Notes on the Troubleshooting and Repair of Microwave Ovens


[Document Version: 3.11] [Last Updated: 05/25/1998]

Chapter 1) About the Author & Copyright

Notes on the Troubleshooting and Repair of Microwave Ovens

Author: Samuel M. Goldwasser
Corrections/suggestions: | Email

Copyright (c) 1994, 1995, 1996, 1997, 1998
All Rights Reserved

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

  1. This notice is included in its entirety at the beginning.
  2. There is no charge except to cover the costs of copying.

Chapter 2) Introduction

Radar Range anyone?

Remember when you actually had to use the real oven to defrost a TV
dinner?  Think back - way back - before VCRs, before PCs (and yes, before
Apple computers as well), almost before dinosaurs, it would seem.  There
was a time when the term 'nuke' was not used for anything other than bombs
and power reactors.

For a long time, there was controversy as to whether microwave ovens were
safe - in terms of microwave emissions and molecular damage to the food.
Whether these issues have been resolved or just brushed aside is not totally
clear.  Nonetheless, the microwave oven has taken its place in virtually
every kitchen on the planet.  Connoisseurs of fine dining will turn up
their collective noses at the thought of using a microwave oven for much
beyond boiling water - if that.  However, it is difficult to deny the
convenience and cooking speed that is provided by this relatively simple

Microwave ovens are extremely reliable devices.  There is a good chance
that your oven will operate for 10 years or more without requiring repairs
of any kind - and at performance levels indistinguishable from when it
was first taken out of the box.  Unlike other consumer electronics
where a new model is introduced every 20 minutes - some even have useful
improvements - the microwave oven has not changed substantially in the
last 20 years.  Cooking is cooking.  Touchpads are now nearly universal
because they are cheaper to manufacture than mechanical timers (and also
more convenient).  However, an old microwave oven will heat foods just
as well as a brand new one.

This document provides maintenance and repair information applicable to
most of the microwave ovens in existence.  It will enable you to quickly
determine the likely cause and estimate the cost of parts.  You will be
able to make an informed decision as to whether a new oven is the better
alternative.  With minor exceptions, specific manufacturers and models will
not be covered as there are so many variations that such a treatment would
require a huge and very detailed text.  Rather, the most common problems
will be addressed and enough basic principles of operation will be provided
to enable you to narrow the problem down and likely determine a course of
action for repair.  In many cases, you will be able to do what is required
for a fraction of the cost that would be charged by a repair center - or - be
able to revive something that would otherwise have gone into the dumpster
or continued in its present occupation as a door stop or foot rest.

Should you still not be able to find a solution, you will have learned a great
deal and be able to ask appropriate questions and supply relevant information
if you decide to post to sci.electronics.repair.  In any case, you will have
the satisfaction of knowing you did as much as you could before taking it in
for professional repair.  You will be able to decide if it is worth the cost
of a repair as well.  With your new-found knowledge, you will have the upper
hand and will not easily be snowed by a dishonest or incompetent technician.

  2.1) On-line microwave oven repair database

Microtech maintains a web site with a large amount of information on microwave
oven repair including an on-line Tech Tips Database with hundreds of solutions
to common problem for many models of microwave ovens.  There are also an
extensive list of microwave oven related links to other interesting sites
(including this document!).  The comprehensive Safety Info is a must read
as well.  Microtech also offers instructional videos and books on microwave
oven and VCR repair.

It is quite possible your problem is already covered at the Microtech site.
In that case, you can greatly simplify your troubleshooting or at least
confirm a diagnosis before ordering parts.  My only reservation with respect
to tech tips databases in general - this has nothing to do with Microtech
in particular - is that symptoms can sometimes be deceiving and a solution
that works in one instance may not apply to your specific problem.  Therefore,
an understanding of the hows and whys of the equipment along with some good
old fashioned testing is highly desirable to minimize the risk of replacing
parts that turn out not to be bad.

  2.2) Expert system for microwave oven fault diagnosis

The MIDES (Microwave Oven Diagnosis Expert System) site represents an
interesting and possibly useful approach for isolating the cause of many common
failures.  It will take you through a customized step-by-step procedure based
on your symptoms (and specific microwave oven model in some cases) and the
results of its suggested tests.  For the novice, this may be an effective way
of obtaining a solution quickly as long as you follow the extremely important
safety information provided by MIDES (or this document).  You will not be
forced to acknowledge that you have read, understood, and followed their safety
precautions and warnings before performing each test.

  2.3) The simplest problems

* Bad interlocks switches or door misalignment causing fuses to blow or no
  operation when the start button is pressed.  Locate and replace defective
  switches and/or realign door.

* Arcing in oven chamber: clean oven chamber and waveguide thoroughly.  Replace
  carbonized or damaged waveguide cover.  Smooth rough metal edges.  Touch
  up the interior paint.

* Blown fuse due to power surge or old age:  Replace fuse.  On rare occasions,
  the main fuse may even be intermittent causing very strange symptoms.

* Erratic touchpad operation due to spill - let touchpad dry out for a week.

* Bugs in the works - the controller circuit board is a nice warm safe cozy
  place to raise a family.....

More detailed explanations are provided elsewhere in this document.

  2.4) Repair or replace?

With small to medium size microwave ovens going for $60-100 it hardly makes
sense to spend $60 to have one repaired.  Even full size microwave ovens with
full featured touchpanel can be had for under $200.  Thus, replacement
should be considered seriously before sinking a large investment into an
older oven.

However, if you can do the repair yourself, the equation changes dramatically
as your parts costs will be 1/2 to 1/4 of what a professional will charge
and of course your time is free.  The educational aspects may also be
appealing.  You will learn a lot in the process.  Many problems can be
solved quickly and inexpensively.  Fixing an old microwave for the dorm
room may just make sense after all.

Chapter 3) Installation and Preventive Maintenance

  3.1) Microwave oven installation and use

To assure safety and convenient, follow these recommendations:

* Read your users manual from cover to cover especially if this is your first
  microwave.  What a concept!  If nothing else, you may discover that your
  oven has features you were not aware were even possible.  In any case, there
  may be requirements or suggestions that are specific to your model and will
  enable you to get the most performance from your new microwave.

* Select a stand-alone unit rather than a built-in if possible.  It will be
  cheaper to buy, cheaper and easier to service, and possibly more reliable
  since ventilation and adjacent heat producing appliances will not be as
  much of a factor.

* Select a convenient location - easy access and not too high or too low.
  This is particularly important if the door of the oven opens down instead
  of to the left side (only a few models are built this way, however).

* Put the microwave oven on its own dedicated 3 wire grounded circuit.
  Temporary use of a 3 to 2 prong adapter is acceptable only if the outlet
  box is properly grounded to begin with (BX, Romex, or conduit with ground).

  Make sure the outlet is in good condition in either case.  Check that the
  plug (or adapter) fits tightly and that there is no appreciable heating
  of the outlet during use of the microwave oven.  If there is, spread the
  metal strips of each of the prongs apart if possible and/or replace the

  A grounded outlet is essential for safety.  Microwave ovens are high
  power devices and a separate circuit will eliminate nuisance fuse blowing
  or circuit breaker tripping when multiple appliances are being used at
  the same time.  It will also minimize the possibility of Radio Frequency
  Interference (RFI) between it and any electronic equipment which might be
  on the same circuit.  A GFCI is not needed as long as the outlet is properly
  grounded and may result in nuisance tripping with some microwave ovens.

  Inexpensice outlet testers are available at hardware stores, home centers,
  and electrical parts distributors, to confirm that the outlet is properly
  wired and grounded.

* Allow adequate ventilation - do not push it up against the wall or wedge
  it under a tight fitting wall cabinet (or inside one for that matter!).
  Leave at least 2 inches on all sides and top if possible.

* Do not let children use the microwave oven unless properly supervised.  It
  is very easy to cause a fire through the use of excessive times or power
  settings.  Even something as simple as microwave popcorn can explode and/or
  catch fire if heated for too long - e.g., 5 minutes instead of my precisely
  determined 3:41 on high :-).

  3.2) Microwave oven maintenance

Most people do not do anything to maintain a microwave oven.  While not
much is needed, regular cleaning at least will avoid potentially expensive
repairs in the future:

* Clean the interior of the oven chamber after use with a damp cloth and some
  detergent if necessary.  Built up food deposits can eventually carbonize
  resulting in sparks, arcs, heating, and damage to the mica waveguide cover
  and interior paint - as well as potentially more serious damage to the
  magnetron.  If there is any chance of food deposits having made their way
  above the waveguide cover in the roof of the chamber, remove the waveguide
  cover and thoroughly clean inside the waveguide as well.

* Clean the exterior of the cabinet and touchpad in a similar manner.  DO NOT
  use a spray where any can find its way inside through the door latch or
  ventilation holes, or a dripping wet cloth.  Be especially careful around
  the area of the touchpad since liquid can seep underneath resulting in
  unresponsive or stuck buttons or erratic operation.  Do not use strong
  solvents (though a bit of isopropyl alcohol is fine if needed to remove
  sticky residue from unwanted labels, for example).

* Inspect the cord and plug for physical damage and to make sure the
  plug is secure and tight in the outlet - particularly if the unit is
  installed inside a cabinet (yes, I know it is difficult to get at but
  I warned you about that!).  Heat, especially from a combination
  microwave/convection oven or from other heat producing appliances
  can damage the plug and/or cord.  If there is evidence of overheating at
  the outlet itself, the outlet (and possibly the plug as well) should be

* Periodically check for built up dust and dirt around the ventilation
  holes or grills.  Clean them up and use a vacuum cleaner to suck up
  loose dust.  Keeping the ventilation free will minimize the chance of

* Listen for any unusual sounds coming from inside the oven.  While these
  appliances are not exactly quiet, grinding, squealing, scraping, or other
  noises - especially if they were not there when the oven was new - may
  indicate the need for some more extensive maintenance like belt replacement
  or motor lubrication.  Attending to these minor problems now may prevent
  major repairs in the future.

* Keep your kitchen clean.  Yes, I know, this isn't exactly microwave
  specific but cockroaches and other uninvited guests might just like to
  take up residence inside the electronics bay of the oven on the nice warm
  controller circuit board or its neighborhood and they aren't generally
  the tidiest folks in the world.

  If it is too late and you have a recurring problem of cockroaches getting
  inside the electronics bay, tell them to get lost and then put window screen
  over the vents (or wherever they are entering).  Such an open mesh should
  not affect the cooling of the electronic components significantly.  However,
  the mesh will likely clog up more quickly than the original louvers so make
  sure it is cleaned regularly.  If possible, clean up whatever is attracting
  the unwanted tenants (and anything they may have left behind including their
  eggs!!).  WARNING: See the section: "SAFETY" before going inside.

CAUTION: Do not spray anything into the holes where the door latch is inserted
or anywhere around the touchpad as this can result in internal short circuits
and costly damage - or anywhere else inside, for that matter.  If you do this
by accident, immediately unplug the oven and let it dry out for a day or two.

  3.3) How long does microwave energy hang around?

You have probably been warned by your mother: "Wait a few seconds (or minutes)
after the beep for all the microwaves to disappear".  There is no scientific
basis for such a recommendation.  Once the beep has sounded (or the door has
opened), it is safe.  This is because:

1. There is no such thing as residual microwave radiation from a microwave
   oven - it is either being produced or is non-existent.

2. There is little energy storage in the microwave generator compared to
   the amount being used.  The typical high voltage capacitor - the only
   component that can store energy - has a capacity of less than 15 W-s
   (Watt-seconds) even for the largest ovens.  Power consumption is typically
   800 to 1500 W depending on oven size.  Therefore, the capacitor will be
   fully drained in much less than .1 second - long before the beep has ended
   or the door has cleared the front panel.  (Based on the numbers, above, for
   a 1500 W oven with a capacitor storing 15 W-s, it is more like .01 seconds!)

   WARNING: This only applies to a *working* microwave oven!  If there is no
   heat, the magnetron may not be drawing any current from the HV power
   supply and the HV capacitor can remain charged for a long time.  In this
   case, there is a very real risk of potentially lethal electrical shock even
   after several minutes or more of being unplugged!  See the section:
   "SAFETY" if you will be troubleshooting a microwave oven.

Chapter 4) Microwave Oven Troubleshooting

  4.1) SAFETY


Microwave ovens are probably the most dangerous of consumer appliances
to service.  Very high voltages (up to 5000 V) at potentially very high
currents (AMPs) are present when operating - deadly combination.  These
dangers do not go away even when unplugged as there is an energy storage
device - a high voltage capacitor - that can retain a dangerous charge
for a long time.  If you have the slightest doubts about your knowledge
and abilities to deal with these hazards, replace the oven or have it
professionally repaired.

Careless troubleshooting of a microwave oven can not only can fry you from
high voltages at relatively high currents but can microwave irradiate you as
well.  When you remove the metal cover of the microwave oven you expose
yourself to dangerous - potentially lethal - electrical connections.  You
may also be exposed to potentially harmful levels of microwave emissions if
you run the oven with the cover off and there is damage or misalignment to
the waveguide to the oven chamber.

There is a high voltage capacitor in the microwave generator.  Always ensure
that it is totally discharged before even thinking about touching or probing
anything in the high voltage power circuits.  See the troubleshooting sections
later in this document.

To prevent the possibility of extremely dangerous electric shock, do not
operate the oven with the cover off if at all possible.  If you must probe
live, remove the connections to the magnetron (see below) to prevent the
inadvertent generation of microwaves except when this is absolutely needed
during troubleshooting.  Discharge the high voltage capacitor and then use
clip leads to make any connections before you apply power to the oven.

The microwave oven circuitry is especially hazardous because the return for
the high voltage is the chassis - it is not isolated.  In addition, the HV
may exceed 5000 V peak with a continuous current rating of over .25 AMP at
50/60 Hz - the continuous power rating of the HV transformer may exceed
1500 W with short term availability of much greater power.  Always observe
high voltage protocol.

  4.2) Safety guidelines

These guidelines are to protect you from potentially deadly electrical shock
hazards as well as the equipment from accidental damage.

Note that the danger to you is not only in your body providing a conducting
path, particularly through your heart.  Any involuntary muscle contractions
caused by a shock, while perhaps harmless in themselves, may cause collateral
damage - there are many sharp edges inside this type of equipment as well as
other electrically live parts you may contact accidentally.

The purpose of this set of guidelines is not to frighten you but rather to
make you aware of the appropriate precautions.  Repair of TVs, monitors,
microwave ovens, and other consumer and industrial equipment 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.

* 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: TVs and monitors may use parts of the metal chassis
  as ground return yet the chassis may be electrically live with respect to the
  earth ground of the AC line.  Microwave ovens use the chassis as ground
  return for the high voltage.  In addition, do not assume that the chassis
  is a suitable ground for your test equipment!

* If circuit boards need to be removed from their mountings, put insulating
  material between the boards and anything they may short to.  Hold them in
  place with string or electrical tape.  Prop them up with insulation sticks -
  plastic or wood.

* If you need to probe, solder, or otherwise touch circuits with power off,
  discharge (across) large power supply filter capacitors with a 25 W or
  greater resistor of 5 to 50 ohms/V approximate value.

  For the microwave oven in particular, use a 25K to 100K 25 W resistor with
  a secure clip lead to the chassis.  Mount the resistor on the end of a well
  insulated stick.  Touch each of the capacitor terminals to the non-grounded
  end of the resistor for several seconds.  Then, to be doubly sure that the
  capacitor if fully discharged, short across its terminals with the blade of
  a well insulated screwdriver.  I also recommend leaving a clip lead shorting
  across the capacitor terminals while working as added insurance.  At most,
  you will blow a fuse if you should forget to remove it when powering up the

* 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.

* 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.

* Perform as many tests as possible with power off and the equipment unplugged.
  For example, the semiconductors in the power supply section of a TV or
  monitor can be tested for short circuits with an ohmmeter.

* 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.  A circuit breaker is too slow and insensitive to provide any
  protection for you or in many cases, your equipment.  A GFCI may, however
  prevent your scope probe ground from smoking should you accidentally connect
  an earth grounded scope 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!

As noted, a GFCI (Ground Fault Circuit Interrupter) will NOT protect you
from the high voltage since the secondary of the HV transformer is
providing this current and any current drawn off of the secondary
to ground will not be detected by the GFCI.  However, use of a GFCI is
desirable to minimize the risk of a shock from the line portions
of the circuitry if you don't have an isolation transformer.

An isolation transformer is even limited value as well since the chassis IS
the HV return and is a large very tempting place to touch, lean on, or brush
up against.

And, of course, none of these devices will protect fools from themselves!

Take extreme care whenever working with the cover off of a microwave oven.

  4.3) Troubleshooting tips

Many problems have simple solutions.  Don't immediately assume that
your problem is some combination of esoteric complex convoluted
failures.  For a microwave oven, there may be a defective door
interlock switch or just a tired fuse.

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 (particularly with microwave ovens) and mostly non-productive
(or possibly destructive - very destructive).

If you need to remove the cover or other disassembly, make notes of which
screw went where - they may not all be identical.  More notes is better
than less.

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 for storage.

A basic set of high quality hand tools will be all you need to work on a
microwave oven.   These do not need to be really expensive but poor quality
tools are worse than useless and can cause damage.  Stanley or Craftsman
are fine.  Needed tools include a selection of Philips and straight blade
screwdrivers, needlenose pliers, wire cutters and wire strippers.

A medium power soldering iron and rosin core solder (never never use acid
core solder or the stuff for sweating copper pipes on electronic equipment)
will be needed if you should need to disconnect any soldered wires (on
purpose or by accident) or replace soldered components.

However, most of the power components in microwave ovens use solderless
connectors (lugs) and replacements usually come with these as well.

See the document: "Troubleshooting and Repair of Consumer Electronics
Equipment" for additional info on soldering and rework techniques and
other general information.

An assortment of solderless connectors (lugs and wirenuts) is handy when
repairing the internal wiring.  A crimping tool will be needed as well but
the $4 variety is fine for occasional use.

Old dead microwaves can often be valuable source of hardware and sometimes
even components like interlock switches and magnetrons as these components
are often interchangeable.  While not advocating being a pack rat, this
does have its advantages at times.

  4.4) Test equipment

Don't start with the electronic test equipment, start with some analytical
thinking.  Many problems associated with consumer electronic equipment
do not require a schematic (though one may be useful).  The majority of
microwave oven problems are easily solved with at most a multimeter (DMM
or VOM).  You do not need an oscilloscope for microwave oven repair unless
you end up trying to fix the logic in the controller - extremely unlikely.

A DMM or VOM is necessary for checking of power supply voltages (NOT
the high voltage, however) and testing of interlock switches, fuses,
wiring, and most of the components of the microwave generator.  This does
not need to be expensive but since you will be depending on its readings,
reliability is important.  Even a relatively inexpensive DMM from Radio
Shack will be fine for most repair work.  You will wonder how you ever
lived without one!  Cost: $25-50.

Other useful pieces of 'test equipment':

* A microwave leakage detector.  Inexpensive types are readily available
  at home centers or by mail order.  These are not super accurate or
  sensitive but are better than nothing.  Also see the sections: "Microwave leakage meters" and "Simple microwave leak detectors".

* A microwave power detector.  These can be purchased or you can make one
  from a small neon (NE2) or incandescent bulb with its lead wires twisted
  together.  Sometimes these homemade solutions do not survive for long
  but will definitely confirm that microwave power is present inside the
  oven chamber.  Note: always have a load inside the oven when testing - a
  cup of water is adequate.

* A thermometer (glass not metal) to monitor water temperature during
  power tests.

* High voltage probe (professional, not homemade!).  However, this is
  only rarely actually required.  Low voltage, resistance, or continuity
  checks will identify most problems.  WARNING: the high voltage in a
  microwave oven is NEGATIVE (-) with respect to the chassis.  Should
  you accidentally use the wrong test probe polarity with your meter,
  don't just interchange the probes = it may be last thing you ever do.
  Unplug the oven, discharge the HV capacitor, and only then change the

There are special magnetron and microwave test instruments but unless you are
in the business, these are unnecessary extravagances.

  4.5) Safe discharging of the high voltage capacitor

It is essential - for your safety and to prevent damage to the device under
test as well as your test equipment - that the large high voltage capacitor
in the microwave generator be fully discharged before touching anything
or making measurements.  While these are supposed to include internal
bleeder resistors, these can fail.  In any case, several minutes may be
required for the voltage to drop to negligible levels.

The technique I recommend is to use a high wattage resistor of about 5 to
50 ohms/V of the working voltage of the capacitor.  This will prevent the
arc-welding associated with screwdriver discharge but will have a short enough
time constant so that the capacitor will drop to a low voltage in at most a
few seconds (dependent of course on the RC time constant and its original

* For the high voltage capacitor in a microwave oven, use a 25 W or larger
  100 K ohm resistor for your discharge widget with a clip lead to the
  chassis.  The reason to use a large (high wattage) resistor is again not
  so much power dissipation as voltage holdoff.  You don't want the HV
  zapping across the terminals terminals of the resistor.

* Clip the ground wire to an unpainted spot on the chassis.  Use the discharge
  probe on each side of the capacitor in turn for a second or two.  Since the
  time constant RC is about .1 second, this should drain the charge quickly and

* Then, confirm with a WELL INSULATED screwdriver across the capacitor
  terminals.  If there is a big spark, you will know that somehow, your
  original attempt was less than entirely successful.  There is a very slight
  chance the capacitor could be damaged by the uncontrolled discharge but at
  least there will be no danger.

* Finally, it is a good idea to put a clip lead across the capacitor terminals
  just to be sure it stays fully discharged while you are working in the area.
  Yes, capacitors have been known to spontaneously regain some charge.  At
  worst, you will blow the fuse upon powering up if you forget to remove it.

WARNING: DO NOT use a DMM for checking voltage on the capacitor unless you
have a proper high voltage probe.  If your discharging did not work, you may
blow everything - including yourself.

A suitable discharge tool can be made as follows:

* Solder one end of the appropriate size resistor (100K ohms, 25W in this case)
  to a well insulated clip lead about 2 to 3 feet long.  Don't just wrap it
  around - this connection must be secure for safety reasons.

* Solder the other end of the resistor to a well insulated contact point
  such as a 2 inch length of bare #14 copper wire mounted on the end of a
  2 foot piece of PVC or Plexiglas rod which will act as an extension handle.

* Secure the resistor to the insulating rod with some plastic electrical tape.

This discharge tool will keep you safely clear of the danger area.  The
capacitor discharge indicator circuit described in the document: "Capacitor
Testing and Safe Discharging" can be built into the discharge tool if desired.

Again, always double check with a reliable high voltage meter or by shorting
with an insulated screwdriver!

Reasons to use a resistor and not a screwdriver to discharge capacitors:

1. It will not destroy screwdrivers and capacitor terminals.

2. It will not damage the capacitor (due to the current pulse).

3. It will reduce your spouse's stress level in not having to hear those
   scary snaps and crackles.

  4.6) Getting inside a microwave oven

You will void the warranty - at least in principle.  There are usually no
warranty seals on a microwave so unless you cause visible damage or mangle the
screws or plastic, it is unlikely that this would be detected.  You need to
decide.  A microwave still under warranty should probably be returned for
warranty service for any covered problems except those with the most obvious
and easy solutions.

Unplug the unit!  Usually, the sheet metal cover over the top and sides
is easily removed after unscrewing 8-16 philips head sheet metal screws.
Most of these are on the back but a few may screw into the sides.  They
are not usually all the same!  At least one of these includes a lockwasher
to securely ground the cover to the case.  Make note of any differences
in screw types so they can be put back in the same place.  The cover will
then lift up and off.  Note how fingers on the cover interlock with
the main cabinet - these are critical to ensure prevention of microwave
leakage after reassembly.

Discharge the high voltage capacitor as described in the section: "Safe discharging of the high voltage capacitor" before even thinking about touching

A schematic showing all of the power generation components is usually
glued to the inside of the cover.  How much of the controller is included
varies but is usually minimal.

Fortunately, all the parts in a microwave can be easily replaced and most of
the parts for the microwave generator are readily available from places
like MCM Electronics, Dalbani, and Premium Parts.

Reassemble in reverse order.  Take particular care to avoid pinching any
wires when reinstalling the cover.  Fortunately, the inside of a microwave
is wide open and this is not difficult.  Make sure ALL of the metal fingers
around the front edge engage properly with the front panel lip.  This is
critical to avoid microwave emissions should the waveguide or magnetron
become physically damaged in any way.  Confirm that the screws you removed
go back in the proper locations, particularly the one that grounds the
cover to the chassis.

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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]