

2. Single phase induction motors - AC, fairly fixed speed except by switching,
   windings, very quiet.  Quite efficient and low maintenance.

3. Shaded pole induction motors - AC, somewhat fixed speed, very quiet, not
   very efficient and low maintenance.

4. Small permanent magnet DC motors - DC, variable or constant speed, often
   cheaply made, fairly quiet, prone to problems with metal brushes.

5. DC brushless motors - DC usually, somewhat variable or fixed speed, very
   quiet, low maintenance.

6. Synchronous timing motors - constant speed absolutely tied to power line.
   The long term accuracy of clocks based on the AC line exceed that of most
   quartz oscillator based time pieces since the ultimate reference is an
   atomic frequency standard.

Each has its advantages and disadvantages.  More than one type may be suitable
for any particular application.

  14.2) Identifying type of unknown motor

Determining the actual type of motor is the first step toward being
able to test to see if it is being powered properly or if there is
a fault in the motor itself.

Open frame motors in line operated appliances with a single coil off to
one side are almost always shaded pole induction motors.  To confirm, look
for the copper 'shading rings' embedded in the core.  There will usually
be either 1 or 2 pairs of these.  Their direction is determine by the
orientation of the stator frame (position of the shading rings).

For enclosed motors, first check to see if there are carbon brushes on
either side of a commutator made of multiple copper bars.  If so, this
is almost certainly a series wound 'universal' motor that will run on
AC or DC though some may be designed for DC operation only.

If there are no brushes, then it is likely a split phase induction or
synchronous motor.  If there is a capacitor connected to the motor, this
is probably used for starting and to increase torque when running.

Where there is a capacitor, it is likely that how this is wired to the
motor determines the direction of rotation - make sure you label the

Very small motors with enclosed gear reducers are usually of the synchronous
type running off the AC line.  Their direction of rotation is often set by
a mechanical one-way clutch mechanism inside the casing.

Motors used in battery operated tools and appliances will usually be of
the permanent magnet DC type similar to those found in toys and electronic
equipment like VCRs and CD players.  Most of these are quite small but there
are exceptions - some electric lawnmowers use large versions of this type of
motor, for example.  These will be almost totally sealed with a pair of
connections at one end.  Direction is determined by the polarity of the
DC applied to the motor.

For universal and DC permanent magnet motors, speed control may be accomplished
with an internal mechanical governor or electronic circuitry internal or
external to the motor.  On devices like blenders where a range of (useless)
speeds is required, there will be external switches selecting connections
to a tapped winding as well as possibly additional electronic circuitry.  The
'solid state' design so touted by the marketing blurb may be just a single
diode!  A similar approach may also be used to control the speed of certain
types of induction motors (e.g., ceiling fans) but most are essentially fixed
speed devices.

Once identified, refer to the appropriate section for your motor.

COLIN Electric Motor Service has a page with some Motor Connection Diagrams
for large motors that may be of some value (though more so if you have a few'
100 horsepower three-phase motors in your concrete processing plant!).

  14.3) Universal motors

The Universal motor is the most common type of high speed motor found
in appliances and portable line operated power tools.  Typical uses
include vacuum cleaners, floor polishers, electric drills, routers, and
sewing machines.  They are likely to be found anywhere medium power, high
speed, and/or variable speed control are required capabilities.  Note that
quiet operation is NOT a feature of these motors.  Therefore, they will
not often be found in electronic equipment.

Construction consists of a stationary set of coils and magnetic core called the
'stator' and a rotating set of coils and magnetic core called the 'armature'.
Incorporated on the armature is a rotating switch called a 'commutator'.
Connection to the armature is via carbon (or metal) contacts called 'brushes'
which are mounted on the frame of the motor and press against the commutator.
Technically, these are actually series wound DC motors but through the use of
steel laminated magnetic core material, will run on AC or DC - thus the name

Speed control of universal motors is easily achieved with thyristor
based controllers similar to light dimmers.  However, simply using a
light dimmer as a motor speed controller may not work due to the
inductive characteristics of universal motors.

Changing direction requires interchanging the two connections between the
stator and the armature.

This type of motor is found in blenders, food mixers, vacuum cleaners,
sewing machines, and many portable power tools.

  14.4) Problems with universal motors

These motors can fail in a number of ways:

* Open  windings - this may result in a bad spot, a totally dead motor,
  lack of power, or excessive sparking. 

* Shorted windings - this may result in excessive current, severe sparking,
  reduced speed and power, and overheating.  The thermal protector, fuse,
  or circuit breaker may trip.  Continuing to run such a motor may result
  in a meltdown or burned coils and insulation - i.e., a burned out motor.

* Worn carbon brushes - while these usually last for the life of the
  appliance, this is not always the case.  The result could be erratic
  or sluggish operation, excessive sparking, or even damage to the

* Dry/worn bearings - this may result in a tight or frozen motor or a motor
  shaft with excessive runout.  The result may be a spine tingling squeal
  during operation and/or reduced speed and power, and overheating.  Running
  such a motor may eventually lead to burnout due to overheating from the
  increased load.

  14.5) Testing of universal motors

Test the field coils for continuity with an ohmmeter.  An open winding is
bad and will require replacement of the entire stator assembly unless the
break can be located.  Compare the resistance of the two windings - they
should be nearly equal.  If they are not, a short in one of the windings
is likely.  Again, replacement will be necessary.

Also test for a short to the frame - this should read infinity.  If lower than
1 M or so, the motor will need to be replaced unless you can locate the fault.

An open or shorted armature winding may result in a 'bad spot' - a position
at which the motor may get stuck.  Rotate the motor by hand a quarter turn and
try it again.  If it runs now either for a fraction of a turn or behaves
normally, then replacement will probably be needed since it will get stuck
at the same point at some point in the future.  Check it with an ohmmeter.
There should be a periodic variation in resistance as the rotor is turned
having several cycles per revolution determined by the number of commutator
segments used.  Any extremely low reading may indicate a shorted winding.
Any erratic readings may indicate the need for brush replacement or cleaning.
An unusually high reading may indicate an open winding or dirty commutator.
Cleaning may help a motor with an open or short or dead spot.

A motor can be tested for basic functionality by disconnecting it from the
appliance circuit and running it directly from the AC line (assuming it is
intended for 115 VAC operation - check to be sure).

CAUTION: series wound motors can overspeed if run without a load of any kind
and spectacular failure may result due to centrifugal disassembly of the
armature due to excess G forces.  In other words, the rotor explodes.  This is
unlikely with these small motors but running only with the normal load
attached is a generally prudent idea.

  14.6) About commutators and brushes in universal motors

A commutator is essentially a rotating switch which routes power to the
appropriate windings on the armature so that the interaction of the fixed
(stator) and rotating (armature) magnetic fields always results in a
rotational torque.  Power is transferred to the commutator using carbon
brushes in most motors of this type.  The carbon is actually in the form
of graphite which is very slippery as well.  Despite that fact that graphite
is a relatively soft material, a thin layer of graphite is worn off almost
immediately as the motor is started for the first time and coats the
commutator.  After this, there is virtually no wear and a typical set of
carbon brushes can last thousands of hours - usually for the life of the
appliance or power tool.

A spring presses the brush against the rotating commutator to assure good
electrical contact at all times.  A flexible copper braid is often embedded
in the graphite block to provide a low resistance path for the electric
current.  However, small motors may just depend on the mounting or pressure
spring to provide a low enough resistance.

The typical universal motor will have between 3 and 12 armature windings
which usually means a similar number of commutator segments.  The segments
are copper strips secured in a non-conductive mounting.  There are supposed
to be insulating gaps between the strips which should undercut the copper.
With long use, the copper may wear or crud may build up to the point that
the gaps between the copper segments are no longer undercut.  If this
happens, their insulating properties will largely be lost resulting in an
unhappy motor.  There may be excessive sparking, overheating, a burning
smell, loss of power, or other symptoms.

Whenever checking a motor with a commutator, inspect to determine if the
commutator is in good condition - smooth, clean, and adequately undercut.
Use a narrow strip of wood or cardboard to clean out the gaps assuming
they are still present.  For larger motors, a hacksaw blade can be used
to provide additional undercutting if needed though this will be tough
with very small ones.  Don't go too far as the strength of the commutator's
mounting will be reduced.  About 1/32 to 1/16 inch should do it.  If the
copper is pitted or worn unevenly, use some extra fine sandpaper (600 grit,
not emery cloth or steel wool which may leave conductive particles behind)
against the commutator to smooth it while rotating the armature by hand.

Since the carbon brushes transmit power to the rotating armature,
they must be long enough and have enough spring force behind them to
provide adequate and consistent contact.  If they are too short, they
may be unstable in their holders as well - even to the point of being
ripped from the holder by the commutator causing additional damage.

Inspect the carbon brushes for wear and free movement within their holders.
Take care not to interchange the two brushes or even rotate them from their
original orientation as the motor may then require a break-in period and
additional brush wear and significant sparking may occur during this time.
Clean the brushes and holders and/or replace the brushes if they are broken
or excessively worn.

  14.7) Repairing small universal motors

Too bad that the Sears lifetime warranty only applies to hand (non-power)
tools, huh?

Which part of the motor is bad?  The armature or stator?  How do you 
know? (A smelly charred mess would probably be a reasonable answer).

Rewinding a motor is probably going to way too expensive for a small
appliance or power tool.  Finding a replacement may be possible since
those sizes and mounting configurations were and are very common.

However, I have, for example, replaced cheap sleeve bearings with ball
bearings on a couple of Craftsman power drills.  They run a whole lot
smoother and quieter.  The next model up used ball bearings and shared
the same mounting as the cheaper sleeve bearings so substitution was

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Written by Samuel M. Goldwasser. | [mailto]. The most recent version is available on the WWW server http://www.repairfaq.org/ [Copyright] [Disclaimer]