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


  5.3) Safety guidelines

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
  short to.  Hold them in place with string or electrical tape.  Prop them
  up with insulation sticks - plastic or wood.

* Parts of heating appliances can get very hot very quickly.  Always carefully
  test before grabbing hold of something you will be sorry about later.

* 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.  Even with
  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
  example.  (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!

  5.4) Should I unplug appliances when not in use?

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
damage.  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.

  5.5) Troubleshooting tips

Many problems have simple solutions.  Don't immediately assume that
your problem is some combination of esoteric complex convoluted
failures.  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.  Etc.  Etc.

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.

  5.6) Basic hand tools

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
at times.

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: "Soldering techniques".

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: "Solderless connectors".

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.

  5.7) Soldering techniques

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.  Use of the
proper technique is critical to reliability and safety.  A good 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.

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.  Suggested
  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
  board work; 25-50 W iron for general soldering of terminals and wires
  and power circuit boards; 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,
  etc.  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.  The
  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!

  5.8) Desoldering techniques

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
action; rubber bulb type solder pumps, and motor driven vacuum solder
rework stations (pricey).

See the document: "Troubleshooting and Repair of Consumer Electronics
Equipment" for additional info on desoldering of electronic components.

  5.9) Soldering pins in plastic connectors

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.  In some
cases, a larger iron is better - you get in and out more quickly without
heating up everything in the neighborhood.

  5.10) Solderless connectors

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.  For
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.  One
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
function.  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.  It is
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.  The
  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.

  5.11) Wire stripping

In order to make most connections, the plastic or other insulating covering
must be removed to expose the bare copper conductors inside.  The best
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.

  5.12) Attaching wires to screw terminals

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:

1. 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).  For most
   applications, this is satisfactory.

2. Avoid the temptation to put multiple wires around a single terminal
   unless you separate each one with a flat washer.

3. 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 might short to something;
   too little and a firm mechanical joint and electrical connection may be

4. For multistranded wire, tightly twist the strands of stripped wire together
   in a clockwise direction as viewed from the wire end.

5. 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.

6. 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.

7. 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.

  5.13) Test equipment

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).  Your
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:

1. 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
   tester.   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.

2. Outlet tester (grounds and miswiring) - This will confirm that a 3 prong
   outlet is correctly wired with respect to Hot, Neutral, and Ground.  While
   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
   current).  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.

3. 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
   probes.  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.

4. 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.  Insulate
   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.

5. 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
   reason.  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: "Phantom voltage measurements of electrical wiring".

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.

  5.14) Getting inside consumer electronic equipment

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:

1. Screws.  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.

2. 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.  For
   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.

3. Snaps.  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.

4. Glue.  Or more likely, the plastic is fused together.  This is 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

5. 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.

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.  I often
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.

  5.15) Getting built up dust and dirt out of a equipment

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 disturbing anything excessively.  Some
gentle blowing (but no high pressure air) may be helpful in dislodged
hard to get at dirt - but wear a dust mask.

Don't use compressed air on intricate mechanisms, however, as it might
dislodge dirt and dust which may then settle on lubricated parts and 
contaminating them.  High pressure air could move oil or grease from where
it is to where it should not be.  If you are talking about a shop air
line, the pressure may be much much too high and there may be contaminants
as well.

A Q-tip (cotton swab) moistened with politically correct alcohol can be used
to remove dust and dirt from various hard to get at surfaces.

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