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


  7.123) How to add an addition button to a door bell

Refer to the diagram in the section: "Electromechanical doorbells and chimes",

Another button can be added in parallel with any of the existing ones (i.e.,
between points X and F or X and B in the diagram).  The only restriction is
that you may not be able to have more than one lighted button in each group
as the current passing through the lighted bulbs may be enough to sound the
chimes - at least weakly.

If you cannot trace the wiring (it is buried inside the wall or ceiling)
the only unknown is which side of the transformer to use.  If you pick the
wrong one, nothing will happen when you press the button.

  7.124) Wireless doorbells or chimes

The transmitter and receiver portion of these units are virtually identical
to those of garage door operators.  See the relevant sections on those units
for problems with activation.

The bell or chimes portion may be either an electromechanical type - a coil
forming an electromagnet which pulls in a plunger to strike a gong or bell.
See the section: "Electromechanical doorbells and chimes".

Others are fully electronic synthesizing an appropriate tone, series of tones,
or even a complete tune on demand.  Repair of the electronics is beyond the
scope of this document.  However, there are several simple things that can
be done:

* Check for dead batteries and dirty battery contacts in both the pushbutton
  and chimes unit.

* Confirm that the channel selection settings have not accidentally been
  changed on the pushbutton or chimes unit.  Flick each switch back and
  forth (where switches are used) just to make sure they are firmly seated.

* Check for improper programming or program loss due to a power failure (if
  AC operated) on units that are more sophisticated than a personal computer.

  7.125) Doorbell rings on its own

* For mechanical chimes, this is almost certainly an intermittent short
  circuit in the button wiring or a defective button.  First check or replace
  the outside pushbutton switches as this is the most likely location due to
  environment and small multilegged creatures.

* For electronics chimes, the problem could either be in the transmitter(s) or
  chimes unit or due to external interference.  Someone in your vicinity could
  have the model also set to the default code (which is probably what you
  have, correct?).

  First, remove the batteries or kill power to all transmitters and wait see if
  the problem still occurs.

  - If it does, either the chimes unit is defective or there is an external
    source of interference.

  - If it now behaves, try each one individually to identify the culprit.
    In some cases, a low battery could produce these symptoms as well.

  7.126) Old garage door operator guts for wireless chime

Don't toss the electronic remains of that old garage door operator.  It would
probably be possible to use it as the basis for a wireless doorbell.  Instead
of starting the motor, use its output to enable an electronic chime or buzzer.
The RF transmitter and receiver for a wireless chime is virtually identical
to that of a typical garage door operator.

  7.127) TV antenna rotators

These consist of a base unit with some sort of direction display and knob
and a motor unit to which the TV antenna is mounted.  Of course, the
troubleshooting of these installations is complicated, of course, by the
remote and somewhat inaccessible location of the motor unit :-(.  Before
climbing up on the third story roof, confirm that you haven't lost power
to the motor unit and/or base station and that the connections between
them are secure.

A common type of motor that may be used in these is a small AC split phase or
capacitor run induction motor.  The relative phase of the main and phase coils
determines the direction.  These probably run on 115 VAC.  A capacitor may
also be required in series with one of the windings.  If the antenna does not
turn, a bad capacitor or open winding on the motor is possible.  See the
chapter: "Motors 101" for more info on repair of these types of motors.

The base unit is linked to the motor unit in such a way that the motor
windings are powered with the appropriate phase relationship to turn the
antenna based on the position of the direction control knob.  This may
be mechanical - just a set of switch contacts - or electronic - IR detectors,
simple optical encoder, etc.

Chapter 8) Power Tools

  8.1) Types of motors found in power tools

A variety of motor types are used depending on the type of tool.  AC powered
portable tools usually use a universal motor due to it high power/weight
ratio and ease of electronic speed control.  Cordless tools usually use a
high performance permanent magnet DC motor.  Stationary power tools almost
always use some form of AC induction motor except where variable speed
is required.  

See the sections on these types of motors for more details than the following
summaries provide.

  8.2) Motors in AC line operated portable tools

Line operated portable (corded) power tools usually use a universal type
AC motor providing 3,000 to 30,000 RPM at the motor shaft.  For the same
power rating, these will be significantly lighter than an induction motor.

A single or multiple stage gear reducer drops the relatively high speed
at which these motors are most efficient to whatever the tool actually
requires, increasing the torque as well.

Universal motors can also be speed controlled relatively easily using a
variant of a simple light dimmer type circuit.  Excellent torque is
maintained over a very wide range extending to nearly 0 RPM.

  8.3) Motors in cordless power tools

These are usually high performance permanent magnet DC motors using advanced
high strength and exotic magnetic materials.  They are very compact and light
weight for their power output.  As with all DC (brush type) motors, brush
wear is a common problem.

Speed control is easily accomplished by low cost electronic circuits which
chop the power (pulse width modulation) rather than simply using a rheostat.
This is much more efficient - extremely important with any battery operated

  8.4) Motors in stationary power tools

Stationary power tools which do not require continuous speed control will
generally use some type of AC induction motor - split phase or capacitor
start/run.  The motors generally operate at a fixed speed of around either
1725 or 3450 RPM (U.S., 60 Hz power).  Stepped pulleys or continuous mechanical
speed/torque changers are used to obtain (usually) lower work piece speeds.

For example, a typical drill press may have one or two sets of stepped
pulleys providing 3 to 15 or more speeds by changing belt positions.  A
continuously variable cone drive is also available as an option on some
models.  This is extremely convenient but does add cost and is usually not
found on less expensive models.

An internal thermal overload protector may be incorporated into larger
motors.  WARNING: this may be self resetting.  If the tool stops on its own,
switch off and unplug it before attempting to determine the cause.

Generally, these induction motors are virtually maintenance-free though
cleaning, tensioning, and lubrication may be required of the drive system.

However, electronic speed control of induction motors, while possible,
is relatively complex and expensive requiring a variable frequency
variable voltage power supply.  Therefore, universal motors may be used
on stationary tools like scroll saws with continuously variable electronic
speed control.

  8.5) About horsepower ratings

One horsepower is equal to 746 watts of electrical power (100% efficiency).
Therefore, the most you can get continuously from a normal 115 V 15 A outlet
is about 2 HP.  Any claims (for air compressors, for example) of higher
ratings on a normal outlet are totally bogus.  Companies such as Sears
(Craftsman) like to specify 'Reserve Power' for their power tools which
as best as I can determine refers to the power available for a short time
and may relate to the mass - and inertia - of the rotating parts but not
the continuous power available.  This may be useful to help saw through
a tough knot in a piece of hardwood but may not be terribly meaningful for
a wet/dry vacuum!  Therefore, pay most attention to the continuous power
ratings if they can be found anywhere.  A good indication is probably the
maximum amps required for the electrical service.

As with over-the-counter drugs, extra strength does not necessarily translate
into faster relief, higher current does not always mean better performance,
and horsepower ratings much above what you would compute from V x A may be
more of a marketing gimmick than anything really beneficial.

  8.6) Cords for AC line operated portable power tools

Really old power tools had two wire cord plugs and no safety ground yet were
of all metal (solid and heavy!) construction.  I would recommend that as
a matter of policy, these be retrofitted with a 3 wire grounded cordset.

Newer ones have the grounded cordset while the newest 'double insulated
tools' are of mostly plastic construction and are back to a 2 wire ungrounded

As with any electrical appliances, inspect cords regularly and repair or
replace any that are seriously damaged - if the inner wiring is showing,
nicked, or cut; if the plug is broken or gets hot during use, or where
the cord is pulled from or broken at the strain relief.

  8.7) Portable drills

The portable electric drill (now the rage is cordless) is probably one of
the two first tools that any handyman should own (the other being a saber
saw).  It is used for many things in addition to drilling little holes -
drilling large holes, sanding, polishing, driving screws, etc.  Therefore,
these tools get a lot of use - and abuse.

  8.8) AC line powered drills

An AC line powered electric drill is just a universal motor with a two stage
(typical) gear reduced powering a chuck to hold the drill bit or attachment.
A continuous range speed control with a reversing switch is now standard
on most AC line powered drills.

Typical problems include:

* Worn bearings.  These may be replaceable.  Also see the section: "Upgrading the bearings on a Craftsman drill".

* Worn motor brushes.  Replacements should be available. from the manufacturer
  or a motor/appliance repair shop.

* Broken or chipped gears.  This is rare under normal conditions but
  if the drill was abused, then failure is possible.

* Bad cord or plug.  Repair or replace for safety reasons.

* Bad speed controller/reversing switch.  Replacement trigger assemblies
  are available but may cost half as much as an entire new drill.  One
  common wear item is the linear potentiometer operated by the trigger
  and this is not likely to be a standard component.  The drill may work
  fine as a single speed model if this control fails.  You could always
  use an inexpensive external motor speed controller in this case.

* Bad motor.  Failures are possible but unless abused, not nearly as common
  as other simple problems like bad brushes or bearings.  It may not be cost
  effective to replace a bad armature or stator unless this is an expensive
  high quality drill or you have a similar model available for parts.

* Rusted or gummed up chuck. (Or, lost chuck key!).  The chuck is replaceable.
  Depending on type, it may mount with a right or left hand screw thread and
  possibly a right or left hand retaining screw through the center.  See the
  owner's manual to determine what your drill uses as you could be attempting
  to tighten rather than loosen the chuck if you turn the wrong way.  If by
  some slight chance you do not have the owner's manual :-), a reversible drill
  will usually have a left hand (reversed) thread on the chuck and a
  retaining screw with a right hand (normal) thread.  A non-reversible drill
  will only have a right hand thread on the chuck and probably no retaining
  screw.  There may be a hole to insert a locking rod to prevent the shaft
  from turning as you attempt to loosen the chuck.  Inserting the chuck key
  or a suitable substitute and gently tapping it with a hammer in the proper
  direction may be useful as well to free the chuck.

  A gummed up but not too badly rusted chuck can be rescued with penetrating
  oil like WD40 or Liquid Wrench: spray it into the chuck, let it sit for few
  minutes, then use the chuck key to start working it back and forth.  Pretty
  soon it should be free - rotate through its entire range back and forth.
  Spray and spin a couple more times and it should be fine for another 20.000

  8.9) Upgrading the bearings on a Craftsman drill

Very inexpensive models (like the $30 Father's day specials) may use sleeve
bearings in various locations instead of better quality longer lived ball or
roller bearings.  One particular bearing tends to deteriorate rapidly,
especially if the drill is used for sanding or in dusty work environments
(as opposed to clean rooms :-) ).  This is the motor bearing at the handle
end.  The lubrication dries out or is absorbed by dust particles, the bearing
runs dry, wears, and fails with an ear shattering squeal.  Even if you use ear
plugs, the speed and power are not adequate as the motor is laboring and
overloaded and motor failure would result from prolonged operation.

I have upgraded a couple of these drills to ball bearings.  The substitution
is straightforward requiring disassembly of the drill - removing of the
front gear reducer and then one side of the case.  At this point, the old
sleeve bearing is easily freed from its mounting (just the plastic of the
case) and pulled from the shaft.  The shaft is likely undamaged unless you
attempted to continue running the drill even after going deaf.

The drills I upgraded had bearings that were 7/8" OD, 5/16" thick, and with
a 5/16" ID center hole.  The old ones were worn by almost 1/32" oversize
for the center hole but the motor shaft was undamaged.  I found suitable
replacement double sealed ball bearings in my junk box but I would assume
that they are fairly standard - possibly even available from Sears Parts as
I bet they are used in the next model up.

If the gear reducer needs to come apart to access the motor, take note of
any spacer washers or other small parts so you can get them back in exactly
the correct locations.  Work in a clean area to avoid contaminating the
grease packing.

The bearing should be a press fit onto the shaft.  Very light sanding of
the shaft with 600 grit sandpaper may be needed - just enough so that the
new bearing can be pressed on.  Or, gently tap the center race with hammer
(protected with a block of wood).  Make sure that the bearing is snug when
mounted so that the outer race cannot rotate - use layers of thin heat
resistant plastic if needed to assure a tight fit (the old sleeve bearing
was keyed but your new ball bearing probably won't have this feature).

These drills now run as smoothly as Sears' much more expensive models.

  8.10) Cordless drills

Cordless drills use a permanent magnet DC motor operating off of a NiCd
(usually) battery pack.  Manufacturers make a big deal out of the voltage
of the pack - 6, 7.2, 9.6, 12, 14, 18, etc. - but this really isn't a sure
measure of power and time between charges as a motor can be designed for any
reasonable voltage.  A gear reducer follows the motor driving a chuck for
holding the drill or screwdriver bit, or attachment.  These are most often
have a single or two speeds with reverse.

In addition to the problems listed in the section: "AC line powered drills",
these are also subject to all the maladies of battery operated appliances.
Cordless tools are particularly vulnerable to battery failure since they
are often use rapid charge (high current) techniques.

* Bad NiCd batteries - reduced capacity or shorted cells.  In most cases,
  a new pack will be required.

* Bad power/speed selection/reversing switch.  Replace.

* Bad motor.  These are usually permanent magnet brushed type motors.
  Worn brushes and bearings are common problems.  In addition, a partially
  shorted motor due to commutator contamination is also possible - see the
  sections on PM DC motors.  Disassembly, cleaning, and lubrication may be

  8.11) Other direct drive tools

* Rotary (Moto) tools - high speed compact universal or PM motors with a
  variety of chucks and adapters for holding tiny bits, grinding stones,
  cutters, etc.

* Routers, biscuit cutters - high speed (30,000 RPM typical) universal
  motor with a 1/4" (fixed size, router) chuck for common router bits.

  Ball bearings are used which have long life but are probably replaceable
  if they fail (noisy, excessive runout, etc.).

  The plug, cord, trigger, and interlock switches are prone to problems and
  should be checked if the tool doesn't run at all.

* String trimmers - universal motor on long handle with trigger control.
  Check for a bad cord, switch, and dirt in the motor if the unit appears
  dead.  The motor brushes could also be worn or not seating properly.

  8.12) Saber saws, reciprocating saws

These use a universal motor which drives a gear reducer and reciprocating
mechanism.  Better models have a variable speed control so that the sawing
rate can be optimized to the work.  All but the most inexpensive allow the
head to be rotated or rotate automatically based on feed direction adding
a bit of complexity.

A reciprocating saw is very similar but uses a much larger motor and beefier

In addition to motor problems, there can be problems with damage, dirt, or
need for lubrication of the reciprocating mechanism.

  8.13) Electric chain saws

WARNING: Read and follow all safety instructions using any type of chain saw.

These have a high power universal motor and gear reducer.  Most have the
motor mounted transversely with normal pinion type gears driving the
chain sprocket.  A few models have the motor mounted along the axis of
the saw - I consider this less desirable as the gyroscopic character of
the rotating motor armature may tend to twist the saw as it is tilted
into the work.

Inexpensive designs suffer from worn (plain) bearings, particularly at the
end of the motor opposite the chain since this is exposed to the elements.
Normal maintenance should probably include cleaning and oiling of this
bearing.  A loud chattering or squealing with loss of speed and power is an
indication of a worn and/or dry bearing  Replacement with a suitable ball
bearing is also a possibility (see the section: "Upgrading the bearings on a Craftsman drill" since the approach is identical.

Keep the chain sharp.  This is both for cutting efficiency and safety.  A
dull chain will force you to exert more pressure than necessary increasing
the chance of accidents.  Chains can be sharpened by hand using a special
round file and guide or an electric drill attachment.  Alternatively, shops
dealing in chain saws will usually have an inexpensive chain sharpening
service which is well worth the cost if you are not equipped or not inclined
to do it yourself.

One key to long blade and bar life is the liberal use of the recommended
chain oil.  Inexpensive models may have a manual oiler requiring constant
attention but automatic oilers are common.  These are probably better - if
they work.  Make sure the oil passages are clear.

The chain tension should be checked regularly - the chain should be free to
move but not so loose that it can be pulled out of its track on the bar.  This
will need to snugged up from time-to-time by loosening the bar fastening nuts,
turning the adjustment screw, then retightening the nuts securely.

There may be a slip clutch on the drive sprocket to protect the motor if the
chain gets stuck in a log.  After a while, this may loosen resulting in
excessive slippage or the chain stopping even under normal conditions.  The
slip clutch can generally be tightened with a screwdriver or wrench.

  8.14) Circular saws, miter, and cutoff saws

These have a high power universal motor either directly driving the blade
or driving a gear reducer (high torque/large blade variety).

Miter and cutoff saws are similar but are mounted on a tilting mechanism
with accurate alignment guides (laser lights in the most expensive!).

  8.15) Grinding wheels

A dual shaft induction motor drives rotating grinding stones (or other tools
like wire brushes).  Most common are fixed speed - usually around 3450 RPM
but variable speed operation is highly desirable to avoid overheating of
tempered metal during sharpening.  All but the most inexpensive use sealed
ball bearings requiring no routine maintenance.

Small light duty grinders may be 1/4 HP or less.  However, this is adequate
for many home uses.

Wet wheels may run at much slower speeds to keep heat to a minimum.  Being
in close proximity to water may in itself create problems.

  8.16) Polishers, rotary sanders

A gear reduced universal motor drives a rubber (usually) mounting plate
to which a sanding disk or polishing pad is attached.

Due to the nature of their use, sanders in particular may accumulate a lot
of dust and require frequent cleaning and lubrication.

  8.17) Orbital sanders and polishers

In addition to the usual universal motor and its bearings, the orbital
mechanism may require cleaning and greasing periodically.

  8.18) Belt sanders, power planers

A typical portable belt sander uses a gear or belt reduced universal motor
driving one of the rollers that the sanding belt rotates on under tension.
In decent quality tools, these should use ball or roller bearings which require
little attention.

A power planer is similar in many ways but the motor drives a set of cutters
rather than a sanding belt.

  8.19) Air compressors

A direct or belt drive induction motor (probably capacitor start)
powers a single or multiple cylinder piston type compressor.  Typical
continuous motor ratings are between 1/4 and 2 HP (for a 115 VAC line).
Over and under pressure switches are used to maintain the pressure in
an attached storage tank within useful - and safe - limits.  Most will
include an unloading valve to remove pressure on the pistons when the
compressor stops so that it can be easily restarted without damage to
the motor and without blowing fuses or tripping circuit breakers.

I much prefer a belt driven compressor to a direct drive unit.  One
reason is that a motor failure does not render the entire compressor
useless as any standard motor can be substituted.  The direct drive
motor may be a custom unit and locating a replacement cheaply may be

Drain the water that collects in the tank after each use.

Inspect the tank regularly for serious rust or corrosion which could result
in an explosion hazard.as well.

  8.20) Paint sprayers

Traditional air powered paint sprayers may simply be an attachment to an
air compressor or may be a self contained unit with the compressor built in.
Since the active material is paint which dries into a hard mass (what a
concept!), cleaning immediately after use is essential.  Otherwise, strong
solvents will be needed to resurrect a congealed mess - check your user's
manual for acceptable deadly chemicals.

Portable airless paint sprayers use a solenoid-piston mechanism inside the
spray head itself.  There is little to go wrong electrically other than the
trigger switch as long as it is cleaned after use.

Professional airless paint sprayers use a hydraulic pump to force the
paint through a narrow orifice at extremely high pressure like 1000 psi.

With all types, follow the manufacturer's recommendations as to type and
thickness of paint as well as the care and maintenance before and after use
and for storage.

Warning: high performance paint sprayers in particular may be a safety
hazard should you put your finger close to the output orifice accidentally.
The pressures involved could be sufficient to inject paint - and anything
else in the stream - through the skin resulting in serious infection or worse.

  8.21) Heat guns

These are similar to high performance hair dryers and subject to the same
problems - bad cord or switch, open heating element, defective thermostats,
universal motor problems, and just plain dirt and dust buildup.

  8.22) Paint strippers

These are just a high power heating element attached to a cord.  If there
is no heat, check for a bad plug, cord, or open element with your multimeter.

  8.23) Soldering irons

Simple pencil irons use an enclosed heating element is attached to the
'business' end in some manner - screw thread, set screw, clamping ring,
etc.  Failure to heat may be due to a bad plug, cord, bad connections,
or defective element.

Some types package the heating element and replaceable tip in a separate
screw-in assembly.  These are easily interchangeable to select the
appropriate wattage for the job.  Damage is possible to their ceramic
insulator should one be dropped or just from constant use.

High quality temperature controlled soldering stations incorporate some
type of thermostatic control - possibly even with a digital readout.

  8.24) Soldering guns

The common Weller Dual Heat soldering gun is a simple transformer with the
tapped primary winding in the bulk of the case and a single turn secondary
capable of 100 or more amps at around 1.5 V.  The soldering element is simply
a piece of copper (possible with a shaped tip) which is heated due to the high
current passing through it even though it is made mostly of copper.  The
'headlight(s)' (flashlight bulbs) operate off of a winding on the transformer
as well.

Possible problems include:

* No response to trigger - bad cord, bad switch, open transformer primary.

* Low or high (dual heat models) does not work - bad switch, bad transformer

* Lack of sufficient heat - bad connections where soldering element mounts.
  clean and/or tighten.  Tin the tip if needed (not permanently tinned).
  Use the high setting (dual heat models).

* Tip too hot - use the lower setting (if dual heat).  Do not keep the trigger
  depressed for more than 30 seconds or so at a time.  Manually pulse width
  modulate the power level.

* Entire unit overheats - this could be a shorted winding in the transformer
  but more likely is that you are simply not giving it a chance to cool.  It
  is not designed for continuous operation - something like 2 minutes on, 5
  minutes off, is usually recommended.

* No light - bad bulbs, bad connections, bad winding (unlikely).

Note: a soldering gun is not a precision instrument and should not be used
for fine electronics work - you will ruin ICs and printed circuit boards.
(However, I have heard of someone replacing an MC68000 microprocessor (64 pin
DIP) successfully with a large Weller soldering gun!)

  8.25) Wet-dry vacs, yard blowers/vacs

A powerful universal motor driving a centrifugal blower is all there is
in this equipment.  Unfortunately, many common models use cheaply made
motors which may fail simply due to use or from the dust and proximity
to liquids.  The blower sucks air and whatever else into the holding tank.
A filter is supposed to prevent anything from getting through.  The motor
itself should be sealed against direct contact with the dust/liquid section
of the machine.

Problems occur with bad cords, switch, motor brushes, bearings, or a
burnt out motor from excessive use under adverse conditions.

As with inexpensive electric drills, sleeve bearings (usually, the top
bearing which is exposed somewhat) in the motor can become worn or dry.
Replacing with a ball bearing is a worthwhile - but rather involved -
undertaking if this happens.  See the section: "Upgrading the bearings on a Craftsman drill" as the technique is similar (once you gain access -
not usually a 10 minute job).

  8.26) Hedge trimmers

A gear reduced universal motor drives a reciprocating mechanism not too
dissimilar to a saber saw.  In addition to the usual motor/electrical
problems, lubrication may be needed periodically.  Should you accidentally
try to trim a steel fence instead of a bush, damage to one or more teeth
may occur.  In this case, light filing may be needed to remove nicks and

Of course, you probably will not get away without cutting the power cord
a couple of times as well!  See the sections on power cords.  One way to
avoid the humiliation (other than being half awake) is to wrap a cord
protector around the first 2 or 3 feet of cord at the tool.  This will
make the cord larger in diameter than the inter-tooth spacing preventing
accidental 'chewups'.

  8.27) Electric lawn mowers

A large universal or permanent magnet DC motor drives one or two sets of
rotating blades.  A load or dead short may be thrown across the motor to
act as a dynamic brake when stopping.  As usual, when the mower does not
operate, check for bad plug, cord, switch, brushes, dirt, etc.  See the
sections on motors.

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