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


  7.59) Drip coffee makers

A drip coffee maker consists of several components:

1. A heating element - combined or separate Calrod(tm, usually) types
   for operating the drip pump and then keeping the coffee warm.

2. Thermal protector - to prevent excess temperatures.

3. Some kind of water interlock - prevents dripping when separate reservoir
   is used.

4. Timer or controller.  The simplest are mechanical while programmable
   units with clocks and electronic timers are also available.

Many problems are be mechanical - clogged water passages or interlock.
Extended use with hard/high mineral content water can also result in reduced
heating effectiveness and/or increased heating times.  It may be possible to
flush the unit a couple of times with viniger.

If there is no heating, check the element and thermal protector with an
ohmmeter.  If the element is open, it is probably time for a new coffee maker.
The thermal protectors can be replaced but the underlying cause may be a
defective, shorted overheating element so it may not be worth the trouble.
Timers can develop bad contacts and bad connections are possible on electronic
controller circuit board wiring.

  7.60) Drop coffee maker repair

(From: Niels Henriksen (ap294@FreeNet.Carleton.CA)).

I wish I had thought of this sooner rather than throwing out the first 
coffee maker and I had planned to throw this one out.  For some reason I 
thought I would just look inside to see what was up.

Where I live the water is hard (well) and there is constant scaling and 
buildup of calcium.  We heard that all you have to do is to run a 
mixture of vinegar through the coffee maker to rejuvenate.

A friend and the 2 of ours all started to leak very badly when the 
vinegar/water mixture when through.  I though that the internal plumbing 
had corroded through the metal parts and the vinegar dissolved the 
calcium that was protecting the holes and therefore unrepairable. Who 
knows where these ideas come from.

Now for the technical solution.

The element that is used to boil the water and uses the bubbles to bring 
hot water to top of coffee maker is the same element that is used to 
keep the pot warm.

There is a metal tube attached to the metal warming element and this 
unit has a heating element embedded. There are 2 rubber hoses attached. 
One brings cold water to heater and the other brings boiling water to 
top. The cold water tube has a check valve that prevents the bubbling 
water from going to cold water reservoir.

When vinegar is added the calcium scales start to dissolve and in 3 of 3 
so far, this blocked the metal tube.  The water starts to boil and since 
the cold water inlet has a check valve the water pressure can only 
buildup to where the rubber tube is blown off the metal pipe.
No damage to parts.

To fix:

1. Take bottom off to gain access to heater area.

2. Remove rubber tubes which are connected with spring clamps.

3. Run rubber tubes through your fingers to loosen scale buildup and flush out

4. push a thin copper wire or other bendable wire through heating tube.  This
   is to unblock and loosen some scale.

5. Pour straight vinegar into metal tube to dissolve calcium and use wire to

6. Repeat several times till clean.

7. Re-attach all parts and use.

The solution is to start a regular process of using vinegar BEFORE the
calcium has buildup to the point where when loosened it will block the tube.

  7.61) Coffee percolators

While largely replaced by the drip coffee maker, these are still available,
particularly in large sizes.  The components are similar to those in a
drip coffee maker - element, thermal protector, possibly a thermostat
as well.  The element and bottom of the water/coffee container are likely
one piece to provide the best thermal conduction for the 'pump' in the
middle.  Even if the element is removable, it may not be worth the cost
of replacement except for a large expensive unit.

  7.62) Electric kettles

These consist of a heating element, thermal protector, and possibly a
thermostat and/or timer.  See comments for coffee makers.

  7.63) Electric (motor driven) clocks

While line operated clocks have mostly been superseded by electronic
(LED or LCD) clocks on nearly every kitchen appliance, many of these
are still in operation on older clock radios and ranges.

AC operated clocks depend on the AC line frequency (60 Hz or 50 Hz
depending on where you live) for time keeping.  The accuracy of a
line operated clock is better than almost any quartz clock since 
the long term precision of the power line frequency is a very carefully
controlled parameter and ultimately based on an atomic clock time standard.

Therefore, most problems are related to a clock motor that does not run or
will not start up following a power outage.  Once running, these rarely fail.

The most common problems are either gummed up oil or grease inside the
motor and gear train, broken gears, or broken parts of the clock mechanism
itself.  See the sections on "Synchronous timing motors" for repair info.

Battery operated quartz clocks usually operate on a 1.5 V Alkaline cell
(do not replace with NiCds as they do not have a long absolute life
between charges even if the current drain is small as it is with a clock).

First, test the battery.  Use a multimeter - usually anything greater than
1 V or so will power the clock though if it is closer to 1 V than 1.5 V,
the battery is near the end of its life.  The clock may run slow or fast
or erratically on a low battery.

With a good battery, failure to run properly is usually mechanical - one
of the hands is hitting against the glass front or something like that.
Don't forget to check any on/off switch - these are not expected but are
often present presumably to permit you to start the clock at precisely the
right time.  I had one case where the fine wire to the solenoid that
operates the once per second clock mechanism broke and had to be resoldered
but this is exceedingly rare.

If the clock consistently runs slow or fast with a known good battery,
there is usually a trimmer capacitor that can be adjusted with a fine
jeweler's straight blade screwdriver.  Without test equipment the best
you can do is trial and error - mark its original position and turn it
just a hair in one direction.  Wait a day or week and see if further
adjustment is needed (right, like you also won the lottery!) and fine
tune it.

If the hands should fall off (what a thought!), they can usually be pressed
back in place.  Then, the only trick is to line up the alarm hand with the
others so that the alarm will go off at the correct time.  This can usually
be done easily by turning the hour hand counterclockwise using the setting
knob in the rear until it is not possible to turn it further.  At this point,
it is lined up with the alarm hand.  Install all hands at the 12:00 position
and you should be more or less all set.

  7.64) Rotisseries

The mechanism consists of a shaded pole induction motor and gear train.
Clean and lubricate the gears.  See the section: "Shaded pole induction motors" for motor problems.

  7.65) Electric can openers and knife sharpeners

There consist of a shaded pole induction motor, gear train. and power
switch.  Likely problems relate to broken gear teeth, dirty or worn
power switch, dull cutting wheel, and broken parts.  Lubrication may
be needed if operation is sluggish.  Parts that come in contact with
the cans and lids collect a lot of food grime and should be cleaned

  7.66) Electric carving knives

A small motor operates a pair of reciprocating mounts for the blades.

AC powered carving knives include a momentary power switch, small motor
(probably universal type), and some gearing.  Congealed food goo as well
as normal lubrication problems are common.  The power switch is often
cheaply made and prone to failure as well.  The cord may be abused (hopefully
not cut or damaged by careless use of the knife!) and result in an intermittent
connection at one end or the other.  For motor problems, see the appropriate
sections on universal motors.

For battery powered knives, bad NiCds cells are a very likely possibility due
to the occasional use of this type of appliance.

See the section: "Small permanent magnet DC motors" and the chapter:
"Batteries" for information on repair.

  7.67) Electric scissors

Similar to electric carving knives except for the linkage to the blades.
All other comments apply.

  7.68) Portable and stationary food mixers

These consist of a universal motor which usually features a continuously
variable speed control or a selection of 3 to 5 speeds, a gearbox to transfer
power to the counter-rotating beaters, and a power switch (which may be
part of the speed control).

Sluggish operation may be due to cookie dough embedded in the gearing.  Fine
particles of flour often find their way into the gears - clean and lubricate.
There may be a specific relationship that needs to be maintained between
the two main beater gears - don't mess it up if you need to disassemble and
remove these gears or else the beaters may not lock in without hitting

The speed control may be a (1) selector switch, (2) mechanical control
on the motor itself, or (3) totally electronic.  Parts may be replaceable
although, for portables at least, a new mixer may make more sense.

For sluggish operation (non-mechanical), sparking, burnt smells, etc.,
see the section: "Problems with universal motors".

  7.69) Food processors

A powerful universal motor is coupled to interchangeable cutters of various
types.  In most respects, food processors are similar to any other universal
motor driven appliance with one exception: There will be a safety interlock
switch to prevent operation unless the cover is on properly and secured.  This
switch may go bad or its mechanical position adjustment may shift over time
resulting in difficulty in engaging power - or a totally dead unit.

As usual, cord and plug problems, bad bearings, burnt motor windings,
and broken parts are all possibilities.

  7.70) Steam and dry irons

Most modern irons (does anyone really use these anymore?) can be used
dry or with steam.

An iron consists of a sole plate with an integrated set of heating coils.

Steam irons will have a series of holes drilled in this plate along with
a steam chamber where a small amount of water is boiled to create steam.
A steam iron can be used dry by simply not filling its reservoir with water.
Those with a spray or 'shot of steam' feature provide a bypass to allow
hot water or steam to be applied directly to the article being ironed.

Over time, especially with hard water, mineral buildups will occur in the
various passages.  If these become thick enough, problems may develop.
In addition, mineral particles can flake off and be deposited on the

A thermostat with a heat adjustment usually at the top front of the
handle regulates the heating element.  This is usually a simple bimetal
type but access to the mechanism is often difficult.

Where an iron refuses to heat, check the cord, test the heating element
for continuity with your ohmmeter, and verify that the thermostat is

An iron that heats but where the steam or spray features are missing,
weak, or erratic, probably has clogged passages.  There are products
available to clear these.

Newer irons have electronic timeout controllers to shut the iron off
automatically if not used for certain amount of time as a safety feature.
Failure of these is not likely and beyond the scope of this manual in
any case.

When reassembling an iron, take particular care to avoid pinched or shorted
wires as the case is metal and there is water involved - thus a potential
shock hazard.

  7.71) Toasters

In addition to a fine heating element, there is a controller to determine
the length of time that the bread (or whatever) is heated.  A solenoid
or bimetal trip mechanism is used to pop the bread up (but hopefully not
totally out) of the toaster then it is 'done' and turn off the heating
element at the same time.

Since most of these are so inexpensive, anything more serious than a
broken wire or plug is probably not worth repairing.  The heating
element may develop a broken spot - particularly if something like a
fork is carelessly used to fish out an English muffin, for example.
(At least unplug it if you try this stunt - the parts may be electrically
live, your fork is metal, you are touching it!).  They may just go bad
on their own as well.

Being a high current appliance, the switch contacts take a beating
and may deteriorate or melt down.  The constant heat may weaken various
springs in either the switch contact or pop-up mechanism as well.
Sometimes, some careful 'adjustment' will help.

Controllers may be thermal, timer based, or totally electronic.  Except
for obvious problems like a bent bimetal element, repair is probably not
worth it other then as a challenge.

  7.72) Automatic toaster will not drop bread

If it really is old, then your problem is almost certainly mechanical -
a spring sprung or gummed up burnt raisin bread.  You will have to do
a little investigative research meaning: take the thing apart!  Try to
determine what the bread does to cause the support to drop down. It is
possible that putting the bread in is supposed to trip a microswitch which
activates a solenoid, and the switch or solenoid is now defective - bad
contacts or broken wires, bad coil in the solenoid, or grime.

The following applies directly to several Sunbeam models (and no doubt
to many others as well).

(From: John Riley (jriley@calweb.com)).

I will assume that the  toaster is either a model ATW or possibly an 
older model 20 or the like.

When you drop the bread in the toaster it trips a lever that is attached 
to the bread rack.  This lever pushes in on the contacts inside of the 
thermostat (color control switch) which actually turns the toaster on.
In "most cases" adjusting the screw on the bottom of the toaster will do 
the trick.  The proper adjustment is to adjust the carriage tension so 
that the bread rack in the side where it marked for a single slice of 
bread comes just to the uppermost limit of its travel.  Any more is 

If you have adjusted it as mentioned above and it still won't go down, 
there is one more thing you can try.  Take the toaster a sort of BUMP it 
down onto the table rather firmly.  Sometimes a piece of crumb will get 
in between the thermostat contacts.  A couple of good "bumps" on the 
table will usually dislodge the particle.

If all of the above doesn't work, and you know the cord isn't bad, them 
you may very well have a thermostat that has gone south.  They are still 
available for replacement on most models.  Suggest you check with your 
local SUNBEAM AUTHORIZED SERVICE for price and availability.

  7.73) Toaster oven (broilers)

I really liked the old original style GE toaster oven.  It was very versatile
and convenient for baking and toasting.  The newer types seem to have lost
some of these qualities.  The pop open door and oven tray have apparently
not been retained in any modern models that I am aware of.

Modern toaster oven (broilers) use Calrod style elements - usually two
above and two below the food rack.  Depending on mode, either just the
top (top brown/broil), just the bottom (oven), or both sets (toast) will
be energized.  Each pair may be wired in series meaning that a failure
of one will result in both of the pair being dead.  Very old units may
use a coiled NiChrome element inside a quartz tube.

Thermostats are usually of the bimetal strip variety with an adjustment
knob.  A cam or two on the shaft may also control main power and select
the broil function in the extreme clockwise position.

There may be a mode switch (bake-off-broil) which may develop bad contacts
or may fuse into one position if it overheats.  These are often standard
types and easily replaceable.  Just label where each wire goes on the
switch before removing it to take to an appliance repair parts store.

Newer models may use an electronic timer for the toast function at least.
I assume it is not much more than something like an IC timer (555) operating
the trip solenoid.  However, I have not had to deal with a broken one as

Testing is relatively straightforward.  Check the heating elements, thermostat,
mode switch,, cord, and plug.  While replacements for heating elements and
thermostats are often available, removing the old one and wiring the new one
may not be straightforward - rivets may be used for fastening and welds
for the wire connections.  You will have to drill the rivets with an electric
drill and replace them with nuts, bolts, and lockwashers.  Crimp splices
or nuts and bolts can be used for the wiring.  Take extra care in reassembly
to avoid any bare wires touching the metal cabinet or other parts as well as
insulation being cut by sharp sheetmetal parts.  The high temperature fiberglas
or asbestos insulation is not very robust.  In the end, it may not be
worth it with full featured toaster oven/broilers going for $20-30 on sale.

  7.74) Convection oven noise

Unlike a regular (non-microwave) oven, convection ovens are not totally
silent.  There is a small fan used to circulate the hot air (thus the
name: convection oven).  Depending on the oven's design and age, these
fans may be anywhere from nearly silent to objectionably noisy.

If you notice an increase in motor noise (whining or squealing, grinding,
knocking) then the motor and fan should be inspected and parts replaced
if necessary.  Sudden failure is unlikely but if it were to happen - seized
bearings, for example - an overtemperature thermal protector should shut
down the heating element or entire oven.  Some of these may not be self
resetting (thermal fuse).

  7.75) Hot plates, waffle irons, broilers, deep friers, rice and slow cookers, woks

These are all just a single or dual heating element, thermal protector
(not all will have one), and an adjustable (usually) thermostat.  As usual,
check the cord and plug first, and then each of the other parts with an

Where a NiChrome coil type heating element is used, a break will be obvious.
If it is very near one end, then removing the short section and connecting the
remainder directly to the terminal will probably be fine.  See the section:
"Repair of broken heating elements".

For appliances like waffle irons, burger makers, and similar types with
two hinged parts, a broken wire in or at the hinge is very common.

Note that since these operate at high temperatures, special fiberglass (it
used to be asbestos) insulated wiring is used.  Replace with similar types.
Take extra care in reassembly to avoid shorted wires and minimize the handling
and movement of the asbestos or fiberglas insulated high temperature wiring.

  7.76) Popcorn poppers (oil type)

An Oil popper is basically an electric frying pan with a built-in stirrer and
cover.  The internal parts are accessed from the bottom: Heating coil,
thermostat and thermal protector, and small gear-motor similar to that used
in a clock or timer.  Take care to note the orientation of the motor when
removing and to not damage any seals (you don't want oil seeping down under!).

As always, check for bad connections if the popper is dead or operation is

Problems with heating can arise in the heating element, thermostat, and
thermal protector.

If the stirrer doesn't turn, a gummed up motor or stirrer shaft (since these
are only used occasionally) may be the problem.  See the chapter: "Motors 101".

  7.77) Popcorn poppers (air type)

Air poppers combine a heating element and blower to heat corn kernels without
the need for any unhealthy oil.  Of course, you probably then drown the popcorn
in butter and salt, huh?  Admit it! :-).

As always, check for bad connections if the popper is dead or operation is

Problems with heating can arise in the heating element, thermostat, and
thermal protector.

The motor is probably a small PM DC type and there will then be a set of
diodes or a bridge rectifier to turn the AC into DC.  Check these and for
bad bearings, gummed up lubrication, or other mechanical problems if the
motor does not work or is sluggish.  See the chapter: "Motors 101".

  7.78) Sewing machines

Moth mechanical and electrical problems are possible.  (Note: we are not
going to deal with fancy computerized equipment as this is probably better
left to a professional except for the more obvious problems like a bad
cord or plug.)

I have a 1903 Singer foot-pumped sewing machine which we have since electrified
and still runs fine.  A couple of drops of sewing machine or electric motor
oil every so often is all that is needed.  They were really built well back

Although the appearance of the internal mechanism may appear intimidating
at first, there really is not that much to it - a large pulley drives a
shaft that (probably) runs the length of the machine.  A few gears and
cams operate the above (needle and thread) and below (feet and bobbin)
deck mechanisms.  Under normal conditions, these should be pretty robust.
(Getting the adjustments right may be another story - refer to your users
manual).  Sometimes if neglected, the oil may seriously gum up and require
the sparing use of a degreaser to loosen it up and remove before relubing.

If the motor spins but does not turn the main large pulley, the belt is
likely loose or worn.  The motor will generally be mounted on a bracket
which will permit adjustment of the belt tension.  The belt should be tight
but some deflection should still occur if you press it gently in the middle.

If the motor hums but nothing turns, confirm that the belt is not too tight
and/or that the main mechanisms isn't seized or overly stiff - if so, it
will need to be cleaned and lubrication (possibly requiring partial

The electric motor is normally a small universal type on a variable speed
foot pedal (see the section: "Wiring a sewing machine speed control").

If the motor does not work at all, bypass the foot pedal control to confirm
that it is a motor problem (it is often possibly to just plug the motor
directly into the AC outlet).  Confirm that its shaft spins freely.  All
normal motor problems apply - bad wiring, worn brushes, open or shorted
windings, dirty commutator.  See the section: "Problems with universal motors".

  7.79) Wiring a sewing machine speed control

This assumes a basic sewing machine (nothing computer controlled) with
a normal universal series wound motor (115 VAC).

The common foot pedals are simply wirewound rheostats (variable resistors)
which have an 'off' position when the pedal is released.  They are simply
wired in series with the universal motor of the sewing machine (but not
the light) and can be left plugged in all the time (though my general
recommendation as with other appliances is to unplug when not in use.

While not as effective as a thyristor type speed controller, these simple
foot pedals are perfectly adequate for a sewing machine.  There are also
fancier speed controls and using a standard light dimmer might work in some
cases.  However, there are two problems that may prevent this: the sewing
machine motor is a very light load and it is a motor, which is not the same
as a light bulb - it has inductance.  The dimmer may not work, may get stuck
at full speed, or may burn out.

  7.80) Shavers

A variety of types of drive mechanisms are used in electric shavers:

1. Vibrator (AC only) - these (used by Remington among others) consist of
   a moving armature in proximity to the pole pieces of an AC electromagnet.
   The mass and spring are designed so that at the power line frequency, the
   armature vibrates quite strongly and is linked to a set of blades that
   move back and forth beneath the grille.

   If dead, check for continuity of the plug, cord, switch, and coil.  IF
   sluggish, clean thoroughly - hair dust is not a good lubricant.  Sliding
   parts probably do not require lubrication but a drop of light oil should
   be used on any rotating bearing points.

   Note that since a resonance is involved, these types of shavers may not
   work well or at all on foreign power - 50 Hz instead of 60 Hz or vice
   versa - even if the voltage is compatible.

2. Universal motor (AC or DC) - very small versions of the common universal
   motors found in other appliances.  A gear train and linkage convert the
   rotary motion to reciprocating motion for shavers with straight blades or
   to multiple rotary motion for rotary blade shavers.  These may suffer
   from all of the afflictions of universal motors; bad cords, wires, and
   switches; and gummed up, clogged, or worn mechanical parts.  Also see
   the sections on the appropriate type of motor.  Take care when probing
   or disassembling these motors - the wire is very fine any may be easily
   damaged - I ruined an armature of a motor of this type by poking where
   I should not have when it was running - ripped all the fine wires from
   the commutator right off.

3. DC PM motor - often used in rechargeable shavers running of 2 or 3 NiCd
   cells.  These may suffer from battery problems as well as motor and
   mechanical problems.  One common type is the Norelco (and clone) rotary
   shaver.  See the chapters on Batteries and AC Adapters as well as the
   sections on "Small permanent magnet DC motors".

   A shaver that runs sluggishly may have a dead NiCd cell - put it on
   charge for the recommended time and then test each cell - you should
   measure at least 1.2 V.  If a NiCd cell reads 0, it is shorted and
   should be replaced (though the usual recommendation is to replace all
   cells at the same time to avoid problems in the future).

   Note that in terms of rechargeable battery life, shavers are just about
   optimal as the battery is used until it is nearly drained and then 
   immediately put on charge.  The theoretical 500 to 1000 cycle NiCd life
   is usually achieved in shaver applications.

  7.81) Electric toothbrushes

These are basically similar to any other small battery operated appliance or
tool such as a screwdriver or drill.  The permanent magnet motor runs off of
rechargeable NiCd batteries and cause the bristles or whatever to oscillate,
rotate, or vibrate.  Interchangeable 'brush' units allow each member of the
family to have their own.

Problems can occur in the following areas:

* Motor, battery pack, connections, on/off switch - as with any other similar

* Power train - gummed up lubrication, broken, or other mechanical problems.

* Charging station or circuitry - the fault may be with the base unit or
  circuitry associated with the battery pack.  See the section: "Braun electric toothbrush repair", below.

Since these must operate in a less than ideal environment (humid or actual
waterlogged!), contamination and corrosion is quite possible if the case is
not totally sealed.  Some of the switched may be of the magnetic reed type so
that there don't need to be any actual breaks in the exterior plastic housing.

Of course, getting inside may prove quite a challenge:

(From: Jeff & Sandy Hutchinson (sandy2@flatoday.infi.net)).

It's darned near impossible to replace the batteries on the Interplak
toothbrush without destroying the recharging circuit.  The base of the hand
unit has a little pickup coil in it, and when you unscrew the cap to get at
the batteries, you break the connections to the pickup coil.  Best to do an
exchange with the factory.

  7.82) Braun electric toothbrush repair

(From: David DiGiacomo (dd@Adobe.com)).

This Braun electric toothbrush (original model) would turn itself on and keep
running until its batteries were discharged.

The toothbrush can be disassembled by pulling the base off with slip joint
pliers (do not pull too hard because there is only about 1" of slack in
the charging coil wires).  With the base off, the mechanism slides out of
the case.

There is a simple charging circuit, charging LED, 2 NiCd cells, and a reed
switch driving the base of an NPN transistor.  The transistor collector
drives the motor.

I charged the battery, but the problem of the motor running with the reed
switch open didn't recur until I held my finger on the transistor for
about 10 seconds seconds.  Grounding the transistor base turned it off
again, and I could repeat this cycle.  Since there wasn't anything else to
go wrong I decided to replace the transistor.  I couldn't read the
marking, but it's in a SOT89 package and the motor current is 400-700 mA so
it must be something like a BC868.  However, I didn't have any surface
mount or TO92 transistors that could handle the current, so I used a
2SD882 (small power tab package), which I was able to squeeze into some
extra space in the center of the charging coil.

  7.83) Hand massagers

These are simply motors with an off-axis (eccentric) weight or electromagnetic
vibrators.  If the unit appears dead, check the plug, cord, on/off switch,
internal wiring, and motor for continuity.  Confirm that the mechanical parts
turn or move freely.

Some have built in infra-red heat which may just be a set of small light
bulbs run at low voltage to provide mostly heat and little light (a filter
may screen out most of the light as well).  Obviously, individual light
bulbs can go bad - if they are wired in series, this will render all of
them inert.

At least one brand - Conair - has had problems with bad bearings.  Actually,
poorly designed sleeve bearings which fail due to the eccentric load.  If you
have one of these and it becomes noisy and/or fails, Conair will repair
(actually replace) it for $5 if you complain in writing and send it back to
them.  They would like a sales receipt but this apparently is not essential.

  7.84) Hair dryers and blow dryers

A heating element - usually of the NiChrome coil variety - is combined with
a multispeed centrifugal blower.

First determine if the problem is with the heat, air, or both.

For heat problems, check the element for breaks, the thermal protector
or overtemperature thermostat (usually mounted in the air discharge), the
connections to the selector switch, and associated wiring.

For air problems where the element glows but the fan does not run, check the
fan motor/bearings, connections to selector switch, and associated wiring.
Confirm that the blower wheel turns freely and is firmly attached to the
motor shaft.  Check for anything that may be blocking free rotation if the
blower wheel does not turn freely.  The motor may be of the induction,
universal, or PM DC type.  For the last of these, a diode will be present
to convert the AC to DC and this might have failed.  See the appropriate
section for problems with the type of motor you have.

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