Notes on the Troubleshooting and Repair of Small Household Appliances
and Power Tools
Notes on the Troubleshooting and Repair of Small Household Appliances and
Power Tools
Version 2.87 (21-Dec-10)
Reproduction of this document in whole or in part is permitted
if both of the following conditions are satisfied:
This notice is included in its entirety at the beginning.
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Table of Contents
Author: Samuel M. Goldwasser
For contact info, please see the
Although working on small appliances is generally less risky than dealing
with equipment like microwave ovens, TVs, and computer monitors, those that
plug into the wall can still produce a very lethal electric shock as well
cause a fire from incorrect or careless repairs both during servicing or
It is essential that you read, understand, and follow all safety
guidelines contained in this document and in the document:
Improper repair of battery operated devices can also result in bad
consequences for you, the device, and any equipment attached to it.
We will not be responsible for damage to equipment, your ego, county wide
power outages, spontaneously generated mini (or larger) black holes, planetary
disruptions, or personal injury or worse that may result from the use of this
Introduction
Note: The chapters: "AC Adapters" and "Batteries" have been relocated to the
document: .
If you have ever tried to get a small household appliance or portable power
tool repaired, you understand why all that stuff is likely to be gathering
dust in your attic or basement closet or junk box.
It does not pay!
may be partially by design.
However, to be fair, it may take just as much
time to diagnose and repair a problem with a $20 toaster as a $300 VCR and
time is money for a repair shop.
It is often not even economical to repair
the more expensive equipment let alone a $40 electric heater.
of the estimate alone would probably buy at least one new unit and possibly
many more.
However, if you can do the repair yourself, the equation changes dramatically
as your parts costs will be 1/2 to 1/4 of what a professional will charge
and of course your time is free.
The educational aspects may also be
appealing.
You will learn a lot in the process.
Many problems can be
solved quickly and inexpensively.
Fixing an old vacuum cleaner to keep
in the rec room may just make sense after all.
This document provides maintenance and repair information for a large number
of small household appliances and portable power tools.
The repair of
consumer electronic equipment is dealt with by other documents in the
"Notes on the Troubleshooting and Repair of..." series.
Suggestions for
additions (and, of course, correction) are always welcome.
You will be able to diagnose problems and in most cases, correct them as
Most problems with household appliances are either mechanical (e.g.,
dirt, lack of or gummed up lubrication, deteriorated rubber parts, broken
doohickies) or obvious electrical (e.g., broken or corroded connections,
short circuits, faulty heating elements) in nature.
With minor exceptions,
specific manufacturers and models will not be covered as there are so many
variations that such a treatment would require a huge and very detailed text.
Rather, the most common problems will be addressed and enough basic principles
of operation will be provided to enable you to narrow the problem down and
likely determine a course of action for repair.
In many cases, you will
be able to do what is required for a fraction of the cost that would be
charged by a repair center - or - be able to revive something that would
otherwise have gone into the dumpster - or remained in that closet until
you moved out of your house (or longer)!
Since so many appliances are variations on a theme - heating, blowing,
sucking, rotating, etc. - it is likely that even if your exact device does
not have a section here, a very similar one does.
Furthermore, with your
understanding of the basic principles of operation, you should be able to
identify what is common and utilize info in other sections to complete a
Should you still not be able to find a solution, you will have learned a great
deal and be able to ask appropriate questions and supply relevant information
if you decide to post to sci.electronics.repair (recommended), alt.home.repair,
or misc.consumers.house.
It will also be easier to do further research using
a repair textbook.
In any case, you will have the satisfaction of knowing you
did as much as you could before finally giving up or (if it is worthwhile
cost-wise) taking it in for professional repair.
With your newly gathered
knowledge, you will have the upper hand and will not easily be snowed by a
dishonest or incompetent technician.
You may not realize the following:
Virtually any table lamp can be restored to a like-new condition
electrically for less than $5 in parts.
The cause of a vacuum cleaner that starts blowing instead of sucking
is likely a dirt clog somewhere.
It is virtually impossible for the
motor to spin in the wrong direction and even if it did, the vacuum
would still have some suction due to the type of blower that is commonly
Many diagnoses of burned out motors are incorrect.
Very often motor
problems are actually something else - and minor.
A truly burned out
motor will often have died spectacularly and under adverse conditions.
It will likely be smelly, charred, or may have created lots of sparks,
tripped a circuit breaker or blew a fuse.
A motor that just stopped
working may be due to worn or gummed up (carbon) brushes, dirt, or a fault
elsewhere in the appliance like a bad connection or switch or circuit - or
the AC outlet might be bad.
The most likely cause of a vacuum cleaner
or other similar appliance that just stopped working is a break in a wire
of the power cord - probably at the plug - due to continual stress from
being dragged around by its tail!
Fluorescent lamps use only 1/3 to 1/2 of the power of an incandescent lamp
of similar light output.
With all the lighting used in an average household,
this can add up particularly for high power ceiling fixtures.
fluorescent light color and quality may not be as aesthetically pleasing
and fixtures or lamps may produce Radio Frequency Interference (RFI) causing
problems with TV or radio reception.
Dimmers can usually not be used
unless they are specifically designed for fluorescent fixtures.
fluorescent lamps do indeed save energy but they can break just like any
other light bulb!
The initial inrush current to an incandescent bulb may be 10 times the
operating current.
This is hard on switches and dimmers and is part of
the reason behind why bulbs tend to burn out when switched on and not
while just sitting there providing illumination.
Furthermore, an erratic
switch or loose connection can shorten the life of an incandescent bulb
due to repeated thermal shock.
And, these are not due to short circuits
but bad intermittent connections.
True short circuits are less common
and should result in a blown fuse or tripped circuit breaker.
Bulb Savers and other devices claiming to extend the life of incandescent
light bulbs may work but do so mostly by reducing power to the bulb at the
expense of some decrease in light output and reduced efficiency.
estimated that soft start alone (without the usual associated reduction in
power) does not prolong the life of a typical bulb by more than a few hours.
Thus, in the end, these device increase costs if you need to use more or
larger bulbs to make up for the reduced light output.
The major life cycle
expense for incandescent lighting is not the cost of the bulbs but the cost
of the electricity - by a factor of 25 to 50!
For example, it costs about
$10 in electricity to run a 100 W bulb costing 25 cents over the course of
its 1000 hour life.
However, these devices (or the use of 130 V bulbs) may
make sense for use in hard-to-reach locations.
Better yet, consider compact
or normal fluorescent bulbs or fixtures which last much longer and are much
more efficient than incandescents (including halogen).
Smart bulbs are legitimate technology with built in automatic off, dimmers,
blink capability, and other 'wizzy' features but they burn out and break just
like ordinary bulbs.
Thus, it hardly makes sense to spend $5 to $10 for
something that will last 1000 to 1500 hours.
Install a proper dimmer,
automatic switch, or external blinker instead.
A Ground Fault Circuit Interrupter (GFCI) protects people against shock
but does not necessarily protect appliances from damage due to electrical
This is the function of fuses, circuit breakers, and thermal
protectors. A GFCI *can* generally be installed in place of a 2-wire
ungrounded outlet to protect it and any outlets downstream.
Check your
local electrical Code to be sure if this is permitted.
Don't waste your money on products like the 'Green Plug', magnetic water
softeners, whole house TV antennas that plug into the wall socket, and
other items of the "it sounds too good to be true' variety.
These are very
effective only at transferring money out of your wallet but rarely work as
advertised.
The Green Plug will not achieve anywhere near the claimed savings and may
actually damage or destroy certain types of appliances like, guess what?:
refrigerators and other induction motor loads.
Ever seen the demo?
The Green Plug is supposed to reduce reactive power (V and I out of phase
due to inductive or capacitive loads) but residential users don't pay for
reactive power anyway, only the real power they use.
In addition, this is
a minor concern for modern appliances.
The demo you see in the store that shows a utility meter slowing down
substantially when the Green Plug is put in the circuit is bogus for two
reasons: (1) The motor being powered is totally unloaded resulting in a
high ratio of reactive to real power.
Under normal use with a motor
driving a load, the reduction in electricity use would be negligible.
(2) The meter is wired to include reactive power in its measurement which,
as noted above, is not the case with residential customers.
Magnetic and radio frequency water softeners are almost certainly 100%
They cloak absolutely useless technology in so much 'technobabble'
that even Ph.D. scientists and engineers have trouble sorting it all out.
The latest wrinkle adds advanced microprocessor control optimized for
each potential mineral deposit.
Yeh, sure.
Mention the word 'magnetism' and somehow, people will pay $300 for $2
worth of magnets that do nothing - and then be utterly convinced of their
effectiveness.
They forget that perhaps the instruction manual suggested
changes in their water use habits - which was the true reason for any
improvement.
Perhaps the magnets can be used to stick papers on the
refrigerator once you discover they don't do anything for the water.
BTW, the same goes for magnetic wine flavor enhancers. :-)
Whole house TV antennas are great for picking up signals with ghosts,
noise, and other distorting effects.
The premise that 'more is better'
is fundamentally flawed when it comes to TV reception.
In rare cases
they may produce a marginally viewable picture in an otherwise unfavorable
location but these are the exceptions.
A pair of set-top rabbit ears will
generally be superior.
I will be happy to revise these comments if someone can provide the results
of evaluations of any of these devices conducted by a recognized independent
testing laboratory.
However, I won't hold my breath waiting.
Basic Appliance Theory
There isn't much rocket science in the typical small appliance (though that
is changing to some extent with the use of microcomputer and fuzzy logic
Everything represents variations on a relatively small number
of basic themes:
Heating - a resistance element similar to what you can see inside a
toaster provides heat to air, liquids, or solids by convections,
conduction, or direct radiant (IR) heat.
Rotation, blowing, sucking - a motor provides power to move air as in
a fan or vacuum cleaner, water as in a sump pump, or provide drive as
in an electric pencil sharpener, food mixer, or floor polisher.
Control - switches and selectors, thermostats and speed regulators,
and microcomputers determine what happens, when, how much, and assure
safe operation.
Relax! This is not going to be a tutorial on computer design.
Appliances
are simple devices.
It is possible to repair many appliance faults without
any knowledge beyond 'a broken wire is probably a problem' or 'this part
is probably bad because it is charred and broken in half'.
However, a
very basic understanding of electrical principles will enable you to more
fully understand what you are doing.
Don't worry, there will be no heavy
The most complicated equations will be variations on Ohm's law:
V=I*R and P=V*V/R.
If you have any sort of background in electricity or electronics, then
you can probably skip the following introductory description - or have
some laughs at my expense.
The easiest way to explain basic electrical theory without serious math
is with a hydraulic analogy.
This is of the plumbing system in your house:
Water is supplied by a pipe in the street from the municipal water company
or by a ground water pump.
The water has a certain pressure trying to
push it through your pipes.
With electric circuits, voltage is the analog
to pressure.
Current is analogous to flow rate.
Resistance is analogous
the difficulty in overcoming narrow or obstructed pipes or partially open
Intuitively, then, the higher the voltage (pressure), the higher the
current (flow rate).
Increase the resistance (partially close a valve or
use a narrower pipe) and for a fixed voltage (constant pressure), the
current (flow rate) will decrease.
With electricity, this relationship is what is known as linear: double the
voltage and all other factors remaining unchanged, the current will double
Increase it by a factor of 3 and the current will triple.
the resistance and for a constant voltage source, the current will double.
(For you who are hydraulic engineers, this is not quite true with plumbing
as turbulent flow sets in, but this is just an analogy, so bear with me.)
Note: for the following 4 items whether the source is Direct Current (DC)
such as a battery or Alternating Current (AC) from a wall outlet does not
The differences between DC and AC will be explained later.
The simplest electrical circuit will consist of several electrical
components in series - the current must flow through all of them to flow
through any of them.
Think of a string of Christmas lights - if one burns
out, they all go out because the electricity cannot pass through the broken
filament in the burned out bulb.
Note the term 'circuit'.
A circuit is a complete loop.
In order for
electricity to flow, a complete circuit is needed.
Switch (3)
_____________/ ______________
+-------+--------+
+---+----+
Power Source
+-------+--------+
+---+----+
Wiring (2)
|_____________________________|
Power source - a battery, generator, or wall outlet.
The hydraulic
equivalent is a pump or dam (which is like a storage battery).
water supply pipe in the street is actually only 'wiring' (analogous
to the electric company's distribution system) from the water company's
reservoir and pumps.
Conductors - the wiring.
Similar to pipes and aqueducts.
Electricity
flows easily in good conductors like copper and aluminum.
These are like
the insides of pipes.
To prevent electricity from escaping, an insulator
like plastic or rubber is used to cover the wires.
Air is a pretty
good insulator and is used with high power wiring such as the power
company's high voltage lines but plastic and rubber are much more
convenient as they allow wires to be bundled closely together.
Switch - turns current on or off.
These are similar to valves which
do not have intermediate positions, just on and off.
A switch is not
actually required in a basic circuit but will almost always be present.
Load - a light bulb, resistance heater, motor, solenoid, etc.
true hydraulic systems such as used to control the flight surfaces of
an aircraft, there are hydraulic motors and actuators, for example.
With household water we usually don't think of the load.
However, things
like lawn sprinklers, dishwasher rotating arms, pool sweepers, and the like
do convert water flow to mechanical work in the home (some homes, at least!).
Hydraulic motors are used to aircraft and spacecraft, large industrial
robots, and all sorts of other applications.
Here are 3 of the simplest appliances:
Flashlight: battery (1), case and wiring (2), switch (3), light bulb (4).
Table lamp: wall outlet (1), line cord and internal wiring (2), power
switch (3), light bulb (4).
Electric fan, vacuum cleaner, garbage disposer: wall outlet (1), line
cord and internal wiring (2), power switch (3), motor (4).
Now we can add one type of simple control device:
Thermostat - a switch that is sensitive to temperature.
This is like an
automatic water valve which shuts off if a set temperature is exceeded.
Most thermostats are designed to open the circuit when a fixed or variable
temperature is exceeded.
However, air conditioners, refrigerators, and
freezers do the opposite - the thermostat switches on when the temperature
goes too high.
Some are there only to protect against a failure elsewhere
due to a bad part or improper use that would allow the temperature to
go too high and start a fire.
Others are adjustable by the user and
provide the ability to control the temperature of the appliance.
With the addition of a thermostat, many more appliances can be constructed
including (this is a small subset):
Electric space heater (radiant), broiler, waffle iron: wall outlet (1),
line cord and internal wiring (2), power switch (3) and/or thermostat (5),
load (heavy duty heating element).
Electric heater (convection), hair dryer: wall outlet (1), line cord
and internal wiring (2), power switch (3) and/or thermostat (5), loads (4)
(heating element and motor).
Electric heaters and cooking appliances usually have adjustable thermostats.
Hair dryers may simply have several settings which adjust heater power and
fan speed (we will get into how later).
The thermostat may be fixed and
to protect against excessive temperatures only.
That's it!
You now understand the basic operating principle of nearly all
small appliances.
Most are simply variations (though some may be quite
complex) on these basic themes.
Everything else is just details.
For example, a blender with 38 speeds just has a set of buttons (switches)
to select various combinations of motor windings and other parts to give
you complete control (as if you need 38 speeds!).
Toasters have a timer
or thermostat activate a solenoid (electromagnet) to pop your bread at
(hopefully) the right time.
Resistances - both unavoidable and functional.
Except for superconductors,
all materials have resistance.
Metals like copper, aluminum, silver, and
gold have low resistance - they are good conductors.
Many other metals
like iron or steel are fair but not quite as good as these four.
NiChrome - an alloy of nickel and chromium - is used for heating elements
because it does not deteriorate (oxidize) in air even at relatively high
temperatures.
A significant amount of the power the electric company produces is lost
to heating of the transmission lines due to resistance and heating.
However, in an electric heater, this is put to good use.
In a flashlight
or table lamp, the resistance inside the light bulb gets so hot that it
provides a useful amount of light.
A bad connection or overloaded extension cord, on the other hand, may
become excessively hot and start a fire.
The following is more advanced - save for later if you like.
Capacitors - energy storage devices.
These are like water storage tanks
(and similar is some ways to rechargeable batteries).
Or, a system
consisting of a a rubber diaphragm separating the water from a volume of
trapped air.
As water is pumped in, energy is stored as the air is
compressed as in the captive air or expansion tanks found in home heating
systems or well water storage tanks.
Capacitors are not that common in small appliances but may be used with
some types of motors and in RFI - Radio Frequency Interference - filters
as capacitors can buffer - bypass - interference to ground.
The energy
to power an electronic flash unit is stored in a capacitor, for example.
Because they act like reservoirs - buffers - capacitors are found in the
power supplies of most electronic equipment to smooth out the various
DC voltages required for each device.
Inductors - their actual behavior is like the mass of water as it flows.
Turn off a water faucet suddenly and you are likely to hear the pipes
banging or vibrating.
This is due to the inertia of the water - it tends
to want to keep moving.
Electricity doesn't have inertia but when wires
are wound into tight coils, the magnetic field generated by electric
current is concentrated and tends to result in a similar effect.
tends to want to continue to flow where inductance is present.
more technical reader, the air chamber used to prevent/minimize the water
hammer effect is the equivalent of an RC snubber!)
The windings of motors and transformers have significant inductance but
the use of additional inductance devices is rare in home appliances
except for RFI - since inductance tends to prevent current from changing,
it can also be used to prevent interference from getting in or out.
Controls - rheostats and potentiometers allow variable control of current
or voltage.
A water faucet is like a variable resistor which can be
varied from near 0 ohms (when on fully) to infinite ohms (when off).
The relationships that govern the flow of current in basic circuits (without
capacitance or inductance - which is the case with many appliances) are
contained in a very simple set of equations known an Ohm's Law.
The simplest of these are:
V = I * R (1)
I = V / R (2)
R = V / I (3)
V is Voltage in Volts (or millivolts - mV or kilovolts - kV).
I is current in amperes (A) or milliamps (mA)
R is resistance in Ohms (ohms), kilo-Ohms (K Ohms), or mega-Ohms (M Ohms).
Power in watts (W) is equal to voltage times current in a resistive circuit
(no capacitance or inductance).
Therefore, rearranging the equations above,
we also obtain:
P = V * V / R
P = I * I * R
For example:
For a flashlight with a pair of Alkaline batteries (3 V) and a light bulb
with a resistance of 10 ohms, we can use (2) to find that the current
is I = (3 V) / (10 ohms) = .3 A.
The from (4) we find that the power
is: P = (3 V * .3 A) = .9 W.
For a blow-dryer rated at 1000 W, the current drawn from a 120 V line
would be: I = P / V (by rearranging (4) = 1000 W / 120 V = 8.33 A.
As noted above:
Increase voltage -> higher current.
(If the water company increases the
pressure, your shower used more water in a given time.)
Decrease resistance -> higher current.
(You have a new wider pipe
installed between the street and your house.
Or, you open the shower
valve wider.)
(Note that the common use of the term 'water pressure' is actually not
The most likely cause of what is normally described as low
water pressure is actually high resistance in the piping between your
residence and the street.
There is a pressure drop in this piping just
as there would be a voltage drop across a high value resistor.)
While electricity can vary in any way imaginable, the most common forms
for providing power are direct current and alternating current:
A direct current source is at a constant voltage.
Displaying the voltage
versus time plot for such a source would show a flat line at a constant
Some examples:
Alkaline AA battery - 1.5 V (when new).
Automotive battery - 12 V (fully charged).
Camcorder battery - 7.2 V (charged).
Discman AC adapter - 9 VDC (fully loaded).
Electric knife AC adapter - 3.6 VDC.
An Alternating Current (AC) source provides a voltage that is varying
periodically usually at 60 Hz (U.S.) or 50 Hz (many other countries).
Note that 1 Hz = 1 cycle per second.
Therefore, a 60 Hz AC voltage
goes through 60 complete cycles in each second.
For power, the shape
of the voltage is a sinusoid which is the smoothest way that anything
can vary periodically between two levels.
The nominal voltage from an AC outlet in the U.S. is around 115 VAC.
is the RMS (Root Mean Square) value, not the peak (0 to maximum).
terms, the RMS value of an AC voltage and the same value of a DC voltage
will result in identical heating (power) to a resistive load.
For example,
115 VAC RMS will result in the same heat output of a broiler as 115 VDC.
Direct current is used for many small motor driven appliances particularly
when battery power is an option since changing DC into AC requires some
additional circuitry.
All electronic equipment require various DC voltages
for their operation.
Even when plugged into an AC outlet, the first thing
that is done internally (or in the AC adapter in many cases) is to convert
the AC to various DC voltages.
The beauty of AC is that a very simple device - a transformer - can
convert one voltage into another.
This is essential to long distance
power distribution where a high voltage and low current is desirable to
minimize power loss (since it depends on the current).
You can see
transformers atop the power poles in your neighborhood reducing the
2,000 VAC or so from a local distribution transformer to your 115 VAC
(actually, 115-0-115 were the total will be used by large appliances like
electric ranges and clothes dryers).
That 2,000 VAC was stepped down
by a larger transformer from around 12,000 VAC provided by the local
substation.
This, in turn, was stepped down from the 230,000 VAC or
more used for long distance electricity transmission.
Some long distance
lines are over 1,000,000 volts (MV).
When converting between one voltage and another with a transformer, the
amount of current (amps) changes in the inverse ratio.
So, using 230 kV
for long distance power transmission results in far fewer heating losses
as the current flow is reduced by a factor of 2,000 over what it would
be if the voltage was only 115 V, for example.
Recall that power loss
from P=I*I*R is proportional to the square of the current and thus in
this example is reduced by a factor of 4,000,000!
Many small appliances include power transformers to reduce the 115 VAC
to various lower voltages used by motors or or electrical components.
Common AC adapters - often simply called transformers or wall warts -
include a small transformer as well.
Where their output is AC, this
is the only internal component other than a fuse or thermal fuse for
protection.
Where their output is DC, additional components convert
the low voltage AC from the transformer to DC and a capacitor smoothes
Up until now, we have been dealing with the series circuit - all parts
are in a single line from power source, wiring, switches, load, and
anything else.
In a series circuit, the current must be the same
through all components.
The light bulb and switch in a flashlight
pass exactly the same value of amperes.
If there were two light bulbs
instead of one and they were connected in series - as in a Christmas
tree light set - then the current must be equal in all the bulbs but
the voltages across each one would be reduced.
The loads, say resistance heating elements, are now drawn with the
schematic symbol (as best as can be done using ASCII) for a resistor.
_____________/ __________________
+-------+--------+
Power Source
+-------+--------+
|_________________________________|
The total resistance, R(T), of the resistors in this series circuit is:
R(T) = R1 + R2
The voltage across each of the resistors would be given by:
V1 = V(S) * R1 / (R1 + R2)
V2 = V(S) * R2 / (R1 + R2)
The current is given by:
/ (R1 + R2)
However, another basic configuration, is also possible.
With a parallel
circuit, components are connected not one after the other but next to
one another as shown below:
_____________/ ___________________________
+-------+--------+
Power Source
+-------+--------+
|_____________________________|____________|
Now, the voltages across each of the loads is necessarily equal but the
individual currents divide according to the relative resistances of each
The total resistance, R(T), of the parallel resistors in this circuit is:
R(T) = (R1 * R2) / (R1 + R2)
The currents through each of the loads would be given by:
I1 = V(S)/R1
I2 = V(S)/R2
The total current is given by:
I = I1 + I2
Many variations on these basic arrangements are possible but nearly all can
be reduced systematically to a combination of series or parallel circuits.
site has some really nice introductory material (with graphics) on a variety
of topics relating to technology in the modern world.
Of relevance to this
document are articles on motors, power adapters, relays, batteries, etc.
in the "Education and Tutorials" area for links to introductory material on
electronics and other related fields.
Appliance Troubleshooting
Appliances run on either AC line power or batteries.
In the latter case,
there is little danger to you except possibly from burns due to short circuits
and heating effect or irritation from the caustic chemicals from old leaky
batteries.
However, AC line power can be lethal.
Proper safety procedures must be
followed whenever working on live equipment (as well as devices which may
have high energy storage capacitors like TVs, monitors, and microwave
AC line power due to its potentially very high current is actually
considerably more dangerous than the 30 kV found in a large screen
These guidelines are to protect you from potentially deadly electrical shock
hazards as well as the equipment from accidental damage.
Note that the danger to you is not only in your body providing a conducting
path, particularly through your heart.
Any involuntary muscle contractions
caused by a shock, while perhaps harmless in themselves, may cause collateral
damage - there are many sharp edges inside this type of equipment as well as
other electrically live parts you may contact accidentally.
For nearly all the appliances we will be covering, there is absolutely
no danger of electrical shock once the unit is unplugged from the wall
socket (not, however, just turned off - the plug should be removed from
the wall socket).
You may have heard warnings about dangers from unplugged appliances.
Perhaps, these were passed down from your great great grandparents or
from local bar room conversation.
Except for devices with large high voltage capacitors connected to the
line or elsewhere, there is nothing inside an appliance to store a
painful or dangerous charge.
Even these situations are only present
in microwave ovens, fluorescent lamps and fixtures with electronic
ballasts, universal power packs for camcorders or portable computers,
or appliances with large motors.
Other than these, once an appliance
is unplugged all parts are safe to touch - electrically that is.
may still be elements or metal brackets that are burning hot as metal
will tend to retain heat for quite a while in appliances like toasters
or waffle irons.
Just give them time to cool.
There are often many
sharp edges on sheetmetal as well.
Take your time and look before you
leap or grab anything.
Note that this list of dangerous appliances doesn't include
CRT-type TVs, computer monitors, and other similar electronic equipment -
which most certainly can store a dangerous charge on the CRT long after
being unplugged - only because they aren't normally considered appliances. :)
The purpose of this set of guidelines is not to frighten you but rather to
make you aware of the appropriate precautions.
Appliance repair can be
both rewarding and economical.
Just be sure that it is also safe!
Don't work alone - in the event of an emergency another person's presence
may be essential.
Always keep one hand in your pocket when anywhere around a powered
line-connected or high voltage system.
Wear rubber bottom shoes or sneakers.
Wear eye protection - large plastic lensed eyeglasses or safety goggles.
Don't wear any jewelry or other articles that could accidentally contact
circuitry and conduct current, or get caught in moving parts.
Set up your work area away from possible grounds that you may accidentally
Know your equipment: small appliances with 2 prong plugs do not use any
part of the outside case for carrying current.
Any metal parts of the
case will either be totally isolated or possibly connected to one side
of the line through a very high value resistor and/or very low value
capacitor.
However, there may be exceptions.
And, failures may occur.
Appliances with 3 prong plugs will have the case and any exposed metal
parts connected to the safety ground.
If circuit boards or other subassemblies need to be removed from their
mountings, put insulating material between them and anything they may
Hold them in place with string or electrical tape.
up with insulation sticks - plastic or wood.
Parts of heating appliances can get very hot very quickly.
carefully test before grabbing hold of something you will be sorry about
If you need to probe, solder, or otherwise touch circuits with power off,
discharge (across) large power supply filter capacitors with a 2 W or greater
resistor of 100-500 ohms/V approximate value (e.g., for a 200 V capacitor
use a 50 K ohm resistor).
The only places you are likely to find large
capacitors in small appliance repair are in induction motor starting or
running circuitry or the electronic ballasts of fluorescent fixtures.
Connect/disconnect any test leads with the equipment unpowered and
unplugged. Use clip leads or solder temporary wires to reach cramped
locations or difficult to access locations.
Perform as many tests as possible with the device unplugged.
the power switch supposedly off, if the unit is plugged into a live outlet,
line voltage may be present in unexpected places or probing may activate
a motor due to accidentally pressing a microswitch.
Most parts in
household appliances and power tools can be can be tested using only
an ohmmeter or continuity checker.
If you must probe live, put electrical tape over all but the last 1/16"
of the test probes to avoid the possibility of an accidental short which
could cause damage to various components.
Clip the reference end of the
meter or scope to the appropriate ground return so that you need to only
probe with one hand.
Use an isolation transformer if there is any chance of contacting line
connected circuits.
A Variac(tm) is not an isolation transformer!
The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a
good idea but will not protect you from shock from many points in a line
connected TV or monitor, or the high voltage side of a microwave oven, for
(Note however, that, a GFCI may nuisance trip at power-on or at
other random times due to leakage paths (like your scope probe ground) or
the highly capacitive or inductive input characteristics of line powered
equipment.)
A fuse or circuit breaker is too slow and insensitive to provide
any protection for you or in many cases, your equipment.
However, these
devices may save your scope probe ground wire should you accidentally connect
it to a live chassis.
Don't attempt repair work when you are tired.
Not only will you be more
careless, but your primary diagnostic tool - deductive reasoning - will
not be operating at full capacity.
Finally, never assume anything without checking it out for yourself!
Don't take shortcuts!
There is no hard and fast rule.
Personally, I do unplug heating appliances
when I am done with them.
The quality of internal construction is not always
that great and this is a minor annoyance to avoid a possible fire hazard
should something fail or should such an appliance accidentally be left on.
BTW, electronic equipment should always be unplugged during lightning
storms since it may be very susceptible to power surge and lightning
Don't forget the telephones and computer modems as well.
This is not as much of a problem with small appliances that do not
include electronic controllers as except for direct lightning strikes,
the power switch will provide protection.
Many problems have simple solutions.
Don't immediately assume that
your problem is some combination of esoteric complex convoluted
For a dead appliance, the most likely cause might just be
a bad line cord or plug!
Try to remember that the problems with the most
catastrophic impact on operation (an appliance that blows fuses) usually
have the simplest causes (a wire shorting due to frayed insulation).
If you get stuck, sleep on it.
Sometimes, just letting the problem
bounce around in your head will lead to a different more successful
approach or solution.
Don't work when you are really tired - it is both
dangerous and mostly non-productive (or possibly destructive - especially
with AC line powered appliances).
Whenever working on precision equipment, make copious notes and diagrams.
Yes, I know, a toaster may not exactly be precision equipment, but trust me.
You will be eternally grateful when the time comes to reassemble the unit.
Most connectors are keyed against incorrect insertion or interchange
of cables, but not always.
Apparently identical screws may be of differing
lengths or have slightly different thread types.
Little parts may fit in
more than one place or orientation.
Pill bottles, film canisters, and plastic ice cube trays come in handy for
sorting and storing screws and other small parts after disassembly.
Select a work area which is well lighted and where dropped parts can
be located - not on a deep pile shag rug.
Something like a large plastic
tray with a slight lip may come in handy as it prevents small parts from
rolling off of the work table.
The best location will also be relatively
dust free and allow you to suspend your troubleshooting to eat or sleep or
think without having to pile everything into a cardboard box to eat dinner.
A basic set of precision hand tools will be all you need to work on
most appliances.
These do not need to be really expensive but poor quality
tools are worse than useless and can cause damage.
Stanley and Craftsman
tools are fine.
Needed tools include a selection of Philips and straight
blade screwdrivers, socket drivers, open end or adjustable wrenches of various
sizes, needlenose pliers, wire cutters, tweezers, and dental picks.
An electric drill or drill press with a set of small (1/16" to 1/4") high
quality high speed drill bits is handy for some types of restoration where
new holes need to be provided.
A set of machine screw taps is also useful
A medium power soldering iron and rosin core solder (never never use
acid core solder or the stuff for sweating copper pipes on electrical
or electronic repairs!) will be required if you need to make or replace any
soldered connections.
A soldering gun is desirable for any really beefy
soldering.
See the section: .
A crimping tool and an assortment of solderless connectors often called
'lugs' will be needed to replace damaged or melted terminals in small
appliances.
See the section: .
Old dead appliances can often be valuable sources of hardware and sometimes
even components like switches and heating elements.
While not advocating
being a pack rat, this does have its advantages at times.
Soldering is a skill that is handy to know for many types of construction
and repair.
For modern small appliances, it is less important than it once
was as solderless connectors have virtually replaced solder for internal
However, there are times where soldering is more convenient - for
example, when performing repairs at 1 AM and a replacement crimp lug is not
available.
Use of the proper technique is critical to reliability and safety.
solder connection is not just a bunch of wires and terminals with solder
dribbled over them.
When done correctly, the solder actually bonds to the
surface of the metal (usually copper) parts.
CAUTION: You can easily turn a simple repair (e.g., bad solder connections)
into an expensive mess if you use inappropriate soldering equipment and/or
lack the soldering skills to go along with it.
If in doubt, find someone else
to do the soldering or at least practice, practice, practice, soldering and
desoldering on a junk unit first!
Effective soldering is by no means difficult but some practice may be needed
to perfect your technique.
The following guidelines will assure reliable solder joints:
Only use rosin core solder (e.g., 60/40 tin/lead) for electronics work.
A 1 pound spool will last a long time and costs about $10.
diameter is .030 to .060 inches for appliances.
The smaller size is
preferred as it will be useful for other types of precision electronics
repairs or construction as well.
The rosin is used as a flux to clean
the metal surface to assure a secure bond.
NEVER use acid core solder
or the stuff used to sweat copper pipes!
The flux is corrosive and
it is not possible to adequately clean up the connections afterward to
remove all residue.
Keep the tip of the soldering iron or gun clean and tinned.
Buy tips that
are permanently tinned - they are coated and will outlast countless normal
copper tips.
A quick wipe on a wet sponge when hot and a bit of solder
and they will be as good as new for a long time.
(These should never be
filed or sanded).
Make sure every part to be soldered - terminal, wire, component leads -
is free of any surface film, insulation,
or oxidation.
Fine sandpaper or
an Xacto knife may be used, for example, to clean the surfaces.
The secret
to a good solder joint is to make sure everything is perfectly clean
and shiny and not depend on the flux alone to accomplish this. Just make
sure the scrapings are cleared away so they don't cause short circuits.
Start with a strong mechanical joint.
Don't depend on the solder to
hold the connection together.
If possible, loop each wire or component
lead through the hole in the terminal.
If there is no hole, wrap them
once around the terminal.
Gently anchor them with a pair of needlenose
Use a properly sized soldering iron or gun: 20-25 W iron for fine circuit
25-50 W iron for general soldering of terminals and wires
100-200 W soldering gun for chassis and large
area circuit planes.
With a properly sized iron or gun, the task will be
fast - 1 to 2 seconds for a typical connection - and will result in little
or no damage to the circuit board, plastic switch housings, insulation,
Large soldering jobs will take longer but no more than 5 to 10
seconds for a large expanse of copper.
If it is taking too long, your
iron is undersized for the task, is dirty, or has not reached operating
temperature.
For appliance work there is no need for a fancy soldering
station - a less than $10 soldering iron or $25 soldering gun as
appropriate will be all that is required.
Heat the parts to be soldered, not the solder.
Touch the end of the solder
to the parts, not the soldering iron or gun.
Once the terminal, wires,
or component leads are hot, the solder will flow via capillary action, fill
all voids, and make a secure mechanical and electrical bond.
Sometimes,
applying a little from each side will more effectively reach all nooks
and crannies.
Don't overdo it.
Only enough solder is needed to fill all voids.
resulting surface should be concave between the wires and terminal, not
bulging with excess solder.
Keep everything absolutely still for the few seconds it takes the solder
to solidify.
Otherwise, you will end up with a bad connection - what is
called a 'cold solder joint'.
A good solder connection will be quite shiny - not dull gray or granular.
If your result is less than perfect reheat it and add a bit of new solder
with flux to help it reflow.
Practice on some scrap wire and electronic parts.
It should take you about
3 minutes to master the technique!
Occasionally, it will be necessary to remove solder - either excess or
to replace wires or components.
A variety of tools are available for
this purpose.
The one I recommend is a vacuum solder pump called
'SoldaPullet' (about $20).
Cock the pump, heat the joint to be cleared,
and press the trigger.
Molten solder is sucked up into the barrel of the
device leaving the terminal nearly free of solder.
Then use a pair of
needlenose pliers and a dental pick to gently free the wires or component.
Other approaches that may be used in place of or in addition to this:
Solder Wick which is a copper braid that absorbs solder via capillary
rubber bulb type solder pumps, and motor driven vacuum solder
rework stations (pricey).
See the document:
for additional info on desoldering of
electronic components.
The thermoplastic used to mold many common cheap connectors softens or
melts at relatively low temperatures.
This can result in the pins popping
out or shifting position (even shorting) as you attempt to solder to them
to replace a bad connection, for example.
One approach that works in some cases is to use the mating socket to stabilize
the pins so they remain in position as you solder.
The plastic will still
melt - not as much if you use an adequately sized iron since the socket will
act as a heat sink - but will not move.
An important consideration is using the proper soldering iron.
cases, a larger iron is better - you get in and out more quickly without
heating up everything in the neighborhood.
Most internal connections in small appliances are made using solderless
connectors.
These include twist on WireNuts(tm) and crimped terminal lugs
of various sizes and configurations.
WireNuts allow multiple wires to be joined by stripping the ends and then
'screwing' an insulated thimble shaped plastic nut onto the grouped ends
of the wires.
A coiled spring (usually) inside tightly grips the bare
wires and results in a mechanically and electrically secure joint.
appliance repair, the required WireNuts will almost always already be
present since they can usually be reused.
If you need to purchase any,
they come in various sizes depending on the number and size of the wires
that can be handled.
It is best to twist the individual conductor strands
of each wire together and then twist the wires together slightly before
applying the WireNut.
Crimped connectors, called lugs, are very common in small appliances.
reason is that it is easier, faster, and more reliable, to make connections
using these lugs with the proper crimping equipment than with solder.
A lug consists of a metal sleeve which gets crimped over one or more wires,
an insulating sleeve (usually, not all lugs have these), and a terminal
connection: ring, spade, or push-on are typical.
Lugs connect one or more wires to the fixed terminals found on switches,
motors, thermostats, and so forth.
There are several varieties:
Ring lugs - the end looks like an 'O' and must be installed on a threaded
terminal of similar size to the opening in the ring.
The screw or nut must
be removed to replace a ring lug.
Spade lugs - the end looks like a 'U' and must be installed on a threaded
terminal of similar size to the opening in the spade.
These can be slipped
on and off without entirely removing the screw or nut.
Push-on lugs - called 'FastOns' by one manufacturer.
The push-on terminal
makes a tight fit with a (usually) fixed 'flag'.
There may also be a latch
involved but usually just a pressure fit keeps the connection secure.
However, excessive heat over time may weaken these types of connections,
resulting in increased resistance, additional heating, and a bad connection
or melt-down.
The push-on variety are most common in small appliances.
In the factory, the lugs are installed on the wires with fancy expensive
equipment.
For replacements, an inexpensive crimping tool and an assortment
of lugs will suffice.
The crimping tool looks like a pair of long pliers
and usually combines a wire stripper and bolt cutter with the crimping
It should cost about $6-10.
The crimping tool 'squashes' the metal sleeve around the stripped ends of the
wires to be joined.
A proper crimp will not come apart if an attempt is made
to pull the wires free - the wires will break somewhere else first.
gas-tight - corrosion (within reason) will not affect the connection.
Crimping guidelines:
Use the proper sized lug.
Both the end that accepts the wire(s) and the
end that screws or pushes on must be sized correctly.
Easiest is to
use a replacement that is identical to the original.
Where this is not
possible, match up the wire size and terminal end as closely as possible.
There will be a minimum and maximum total wire cross sectional area that
is acceptable for each size.
Avoid the temptation to trim individual
conductor strands from wires that will not fit - use a larger size lug.
Although not really recommended, the bare wires can be doubled over to
thicken them for use with a lug that is slightly oversize.
For heating appliances, use only high temperature lugs.
This will assure
that the connections do not degrade with repeated temperature cycles.
Strip the wire(s) so that they fit into the lug with just a bit showing
out the other (screw or push-on) end.
Too long and your risk interference
with the terminals and/or shorting to other terminals.
Too short and it
is possible that one or more wires will not be properly positioned, will
not be properly crimped, and may pull out or make a poor connection.
insulation of the wires should be within the insulating sleeve - there
should be no bare wire showing behind the lug.
Crimp securely but don't use so much force that the insulating sleeve
or metal sleeve is severed.
Usually 1 or 2 crimps for the actual wire
connection and 1 crimp to compress the insulating sleeve will be needed.
Test the crimp when complete - there should be no detectable movement of
the wires.
If there is, you didn't crimp hard enough or the lug is
too large for your wires.
In order to make most connections, the plastic or other insulating covering
must be removed to expose the bare copper conductors inside.
way to do this is with a proper wire stripper which is either adjustable
or has dedicated positions for each wire size.
It is extremely important
that the internal conductor (single wire or multiple strands) are undamaged.
Nicks or loss of some strands reduces the mechanical and electrical integrity
of the connection.
In particular, a seriously nicked wire may break off
at a later time - requiring an additional repair or resulting in a safety
hazard or additional damage.
The use of a proper wire stripper will greatly
minimize such potential problems.
A pen knife or Xacto knife can be used in a pinch but a wire stripper is
really much much easier.
Screw terminals are often seen in appliances.
In most cases, lugs are
used to attach one or more wires to each terminal and when properly done,
this usually is the best solution.
However, in most cases, you can attach
the wire(s) directly if a lug is not available:
The best mechanical arrangement is to put the wire under a machine screw
or nut, lock washer, and flat washer.
However, you will often see just
the screw or nut (as in a lamp switch or wall socket).
applications, this is satisfactory.
Avoid the temptation to put multiple wires around a single terminal
unless you separate each one with a flat washer.
Strip enough of the wire to allow the bare wire to be wrapped once around
the terminal.
To much and some will poke out and migh
too little and a firm mechanical joint and electrical connection may be
impossible.
For multistranded wire, tightly twist the strands of stripped wire together
in a clockwise direction as viewed from the wire end.
Wrap the stripped end of the wire **clockwise** around the terminal post
(screw or stud) so that it will be fully covered by the screw head, nut,
or flat washer.
This will insure that the wire is grabbed as the screw
or nut is tightened.
A pair of small needlenose pliers may help.
Hold onto the wire to keep it from being sucked in as the screw or nut
is tightened.
Don't overdo it - you don't need to sheer off the head
of the screw to make a secure reliable connection.
Inspect the terminal connection: the bare wire should be fully covered
by the head of the screw, nut, or flat washer.
Gently tug on the wire
to confirm that it is securely fastened.
Very little test equipment is needed for most household appliance repair.
First, start with some analytical thinking.
Many problems associated
with household appliances do not require a schematic.
Since the internal
wiring of many appliances is so simple, you will be able to create your
own by tracing the circuits in any case.
However, for more complex
appliances, a schematic may be useful as wires may run behind and under
other parts and the operation of some custom switches may not obvious.
The causes for the
majority of problems will be self evident once you gain
access to the interior - loose connections or broken wires, bad switches,
open heating element, worn motor brushes, dry bearings.
All you will need
are some basic hand tools, a circuit and continuity tester, light oil and
grease, and your powers of observation (and a little experience).
built in senses and that stuff between your ears represents the most
important test equipment you have.
The following will be highly desirable for all but the most obvious problems:
Circuit tester (neon light) - This is used to test for AC power or confirm
that it is off.
For safety, nothing can beat the simplicity of a neon
Its use is foolproof as there are no mode settings or range
selections to contend with.
Touch its two probes to a circuit and if it
lights, there is power.
(This can also take the place of an Outlet
tester but it is not as convenient (see below).
Cost: $2-$3.
Outlet tester (grounds and miswiring) - This will confirm that a 3 prong
outlet is correctly wired with respect to Hot, Neutral, and Ground.
not 100% assured of correct wiring if the test passes, the screwup would
need to be quite spectacular.
This simple device instantly finds missing
Grounds and interchanged Hot and Neutral - the most common wiring mistakes.
Just plug it into an outlet and if the proper two neon light are lit at
full brightness, the outlet is most likely wired correctly.
Cost: about $6.
These are just a set of 3 neon bulbs+resistors across each pair of wires.
If the correct bulbs light at full brightness - H-N, H-G - then the
circuit is likely wired correctly.
If the H-G light is dim or out or
if both the H-G and G-N are dim, then you have no ground.
If the N-G
light is on and the H-G light is off, you have reversed H and N, etc.
What it won't catch: Reversed N and G (unlikely unless someone really
screwed up) and marginal connections since the neon bulbs doesn't use much
For this (particularly important for the G since it won't do any
good if its resistance back to the service panel is too high) you need a
real load like a 100 W light bulb.
Or, build a tester consisting of 100 W
light bulbs (instead of neon lamps) wired between each of the prongs.
It also won't distinguish between 110 VAC and 220 VAC circuits
except that the neon bulbs will glow much brighter on 220 VAC but without
a direct comparison, this could be missed.
For something that appears to test for everything but next week's weather:
(From: Bill Harnell (bharne@adss.on.ca).)
Get an ECOS 7105 tester! (ECOS Electronics Corporation, Oak Park, Illinois,
708-383-2505).
Not cheap, however.
It sold for $59.95 in 1985 when I
purchased somewhere around 600 of them for use by our Customer Engineers
for safety purposes!
It tests for:
Correct wiring, reversed polarity, open Ground, open Neutral, open Hot,
Hot & Ground reversed, Hot on neutral, Hot unwired, other errors,
over voltage (130 VAC+), under voltage (105 VAC-), Neutral to Ground short,
Neutral to Ground reversal, Ground impedance test (2 Ohms or less ground
impedance - in the equipment ground conductor).
Their less expensive 7106 tester performs almost all of the above tests.
FWIW, I have no interest in the ECOS Corporation of any kind. Am just a
very happy customer.
Continuity tester (buzzer or light) - Since most problems with appliances
boil down to broken connections, open heating elements, defective switches,
shorted wires, and bad motor windings, a continuity tester is all that
is needed for most troubleshooting.
A simple battery operated buzzer or
light bulb quickly identifies problems.
If a connection is complete, the
buzzer will sound or the light will come on.
Note that a dedicated
continuity tester is preferred over a similar mode on a multimeter because
it will operate only at very low resistance.
The buzzer on a multimeter
sounds whenever the resistance is less than about 200 ohms - a virtual open
circuit for much appliance wiring.
A continuity tester can be constructed very easily from an Alkaline
battery, light bulb or buzzer, some wire, and a set of test leads with
All of these parts are available at Radio Shack.
AA, C, or D cell
1.5 V flashlight bulb or buzzer
+------------------+
Test probe 1
o-----------| |--------------|
Bulb or buzzer
+------------------+
Test probe 2
o-------------------------------------------------------+
CAUTION: Do not use this simple continuity tester on electronic equipment
as there is a slight possibility that the current provided by the battery
will be too high and cause damage.
It is fine for most appliances.
GFCI tester - outlets installed in potentially wet or outdoor areas should
be protected by a Ground Fault Circuit Interrupter (GFCI).
A GFCI is now
required by the NEC (Code) in most such areas.
This tester will confirm
that any outlets protected by a GFCI actually will trip the device if there
is a fault.
It is useful for checking the GFCI (though the test button
should do an adequate job of this on its own) as well as identifying or
testing any outlets downstream of the GFCI for protection.
Wire a 3 prong plug with a 15 K ohm 1 W resistor between H and G.
and label it!
This should trip a GFCI protected outlet as soon as it is
plugged in since it will produce a fault current of about 7 mA.
Note that this device will only work if there is an actual Safety Ground
connection to the outlet being tested.
A GFCI retrofitted into a 2 wire
installation without a Ground cannot be tested in this way since a GFCI
does not create a Ground.
However, jumpering this rig between the H and
and a suitable earth ground (e.g., a cold water in an all copper plumbing
system) should trip the GFCI.
Therefore, first use an Outlet Tester
(above) to confirm that there is a Safety Ground present.
The test button works because it passes an additional current through the
sense coil between Hot and Neutral tapped off the wiring at the line side
of the GFCI and therefore doesn't depend on having a Ground.
If you want to be fancier, you can build a combination outlet and GFCI
Wire up a neon indicator with current limiting resistor) across
each pair of wires.
Add a 15K ohm 1 W resistor in series with a pushbutton
switch between H and G.
If the H-G neon is lit (indicating a proper Ground
connection), pressing the button should trip the GFCI.
Multimeter (VOM or DMM) - This is necessary for actually measuring
voltages and resistances.
Almost any type will do - even the $14.95
special from Sears.
Accuracy is not critical for household appliance
repair but reliability is important - for your safety if no other
It doesn't really matter whether it is a Digital MultiMeter (DMM)
or analog Volt Ohm Meter (VOM).
A DMM may be a little more robust should
you accidentally put it on an incorrect scale.
However, they both serve
the same purpose.
A cheap DMM is also not necessarily more accurate than
a VOM just because it has digits instead of a meter needle.
A good quality
well insulated set of test leads and probes is essential.
What comes with
inexpensive multimeters may be too thin or flimsy.
Replacements are
available.
Cost: $15-$50 for a multimeter that is perfectly adequate for
home appliance repair.
Note: For testing of household electrical wiring, a VOM or DMM can indicate
voltage between wires which is actually of no consequence.
This is due to
the very high input resistance/impedance of the instrument.
The voltage
would read zero with any sort of load.
See the section:
Once you get into electronic troubleshooting, an oscilloscope, signal
generator, and other advanced (and expensive) test equipment will be useful.
For basic appliance repair, such equipment would just gather dust.
Yes, you will void the warranty, but you knew this already.
Appliance manufacturers seem to take great pride in being very mysterious
as to how to open their equipment.
Not always, but this is too common
to just be a coincidence.
A variety of techniques are used to secure the covers on consumer
electronic equipment:
Yes, many still use this somewhat antiquated technique.
Sometimes, there are even embossed arrows on the case indicating
which screws need to be removed to get at the guts.
In addition to
obvious screw holes, there may be some that are only accessible when a
battery compartment is opened or a trim panel is popped off.
These are almost always of the Philips variety though more and more
appliances are using Torx or security Torx type screws.
Many of these
are hybrid types - a slotted screwdriver may also work but the Philips
or Torx is a whole lot more convenient.
A precision jeweler's
screwdriver set including miniature Philips
head drivers is a must for repair of miniature portable devices.
Hidden screws:
These will require prying up a plug or peeling off
a decorative decal.
It will be obvious that you were tinkering - it
is virtually impossible to put a decal back in an undetectable way.
Sometimes the rubber feet can be pryed out revealing screw holes.
a stick-on label, rubbing your finger over it may permit you to locate
a hidden screw hole.
Just puncture the label to access the screw as this
may be less messy then attempting to peel it off.
Look around the seam between the two halves.
You may (if
you are lucky) see points at which gently (or forcibly) pressing with a
screwdriver will unlock the covers.
Sometimes, just going around the seam
with a butter knife will pop the cover at one location which will then
reveal the locations of the other snaps.
Or more likely, the plastic is fused together.
particularly common with AC adapters (wall warts).
In this case, I usually
carefully go around the seam with a hacksaw blade taking extreme care not
to go through and damage internal components.
Reassemble with plastic
electrical tape.
It isn't designed for repair.
Don't laugh.
I feel we will see more
and more of this in our disposable society.
Some devices are totally
potted in Epoxy and are 'throwaways'.
With others, the only way to open
them non-destructively is from the inside.
Don't force anything unless you are sure there is no alternative - most
of the time, once you determine the method of fastening, covers will
come apart easily.
If they get hung up, there may be an undetected
screw or snap still in place.
However, sometimes it is just impossible (by
design) to disassemble an appliance without doing some damage.
That's life
(and aids the manufacturer's bottom line!).
When reinstalling the screws, first turn them in a counter-clockwise direction
with very slight pressure. You will feel them "click" as they fall into the
already formed threads.
Gently turn clockwise and see if they turn easily.
If they do not, you haven't hit the previously formed threads - try again.
Then just run them in as you normally would. You can always tell when you
have them into the formed threads because they turn very easily for nearly
the entire depth.
Otherwise, you will create new threads which will quickly
chew up the soft plastic.
Note: these are often high pitch screws - one turn
is more than one thread - and the threads are not all equal.
The most annoying (to be polite) situation is when after removing the
18 screws holding the case together (losing 3 of them entirely and mangling
the heads on 2 others), removing three subassemblies, and two other circuit
boards, you find that the adjustment you wanted was accessible through a
hole in the case just by partially peeling back a rubber hand grip! (It
has happened to me).
When reassembling the equipment make sure to route cables and other wiring
such that they will not get pinched or snagged and possibly broken or have
their insulation nicked or pierced and that they will not get caught in
moving parts.
This is particularly critical for AC line operated appliances
and those with motors to minimize fire and shock hazard and future damage
to the device itself.
Replace any cable ties that were cut or removed during
disassembly and add additional ones of your own if needed.
Some electrical
tape may sometimes come in handy to provide insulation insurance as well.
As long as it does not get in the way, additional layers of tape will not
hurt and can provide some added insurance against future problems.
put a layer of electrical tape around connections joined with WireNuts(tm)
as well just to be sure that they will not come off or that any exposed wire
will not short to anything.
This should be the first step in any inspection and cleaning procedure.
Appliances containing fans or blowers seem to be dust magnets - an incredible
amount of disgusting fluffy stuff can build up in a short time - even with
built-in filters.
Use a soft brush (like a new cheap paint brush) to remove as much dirt,
dust, and crud, as possible without dist}