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


  5.16) Lubrication of appliances and electronic equipment

The short recommendation is: Don't add any oil or grease unless you are
positively sure it is needed.  Most parts are lubricated at the factory and do
not need any further lubrication over their lifetime.  Too much lubrication is
worse then too little.  It is easy to add a drop of oil but difficult and time
consuming to restore a tape deck that has taken a swim.

NEVER, ever, use WD40!  WD40 is not a good lubricant despite the claims on the
label.  Legend has it that the WD stands for Water Displacer - which is one of
the functions of WD40 when used to coat tools for rust prevention.  WD40 is
much too thin to do any good as a general lubricant and will quickly collect
dirt and dry up.  It is also quite flammable and a pretty good solvent - there
is no telling what will be affected by this.

A light machine oil like electric motor or sewing machine oil should be
used for gear or wheel shafts.  A plastic safe grease like silicone grease
or Molylube is suitable for gears, cams, or mechanical (piano key) type
mode selectors.  Never use oil or grease on electrical contacts.

One should also NOT use a detergent oil.  This includes most automotive
engine oils which also have multiple additives which are not needed and are
undesirable for non-internal combustion engine applications.

3-In-One(tm) isn't too bad if that is all you have on hand and the future of
the universe depends on your fan running smoothly.  However, for things that
don't get a lot of use, it may gum up over time.  I don't know whether it
actually decomposes or just the lighter fractions (of the 3) evaporate.

Unless the unit was not properly lubricated at the factory (which is quite
possible), don't add any unless your inspection reveals the specific need.
Sometimes you will find a dry bearing, motor, lever, or gear shaft.  If
possible, disassemble and clean out the old lubricant before adding fresh
oil or grease.

Note that in most cases, oil is for plain bearings (not ball or roller)
and pivots while grease is used on sliding parts and gear teeth.

In general, do not lubricate anything unless you know there is a need.
Never 'shotgun' a problem by lubricating everything in sight!  You might
as well literally use a shotgun on the equipment!

  5.17) Common appliance problems

Despite the wide variety of appliances and uses to which they are put,
the vast majority of problems are going to be covered in the following
short list:

1. Broken wiring inside cordset - internal breaks in the conductors of
   cordsets or other connecting cords caused by flexing, pulling, or
   other long term abuse.  This is one of the most common problem with
   vacuum cleaners which tend to be dragged around by their tails.

   Testing: If the problem is intermittent, (or even if it is not), plug
   the appliance in and turn it on.  Then try bending or pushing the wire
   toward the plug or appliance connector end to see if you can make the
   internal conductors touch at least momentarily.  Ii the cordset is
   removable, test between ends with a continuity checker or multimeter
   on the low ohms scale.  If it is not detachable, open the appliance to
   perform this test.

2. Bad internal connections - broken wires, corroded or loosened terminals.
   Wires may break from vibration, corrosion, poor manufacturing, as
   well as thermal fatigue.  The break may be in a heating element or
   other subassembly.  In many cases, failure will be total as in
   when one of the AC line connections falls off.  At other times,
   operation will be intermittent or erratic - or parts of the appliance
   will not function.  For example, with a blow dryer, the heating element
   could open up but the fan may continue to run properly.

   Testing: In many cases, a visual inspection with some careful flexing
   and prodding will reveal the location of the bad connection.  If it is
   an intermittent, this may need to be done with a well insulated stick
   while the appliance is on and running (or attempting to run).  When
   all else fails, the use of a continuity checker or multimeter on the
   low ohms scale can identify broken connections which are not obviously
   wires visibly broken in two.  For testing heating elements, use the
   multimeter as a continuity checker may not be sensitive enough since
   the element normally has some resistance.

3. Short circuits.  While much less frequent than broken or intermittent
   connections, two wires touching or contacting the metal case of an
   appliance happens all too often.  Partially, this is due to the shoddy
   manufacturing quality of many small appliances like toaster ovens.  These
   also have metal (mostly) cabinets and many metal interior parts with
   sharp edges which can readily eat through wire insulation due to repeated
   vibrations, heating and cooling cycles, and the like.  Many appliances
   are apparently designed by engineers (this is being generous) who do not
   have any idea of how to build or repair them.  Thus, final assembly, for
   example, must sometimes be done blind - the wires get stuffed in and covers
   fastened - which may end up nicking or pinching wires between sharp metal
   parts.  The appliance passes the final inspection and tests but fails down
   the road.

   A short circuit may develop with no operational problems - but the case
   of the appliance will be electrically 'hot'.  This is a dangerous situation.
   Large appliances with 3 wire plugs - plugged into a properly grounded 3 wire
   circuit - would then blow a fuse or trip a circuit breaker.  However, small
   appliances like toaster, broilers, irons, etc., have two wire plugs and
   will just set there with a live cabinet.

   Testing: Visually inspect for bare wires or wires with frayed or worn
   insulation touching metal parts, terminals they should not be connected
   to, or other wires.  Use a multimeter on the high ohms scale to check
   between both prongs of the AC plug and any exposed metal parts.  Try all
   positions of any power or selector switches.  Any resistance measurement
   less than 100K ohms or so is cause for concern - and further checking.
   Also test between internal terminals and wires that should not be connected

   Too many people like to blame everything from blown light bulbs to
   strange noises on short circuits.  A 'slight', slow, or marginal short
   circuit is extremely rare.  Most short circuits in electrical wiring
   between live and neutral or ground (as opposed to inside appliances
   where other paths are possible) will blow a fuse or trip a breaker.  Bad
   connections (grounds, neutral, live), on the other hand, are much much
   more common.

4. Worn, dirty, or broken switches or thermostat contacts.  These will
   result in erratic or no action when the switch is flipped or thermostat
   knob is turned.  In many cases, the part will feel bad - it won't have
   that 'click' it had when new or may be hard to turn or flip.  Often,
   however, operation will just be erratic - jiggling the switch or knob
   will make the motor or light go on or off, for example.

   Testing: Where there is a changed feel to the switch or thermostat with
   an associated operational problem, there is little doubt that the part
   is bad and must be replaced.  Where this is not the case, label the
   connections to the switch or thermostat and then remove the wires.  Use
   the continuity checker or ohmmeter across each set of contacts.  They
   should be 0 ohms or open depending on the position of the switch or knob
   and nothing in between.  In most cases, you should be able to obtain
   both readings.  The exception is with respect to thermostats where room
   temperature is off one end of their range.  Inability to make the contacts
   open or close (except as noted above) or erratic intermediate resistances
   which are affected by tapping or jiggling are a sure sign of a bad set of

5. Gummed up lubrication, or worn or dry bearings.  Most modern appliances
   with motors are supposedly lubricated for life.  Don't believe it!  Often,
   due to environmental conditions (dust, dirt, humidity) or just poor quality
   control during manufacture (they forgot the oil), a motor or fan bearing
   will gum up or become dry resulting in sluggish and/or noisy operation
   and overheating.  In extreme cases, the bearing may seize resulting in
   a totally stopped motor.  If not detected, this may result in a blown
   fuse (at the least) and possibly a burnt out motor from the overheating.

   Testing: If the appliance does not run but there is a hum (AC line
   operated appliances) or runs sluggishly or with less power than you 
   recall when new, lubrication problems are likely.  With the appliance
   unplugged, check for free rotation of the motor(s).  In general, the
   shaft sticking out of the motor itself should turn freely with very
   little resistance.  If it is difficult to turn, the motor bearings
   themselves may need attention or the mechanism attached to the motor
   may be filled with crud.  In most cases, a thorough cleaning to remove
   all the old dried up and contaminated oil or grease followed by relubing
   with similar oil or grease as appropriate will return the appliance to
   good health.  Don't skimp on the disassembly - total cleaning will be
   best.  Even the motor should be carefully removed and broken down to
   its component parts - end plates, rotor, stator, brushes (if any) in
   order to properly clean and lubricate its bearings.  See the appropriate
   section of the chapter: "Motors 101" for the motor type in your appliance.

6. Broken or worn drive belts or gears - rotating parts do not rotate
   or turn slowly or with little power even through the motor is revving
   its little head off.  When the brush drive belt in an upright vacuum
   cleaner breaks, the results are obvious and the broken belt often falls
   to the ground (to be eaten by the dog or mistaken for a mouse tail - Eeek!)
   However, there are often other belts inside appliances which will result
   in less obvious consequences when they loosen with age or fail completely.

   Testing: Except for the case of a vacuum cleaner where the belt is readily
   accessible, open the appliance (unplugged!).  A good rubber belt will be
   perfectly elastic and will return to its relaxed length instantly when
   stretched by 25 percent and let go.  It will not be cracked, shiny, hard,
   or brittle.  A V-type belt should be dry (no oil coating), undamaged (not
   cracked, brittle, or frayed), and tight (it should deflect 1/4" to 1/2"
   when pressed firmly halfway between the pulleys).

   Sometimes all that is needed is a thorough cleaning with soap and water
   to remove accumulated oil or grease.  However, replacement will be required
   for most of these symptoms.  Belts are readily available and an exact
   match is rarely essential.

7. Broken parts - plastic or metal castings, linkages, washers, and other
   'doodads' are often not constructed quite the way they used to be.  When
   any of these fail, they can bring a complicated appliance to its knees.
   Failure may be caused by normal wear and tear, improper use (you tried
   to vacuum nuts and bolts just like on TV), accidents (why was your 3
   year old using the toaster oven as a step stool?), or shoddy manufacturing.

   Testing: In many cases, the problem will be obvious.  Where it is not,
   some careful detective work - putting the various mechanisms through
   their paces - should reveal what is not functioning.  Although replacement
   parts may be available, you can be sure that their cost will be excessive
   and improvisation may ultimately be the best approach to repair.  See
   the section: "Fil's tips on improvised parts repair".

8. Insect damage.  Many appliance make inviting homes for all sort of multi-
   legged creatures.  Evidence of their visits or extended stays will be
   obvious including frayed insulation, short circuits caused by bodily
   fluids or entire bodies, remains of food and droppings.  Even the smallest
   ventilation hole can be a front door.

   The result may be any of the items listed in (1) to (7) above.  Once the
   actual contamination has been removed and the area cleaned thoroughly,
   inspect for damage and repair as needed.  If the appliance failed while
   powered, you may also have damage to wiring or electronic components due
   to any short circuits that were created by the intruders' activities.

Chapter 6) Types of Parts Found in Small Appliances

  6.1) So many, so few

While there are an almost unlimited variety of small appliances and power
tools, they are nearly all constructed from under two dozen basic types
of parts.  And, even with these, there is a lot of overlap.

The following types of parts are found in line powered appliances:

        * Cordsets - wire and plug.
        * Internal wiring - cables and connectors.
        * Switches - power, mode, or speed selection.
        * Relays - electrically activated switches for power or control.
        * Electrical overload protection devices - fuses and circuit breakers.
        * Thermal protection devices - thermal fuses and thermal switches.
        * Controls 1 - adjustable thermostats and humidistats.
        * Controls 2 - rheostats and potentiometers.
        * Interlocks - prevent operation with case or door open.
        * Light bulbs - incandescent and fluorescent.
        * Indicators - incandescent or neon light bulbs or LEDs.
        * Heating elements - NiChrome coils or ribbon, Calrod, Quartz.
        * Solenoids - small and large.
        * Small electronic components - resistors, capacitors, diodes.
        * Motors - universal, induction, DC, timing.
        * Fans and Blowers - bladed or centrifugal.
        * Bearings and bushings.
        * Mechanical controllers - timing motors and cam switches.
        * Electronic controllers - simple delay or microprocessor based.

Battery and AC adapter powered appliance use most of the same types of
parts but they tend to be smaller and lower power than their line powered
counterparts.  For example, motors in line powered devices tend to be
larger, more powerful, and of different design (universal or induction
compared to permanent magnet DC type).  So, we add the following:

        * Batteries - Alkaline, Lithium, Nickel-Cadmium, Lead-acid.
        * AC adapters and chargers - wall 'warts' with AC or DC outputs.

The only major category of devices that these parts do not cover are gas
discharge lamps and lighting fixtures (fluorescent, neon, mercury, and
sodium), which we will discuss in a separate chapters.

  6.2) Cordsets - wire and plug

A 'cordset' is a combination of the cord consisting of 2 or 3 insulated wires
and a plug with 2 or 3 prongs.  Cord length varies from 12 inches (or less)
for some appliances like toasters to 25 feet or more for vacuum cleaners.
Most common length is 6-8 feet.  The size of the wire and type of insulation
also are important in matching a replacement cordset to an appliance.

Most plug-in appliances in the U.S. will have one of 3 types of line cord/plug

1. Non-polarized 2 prong.  The 2 prongs are of equal width so the plug
   may be inserted in either direction.  These are almost universal
   on older appliances but may be found on modern appliances as well 
   which are double insulated or where polarity does not matter.  (Note:
   it **must** not matter for user safety in any case.  The only time it can
   matter otherwise is with respect to (1) possible RFI (Radio Frequency
   Interference) generation or (2) service safety (this would put the
   center contact of a light bulb socket or internal switch and fuse on
   the Hot wire).

2. Polarized 2 prong.  The prong that is supposed to be plugged into
   the Neutral slot of the outlet is wider.  All outlets since sometime
   around the 1950s (???) have been constructed to accept polarized plugs
   only one way.  While no appliance should ever be designed where the
   way it is plugged in can result in a user safety hazard, a lamp socket
   where the shell - the screw thread part - is plugged into Neutral is
   less hazardous when changing a light bulb.  In addition, when servicing
   a small appliance with the cover removed, the Hot wire with a polarized
   plug should go to the switch and fuse and thus most of the circuitry will
   be disconnected with the switch off or fuse pulled.

3. Grounded 3 prong.  In addition to Hot and Neutral, a third grounding
   prong is provided to connect the case of the equipment to safety Ground.
   This provides added protection should internal wiring accidentally short
   to a user accessible metal cabinet or control.  In this situation, the
   short circuit will (or is supposed to) blow a fuse or trip a circuit
   breaker or GFCI rather than present a shock hazard.  DO NOT just cut
   off the third prong if your outlet does not have a hole for it.  Have
   the outlet replaced with a properly grounded one (which may require
   pulling a new wire from the service panel).  As a short term solution,
   the use of a '3 to 2' prong adapter is acceptable IF AND ONLY IF the
   outlet box is securely connected to safety Ground already (BX or Romex
   cable with ground).  Grounding also is essential for surge suppressors
   to operate properly (to the extent that they ever do) and may reduce
   RFI susceptibility and emissions if line filters are included (as with
   computer equipment and consumer electronics).  Power conditioners require
   the Ground connection for line filtering as well.

Each of these may be light duty (less than 5 Amps or 600 Watts), medium
duty (8 A or 1000 W) or heavy duty (up to 15 A or 1800 W).  The rating is
usually required to be stamped on the cord itself or on a label attached
to the cord.  Thickness of the cord is not a reliable indication of its
power rating!  (Note: U.S. 115 VAC 15 amp circuits are assumed throughout
this document unless otherwise noted.)

Light duty cordsets are acceptable for most appliances without high power
heating elements or heavy duty electric motors.  These include table lamps,
TVs, VCRs, stereo components, computers, dot matrix and inkjet printers,
thermal fax machines, monitors, fans, can openers, etc.  Electric blankets,
heating pads, electric brooms, and food mixers are also low power and light
duty cordsets are acceptable.  The internal wires used is #18 AWG which is
the minimum acceptable wire size (highest AWG number) for any AC line powered

Medium or heavy duty cordsets are REQUIRED for heating appliances like
electric heaters (both radiant and convection), toasters, broilers, steam and
dry irons, coffee makers and electric kettles, microwave and convection ovens,
laser printers, photocopiers, Xerographic based fax machines, canister and
upright vacuum cleaners and shop vacs, floor polishers, many portable and
most stationary power tools.  The internal wires used will be #16 AWG (medium
duty) or #14 AWG (heavy duty).

For replacement, always check the nameplate amps or wattage rating and use
a cordset which has a capacity at least equal to this.  The use of an
inadequate cordset represents a serious fire hazard.

Three prong grounded cordsets are required for most computer equipment,
heavy appliances, and anything which is not double insulated and has metal
parts that may be touched in normal operation (i.e., without disassembly).

The individual wires in all cordsets except for unpolarized types (e.g., lamp
cord) will be identified in some way.  For sheathed cables, color coding is
used.   Generally, in keeping with the NEC (Code), black will be Hot, white
will be Neutral, and green will be Safety Ground.  You may also find brown for
Hot, blue for Neutral, and green with a yellow stripe for Safety Ground.  This
is used internationally and is quite common for the cordsets of appliances and
electronic equipment.

For zip cord with a polarized plug, one of the wires will be tagged with with
a colored thread or a ridge on the outer insulation to indicate which is the
Neutral wire.  For unpolarized types like lamp cord, no identification is
needed (though there still may be some) as the wires and prongs of the plug are

In general, when replacement is needed, use the same configuration and
length and a heavy duty type if the original was heavy duty.  Substituting
a heavy duty cordset for a light duty one is acceptable as long as the
additional stiffness is acceptable in terms of convenience.  A shorter
cord can usually be used if desired.  In most cases, a longer cord (within
reason) can be substituted as well.  However, performance of heavy duty
high current high wattage appliances may suffer if a really long cord (or
extension cord) is used voltage drop from the wire resistance.  For a modest
increase in length, use the next larger wire size (heavy duty instead of
medium duty, #14 instead of #16, for example).

Before disconnecting the old cord, label connections or make a diagram and
then match the color code or other wire identifying information.  In all cases,
it is best to confirm your final wiring with a continuity tester or multimeter
on the low ohms scale.  Mistakes on your part or the manufacturer of the new
cord are not unheard of!

Common problems: internal wiring conductors broken at flex points (appliance
or plug).  With yard tools, cutting the entire cord is common.  The connections
at the plug may corrode as well resulting in heating or a broken connection.

Testing: Appliance cordsets can always be tested with a continuity checker or
multimeter on a the low ohms scale.

* Squeeze, press, spindle, fold, mutilate the cord particularly at both ends
  as while testing to locate intermittent problems.

* If you are too lazy to open the appliance (or this requires the removal of
  29 screws), an induction type of tester such as used to locate breaks in
  Christmas tree light strings can be used to confirm continuity by plugging
  the cord in both ways and checked along its length to see if a point of
  discontinuity can be located.

  (From: Brian Symons (brians@mackay.net.au)).

  A permanent bench setup with a pair of outlets (one wired with reverse
  polarity marked: FOR TESTING ONLY) can be provided to facilitate connecting
  to either of the wires of the cordset when using an induction type tester.

Note: broken wires inside the cordset at either the plug or appliance end
are among the most common causes of a dead vacuum cleaner due to abuse
it gets - being tugged from the outlet, vacuum being dragged around by
the cord, etc.  Many other types of appliances suffer the same fate.
Therefore, checking the cord and plug should be the first step in
troubleshooting any dead appliance.

If the cord is broken at the plug end, the easiest thing to do is to
replace just the plug.  A wide variety of replacement plugs are available
of three basic types: clamp-on/insulation piercing, screw terminals,
and wire compression.

Clamp-on/insulation piercing plugs are installed as follows:  First, the
cord is cleanly cut but not stripped and inserted into the body of the
plug.  A lid or clamping bar is then closed which internally pierces the
insulation and makes contact with the prongs.  When used with the proper
size wire, these are fairly reliable for light duty use - table lamps
and other low power appliances.  However, they can lead to problems of
intermittent or bad connections if the wire insulation thickness does not
precisely match what the plug expects.

Plugs with screw terminals make a much more secure robust connections but
require a bit more time and care in assembly to assure a proper connection
and avoid stray wire strands causing short circuits or sticking out and
representing a shock hazard.  Tightly twist the strands of the stripped
wire together before wrapping around the screw in a clockwise direction
before tightening.  Don't forget to install the fiber insulator that is
usually supplied with the plug.

The best plugs have wire clamp terminals.  The stripped end of the wire
is inserted into a hole and a screw is tightened to clamp the wire in
place.  Usually, a molded plastic cover is then screwed over this assembly
and includes a strain relief as well.  These are nearly foolproof and
consequently are used in the most demanding industrial and medical
applications.  They are, not surprisingly, also typically the most

Where damage is present at the appliance end of the cord, it may be possible
to just cut off the bad portion and reinstall what remains inside of the
appliance.  As long as this is long enough and a means can be provided for
adequate strain relief, this is an acceptable alternative to replacement of
the entire cordset.

  6.3) Appliance cord gets hot

This applies to all high current appliances, not just space heaters though
these are most likely to be afflicted since they are likely to be run for
extended periods of time.

Of course, if the problem is with an *extension* cord, then either it is
overloaded or defective.  In either case, the solution should be obvious.

Some cords will run warm just by design (or cheapness in design using
undersized conductors).

However, if it is gets hot during use, this is a potential fire hazard.

If it is hot mainly at the plug end - get a heavy duty replacement plug - one
designed for high current appliances using screw terminals - at a hardware
store, home center, or electrical supply house.  Cut the cord back a couple
of inches.

If the entire cord gets warm, this is not unusual with a heater.  If it
gets hot, the entire cord should be replaced.  Sometimes with really old
appliance, the copper wires in the cord oxidize even through the rubber
insulation reducing their cross section and increasing resistance.  This
leads to excessive power dissipation in the cord.  Replacement *heavy duty*
cordsets are readily available.

  6.4) Extension cords

We treat extension cords too casually - abusing them and using underrated
extension cords with heavy duty appliances.  Both of these are serious
fire and shock hazards.  In addition, the use of a long inadequate
extension will result in reduced voltage due to resistive losses at the
far end.  The appliance may not work at full capacity and in some cases
may even be damaged by this reduced voltage.

Extension cord rules of use:

1. The capacity must be at least equal to the SUM of the wattages or amperages
   of all the appliances plugged in at the far end.  Larger is fine as well
   and is desirable for long extensions.  Check the rating marked on the cord
   or a label attached to the cord.  Thickness of the outside of the cord is
   not a reliable indication of power rating.

2. Use a type which is the most restrictive of any appliances that will be
   plugged in (e.g., 3 prong if any are of this type, 2 prong polarized
   otherwise unless your outlets are non-polarized (old dwellings).

3. Use only as long an extension as required.  For very long runs, use
   a higher capacity extension even if the power requirements are modest.

4. NEVER run extensions under carpeting as damage is likely and this will
   go undetected.  Never run extensions inside walls.  Add new outlets where
   needed with properly installed building wire (Romex).  This must be done
   in such a way that it meets the National Electric Code (NEC) in your area.
   It may need to be inspected if for no other reason than to guarantee that
   your homeowner's insurance won't give you a hard time should any 'problems'
   arise.  Surface mount outlets and conduit are available to extend the reach
   of existing outlets with minimal construction if adding new ones is
   difficult or too costly.

5. Don't use heavy duty extensions as a long term solution if possible.
   Similarly, don't use extensions with 'octopus' connections - install
   an outlet strip.

Extension cords of any type, capacity, and length can be easily constructed
from components and wire sold at most hardware stores and home centers.  This
is rarely economical for light duty polarized types as these are readily
available and very inexpensive.  However, for heavy duty 3 prong extensions,
a custom constructed one is likely to save money especially if an unusual
length is required.  Making up a heavy duty extension with a 'quad' electrical
box with a pair of 15 amp duplex outlets is a very rugged convenient
alternative to a simple 3 prong socket.

Common problems: internal wiring conductors broken at flex points (socket
or plug).  With yard tools, cutting the entire cord is common.  The connections
at the plug may corrode as well resulting in heating or a bad or intermittent

Testing: Extension cords can always be tested with a continuity checker or
multimeter on a the low ohms scale.

  6.5) Determining the location of a break in an extension cord

This isn't worth the time it would take to describe for a $.99 6 foot K-Mart
special but it might make sense for a 100 foot heavy duty outdoor type.  If
the problem is near one end, a couple of feet can be cut off and a new plug
or socket installed.  If more towards the middle, the wires can be cut and
spliced or two smaller cords could be made from the pieces.

But, how do you locate the break?

* Use a Time Domain Reflectometer (TDR).  Oops, don't have one?  And, you
  probably don't even know what this means!  (Basically, a TDR sends a pulse
  down a wire and measures how long it takes for a reflected pulse to return
  from any discontinuities.  The delay is a measure of distance.)  Don't
  worry, there are alternatives :-).

* If there is no obvious damage - you didn't attempt to mow the cord by
  accident - the most likely location is at the end where the plug of socket
  strain relief joins the wire.  Squeezing, squishing, pushing, etc., with the
  cord plugged into a live outlet and lamp or radio plugged into the other end
  may reveal the location by a momentary flash or blast of sound.  

* Try a binary search with a probe attached to a straight pin.  This works
  best with a cord where the wires are easily located - not the round double
  insulated type.  Attach one probe of your multimeter to the prong of the
  plug attached to the broken wire.  Start at the middle with your pin probe.
  If there is continuity move half the distance to the far end.  If it is
  open, move half the distance toward near end.  Then 1/4, 1/8, and so forth.
  It won't take long to located the break this way.  Of course, there will be
  pin holes in the insulation so this is not recommeded for outdoor extension
  cords unless the holes are sealed.

* You may be able to use one of those gadgets for testing Christmas Tree light
  sets - these inexpensive devices sense the AC field in proximity to its
  probe.  Plug the cord in so that the Hot of your AC line is connected to one
  of the wires you know is broken (from testing with an ohmmeter) and run the
  device along the cord until the light changes intensity.

  This also works for appliance cords where you are too lazy to go inside to
  check continuity.  You may need to try both wires in the cord to locate the
  broken one.

* If you have some real test equipment (but not a TDR!) attach the output of
  a frequency generator to the prong of the plug for the wire you know is
  broken.  Use an oscilloscope as a sensor - run the probe along the cord
  until the detected signal abruptly drops in intensity.

  An AM or multiband radio may also be suitable as a detector.

  (From: Asimov (Asimov@juxta.mn.pubnix.ten)).

  Try a capacitance ratio method. Simply measure the capacitance between the
  wires at both ends. The break should be at approximately the same distance
  ratio as that of the two measured capacitances.

  6.6) Internal wiring - cables and connectors

Wiring isn't super glamorous but represents the essential network of roads
that interconnect all of the appliance's internal parts and links it to the
outside world.

Inside the appliance, individual wires (often multicolored to help identify
function) or cables (groups of wires combined together in a single sheath
or bundle) route power and control signals to the various components.  Most
are insulated with plastic or rubber coverings but occasionally you will
find bare, tinned (solder coated), or plated copper wires.  In high temperature
appliances like space heaters and toasters, the insulation (if present) will
be asbestos (older) or fiberglass.  (Rigid uninsulated wires are also commonly
found in such applications.)  Particles flaking off from either of these
materials are a health hazard if you come in contact, inhale, or ingest them.
They are also quite fragile and susceptible to damage which may compromise
their insulating properties so take care to avoid excessive flexing or
repositioning of wires with this type of insulation.  Fiberglass insulation
is generally loose fitting and looks like woven fabric.  Asbestos is light
colored, soft, and powdery.

Color coding will often be used to make keeping track of the wires easier
and to indicate function.  However, there is no standard except for the
input AC line.  Generally, black will be used for Hot, white will be used
for Neutral, and green or uninsulated wire will be used for Safety Ground.
While this is part of the NEC (Code) for electrical wiring (in the U.S.), it
is not always followed inside appliances.  You may also find brown for Hot,
blue for Neutral, and green with a yellow stripe for Safety Ground.  This
is used internationally and is quite common for the cordsets of appliances
and electronic equipment.

Where a non-polarized plug (cordset) is used, either AC wire can be Hot and
both wires will typically (but not always) be the same color.

Other colors may be used for switched Hot (e.g., red), thermostat control,
motor start, solenoid 1, etc.  Various combinations of colored stripes may
be used as well.  Unfortunately, in some cases, you will find that all the
wiring is the same color and tracing the circuit becomes a pain in the

Where multiple wires need to go from point A to point B along the same path,
they will often be combined into a single cable which is bundled using nylon
or cloth tie-wraps or run inside a single large flexible plastic sheath.  For
electronic interconnects and low voltage control and signal wiring, molded
flat cables are common (like those for the cables to the diskette and hard
drives of your PC).  These are quite reliable and can be manufactured at low
cost by fully automatic machines.

The thickness of the insulation of a wire or cable is not a reliable indication
of its capacity or voltage rating.  A fat wire may actually have a very skinny
central conductor and vice-versa.  In some cases, the wire conductor size and
voltage rating will be printed on the insulation but this not that common.
If replacement is needed, this information will be essential.  However, the
ampacity (maximum current) can be determined from the size of the metal
conductor and for any of the line powered appliances discussed in this
document, wire with a 600 V rating should be more than adequate.

The type of insulation is critical in appliances that generate heat - including
table lamps and other lighting fixtures.  There is special high temperature
insulated wire (fixture wire) which should be used when replacement is needed.
For heating appliances like toasters, hair dryers, and deep friers, fiberglass
or high temperature silicone based rubber insulated wire or insulating sleeves
must be used should the original wiring need replacement.  An appliance repair
motor rebuilding shop would be the most likely source - common electronics
distributors may not carry this stuff (especially if you only need a couple

Connections between individual wires and between individual wires and other
components are most often made by crimp or screw terminals, welding, or
press-in contacts.  For cables, actual multipin and socket connectors may
be used.

Common problems: internal wiring conductors broken, corroded, or deteriorated
due to heat or moisture.  Dirty, corroded, weakened, or damaged connector
contacts are common requiring cleaning and reseating or replacement.  Damage
to insulation from vibration, heat, movement, or even improper manufacture or
design is also possible.  Careless reassembly during a previous repair could
result in pinched broken wires or insulation as well as short circuits between
wires, or wiring and sharp sheet metal parts.

Testing: Inspect for obvious breaks or wires that have pulled out of their
terminations.  Integrity of wiring can be determined with a continuity checker
or multimeter on a the low ohms scale.  Flexing and wiggling wires especially
at connections while observing the meter will identify intermittents.

  6.7) Switches - power, mode, or speed selection

Most appliances have at least one switch to turn the appliance on and off.
In some cases, this may be combined with a thermostat or other control.
However, switches serve a variety of functions as well.

* Power - Nearly all appliances that run on AC directly (no wall transformer)
  provide some means of completely disconnecting at least one side of the AC
  line when not in use.  This may be a rocker, slide, push-push, trigger,
  toggle, rotary, or other separate switch.  It may also be combined with
  another function like a speed control or thermostat.

* Selector, mode, function - these switches may be used to determine speed
  in a mixer or blender, or the heat or air-only setting on a blow-dryer,
  for example.

* Internal (not user accessible) - these perform functions like detecting
  the position of a mechanism (e.g., limit switch), cam operated timing,
  and other similar operations that are not directly performed by the user.

In all cases, the function of a switch is the same - to physically make (on)
or break (off) the circuit or connect one signal to another.

* The most common type of switches have a set of metallic contacts (special
  materials to resist arcing and corrosion) which are brought together as a
  result of mechanical motion of a rocker, lever, etc. to complete the circuit
  There is usually some sort of snap action to assure rapid make and break of
  the circuit to minimize deterioration due to arcing.

* Mercury switches - found in thermostats, silent wall switches, and a variety
  of other places, use a small quantity of mercury (a metal which is a liquid
  at room temperature) to complete the circuit.  Depending on the orientation
  of a glass or metal/insulator capsule, the mercury either contacts a set
  of terminals (on) or is separate from them (off).  Since any arcing occurs
  in the liquid mercury, there is virtually no deterioration of internal parts
  of a mercury switch.  Life is nearly infinite when used within its ratings.
  See the section: "About mercury wall switches".

Common problems with switches include: dirt, worn, or melted contacts, broken
plastic or fiber parts, bad connections to terminals.

Testing: Switches can always be tested with a continuity checker or a
multimeter on a low ohms scale.

WARNING: Mercury is a heavy metal and is poisonous.  I know it is fun to play
with beads and globs of the stuff (and I have done it) but do not recommend
it.  Dispose of any from broken mercury switches or thermometers safely.  If
you insist on keeping it, use a piece of paper as a scoop and put the mercury
in a bottle with a tightly sealed cap.

Go to [Next] segment
Go to [Previous] segment

Go to [Table 'O Contents]

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