Wiki: Microwave repair

Feedback welcome

NT

Some microwave faults are fairly easy to repair.

=3D=3DSafety=3D=3D Microwaves contain more dangers inside the workings than most household app= liances, and even experienced techs have occasionally been killed working o= n them. As with any DIY task, some competence is required.

If in any doubt about your ability to do such work safely, don't.

Responsibility for safety is entirely yours. This article gives info, but a= nyone can edit it at any time, opinions on safety do vary, and assumptions = get made.

=3D=3D=3DCapacitor discharge=3D=3D=3D The HV capacitor should always be safely discharged before working on a nuk= e. They usually discharge themselves, but when they don't the results have = a habit of being deadly.

Attach a wire from metal case to screwdriver shaft. Prod both capacitor ter= minals at the same time with the screwdriver. Repeat.

=3D=3DBodges=3D=3D Sometimes buying the right parts isn't worth it, but there are other option= s that work. Ones that are safe & usually work are included here.

=3D=3DFault Finding=3D=3D

=3D=3D=3DNo sign of life=3D=3D=3D Usually the main fuse failed due to an interlock fault. This often takes ou= t the interlock resistor. DO NOT replace the fuse until correct operation o= f interlock parts has been verified, and interlock resistor tests good.

Sometimes the interlock fail is caused by door misalignment. Adjust hinges = slightly so it aligns correctly.

Sometimes door realignment is beyond the end user. An easy bodge is to glu= e a bit of a sheet material to the uderside edge of the door so the shim li= fts the door slightly to its correct position as it closes.

=3D=3D=3DBurning spot on roof of cooking cavity=3D=3D=3D The microwave rf energy enters the cooking cavity through a waveguide cover= made of mica or fibreglass. If burnt muck builds up on this it eventually = arcs and burns.

Remove the waveguard cover and check the oven now works properly, heating o= nly water. Don't continue using it without its the cover, or it won't last = long. Cut a new piece to shape and fit.

Occasionally they still arc with the cover removed, due to muck in the mout= h of the waveguide. Remove muck and it should be good - but you need to be = thorough.

=3D=3D=3DUneven heating=3D=3D No nuke is perfect at this, but excessively uneven heating creates a risk o= f food poisoning. Causes are stirrer not turning (when fitted), and turntab= le not turning.

The most even cooking machines have both turntable and stirrer.

=3D=3D=3DTurntable doesn't turn=3D=3D=3D Usually the turntable isn't engaging correctly with the turntable motor spi= ndle, often due to the wrong bits being used. Get the right part that inter= faces the 2, or get the right turntable, or modify a plastic part to get th= em to work with each other.

If the turntable motor doesn't slowly revolve (at 3 or 6 rpm), it can be re= placed with one from almost any other microwave.=20

Access to this motor is via an access flap under the machine. Some covers a= re screwed on, some you have cut out and refit in a different position afte= rwards with screws. Refitting these takes patience.

If you find there's no motor there, you may have a belt drive turntable. So= me old machines geared down the main fan and ran turntable/stirrer by long = rubber bands. For a band of suitable dimensions, look at suppliers for othe= r electronic equipment that uses bands/belts. Stationery rubber bands somet= imes work, and sometimes last years - not recommended, but often workable.

=3D=3D=3DStirrer doesn't turn=3D=3D=3D Generally these are driven by the air current used to cool the magnetron. I= f they won't rotate, the food cooks unevenly. Either the central mounting i= s dirty and sticking, or the air path is amiss, typically due to roof linin= g fixings coming out. The amount of force the air puts on the stirrer is ve= ry slight, sometimes stirrers turn freely by hand, but not quite freely eno= ugh to turn in the airflow.

Remove roof lining, clean stirrer mounting thoroughly, refit lining. Don't = oil the central mounting, it'll only clog with dirt.

Some old machines geared down the main fan to run the turntable/stirrer by = long rubber bands.

=3D=3D=3DFails to cook=3D=3D=3D Everything looks like it works, but it fails to heat food. A fault with any= of the following will do this:

  • control system
  • transformer
  • diode
  • capacitor
  • magnetron

All the above are frequent offenders, so the only option is to follow the c= ircuit through to see where its failing. This means testing live mains and = high voltage circuits, which is inherently dangerous if you lack the skill = set.

If you can't fault find, but have a scrap donor machine and are willing to = try something, the HV diode is a frequent failer, easy to replace, and in m= ost cases one from a random nuke will do. It must be fitted the right way r= ound, or the oven won't cook. HV capacitors are often also easily swappable= , a random swap often works but no guarantees.

=3D=3D=3DFire=3D=3D=3D Microwave food fires look bad, but if the door is ok and the outside of the= machine's ok, repair is generally straightforward. Clean the cooking cavit= y out thoroughly and the machine usually works fine again.

Often its necessary to replace a fried waveguide cover or roof lining. You = can test it first without these. If the cover's reusable it needs a very th= orough clean, or will fail.

=3D=3D=3DElectronic control faults=3D=3D=3D Seldom worth repairing. Mechanical controls (rotary knobs) are a fair bit m= ore reliable.

=3D=3D=3DMechanical control faults=3D=3D=3D These don't often fail. Burnt switch contacts can prevent cooking. Clean th= e switch contact surfaces with very fine sandpaper, once they're clean they= 're good. Other faults are generally very visible when the machine's powere= d up.

=3D=3D=3DNoise=3D=3D=3D The 2 usual causes of noise are

*Side of metal case affected by transformer's magnetic field **put padding between the 2 to stop it resonating. **putting a small wad of folded paper between microwave side and the cabine= t its next to also does the trick, as long as you dont block any holes.

*Fan blades fouling housing

** adjust housing position slightly to clear the blades ** or slacken fan motor fixing screws and move it very slighly ** if all else fails, file the blade tips slightly on all blades equally. S= andpaper works.

=3D=3D=3DBulb failure=3D=3D=3D Some machines have a small unscrewable plate in the side to reach the bulb.= With some you need to remove the whole outer cover - beware this can expos= e lethal high voltages (far above mains voltage).

Most microwaves take standard small bulbs designed for microwaves.

  • I've often used small regular SES lamps instead, they just have shorter a= verage life in a microwave.

Combination nukes use oven rated SES bulbs

  • again one can substitude ordinary ones, but there's a slight risk of the = bulb base coming away, making replacement difficult later, so its not recom= mended.

A minority of microwaves take less common bulb types. typically the bulb is= screwed o the chassis and uses push-on crimp terminals. Either get the rig= ht bulb from a repair shop, parts dealer or another nuke, or replace the bu= lbholder with a standard SES type.

Least common of all are machines that run 2x 110v bulbs in series. Either g= et the right type, or make life easier by replacing one with an SES holder = & 240v bulb, and shorting the other one out.

If replacing a lightbulb with a non-original type, its good practice to mar= k the recommended wattage by the holder. 25w is most common.

=3D=3D=3DLight too dim=3D=3D=3D A common issue, making it hard to see when the food's hot.

  • First clean both sides of the clear plastic or glass the light comes thro= ugh, and clean the door.

Fixes that void any warranty include:

  • increase bulb wattage
  • fit white card behind the bulb to reflect light into the cooking cavity
  • In both cases, first check the bulb is surrounded by metalwork rather tha= n plastic; these approaches are best avoided if its surrounded by plastic.

If replacing a lightbulb with a non-original type, its best to mark the rec= ommended wattage by the holder.

=3D=3D=3DMachine stops cooking after 15 minutes=3D=3D=3D Domestic microwaves are designed to cook for only about 15 minutes on full = power. Longer times are workable at lower power settings. The limitation is= transformer temperature, to cook longer would take a much larger transform= er.

Machines that run the fan when the door's open cool the transformer faster.

=3D=3D=3DCanning spoilage=3D=3D=3D Microwaves are not suitable for canning. The heat isn't even enough, and do= mestic microwaves can't apply power continuously.

=3D=3DRepairs=3D=3D

=3D=3D=3DTransformer=3D=3D=3D

These should be replaced with spares designed to fit the oven. But the cost= isn't worthwhile in most cases.

The author has before transplanted unknown transformers from scrap ovens (i= t was once worth doing) with successes, using ovens with the same rated pow= er input (ignore power output claims). Obviously all bets are off when doin= g this.

=3D=3D=3DMagnetron=3D=3D=3D An understanding of the behaviour of microwave rf is advisable if replacing= magnetrons. Key safety issues are anything but obvious if you don't have s= uch knowledge.

Don't fit megnetrons not designed for the model of oven. Unlike transformer= s, slight differences in physical layout can cause microwave leakage & fail= ures.

=3D=3D=3DDiode=3D=3D=3D

The HV diode is usually plugged onto the HV capacitor, and easily replaced.= It must be connected the right way round, or the oven won't cook.

=3D=3D=3DCapacitor=3D=3D=3D

Either use a part intended for the model, or another that's the right capac= ity, at least as high rated voltage, and physically fits.

=3D=3D=3DWaveguide cover=3D=3D=3D

Its sold in sheets, and you cut it to fit.

=3D=3D=3DFuse=3D=3D=3D

With most electrical goods, the fuse is a safety element reducing risk of f= ire & shock. In a microwave oven the fuse performs an important extra role.= Its a key part of the safety interlock system preventing users being micro= waved. When an interlock error occurs the fuse must blow to prevent the use= r opening the oven door with the microwave source being on. This means usin= g the correct rating and breaking capacity of the fuse is important.

When the fuse blows in a microwave, it often means there has been an interl= ock error. Such an occurrence often burns out the interlock resistor or som= etimes an interlock switch is faulty. When this occurs, replacing the fuse = will make the oven work again, but it won't be properly safe. The next time= an interlock error occurs the fuse won't blow, and you may expose your arm= or head to intense microwave radiation.

If a fuse blows, test the interlock resistor and interlock switches before = replacing it.

=3D=3D=3DThermal cutout=3D=3D=3D Bimetal thermostats cut power when transformer or magnetron overheat. These= low cost parts can be had from many electronic component suppliers.

Replace with one with the same temp rating - each one in a machine has a di= fferent temp rating.

If for some reason you use a different temperature one, pick one with a bit= lower temp rating. A lower temp rating reduces how long the oven can cook = on full power. Fitting a higher temp cutout is likely to cause a major fail= ure.

=3D=3DFault prevention=3D=3D

*Keep the waveguide cover clean.

*Don't get hammered and put the noodles on for 30 minutes. Its not clever.

=3D=3DParts=3D=3D New parts can be had from the usual sources, but are often an unnecessary s= pend, as free used parts are widely available from dead machines.

Scrap nukes provide fuses, bulbs, diodes, capacitors, motors, interlock res= istors, and sometimes reusable waveguide covers. Other parts aren't usually= worth reusing. The odds of a random turntable fitting a given nuke are fai= rly low.

=3D=3DRecycling=3D=3D

*door glass makes a chopping board *turntable motor makes a megger *transformers can be used to make welders, but little else

=3D=3DSee Also=3D=3D

[[Category:Appliances]] [[Category:Fault Finding]] [[Category:Repair]]
Reply to
meow2222
Loading thread data ...

s/nuke/microwave/g B-)

Some times you use microwave at others nuke.

Nuke is slang and my use of the term in relation to microwave ovens is a verb not a noun ie "one nukes ones pot noodle in the nuker".

Reply to
Dave Liquorice

First, let me say that I am glad not to be the only one to have found the two 110 lamps in series bodge, I think it was a little Sanyo microwave.

Safety. I think the best advice for discharging the capacitor is to use two screwdrivers with well insulated plastic handles. Wires with or without crocodile clips seem unnecessary, and give more potential for getting your heart in the circuit.

In the year or so that I was repairing microwave ovens as my day job, I never once felt the need to take voltage measurements from the secondary side of the transformer or beyond. Frankly the circuit is so simple, only 4 components, cold testing on the resistance range will find most faults. I don't think we should encourage live testing of the HT, and here speaks someone who was a TV engineer throughout the

70s and 80s so I am no wimp!

Usual failure modes need discussing These are in the order of likelihood in my own experience, with the most likely first. The HT diode goes short or leaky The HT capacitor goes short The magnetron goes short anode to cathode or overheats and cracks one or both magnets (can be seen with a cartful visual inspection).

All the faults above can exist without blowing the mains fuse because the transformer is driven close to saturation normally, so a short on the secondary doesn't have a great impact on the primary. There is sometimes a big 500mA fuse in the transformer secondary enclosed in an insulated housing.

Theory. The basic principles need explaining, the fact that the HT is negative wrt chassis and the diode, capacitor and magnetron form a voltage doubler. The anode of the magnetron is its earthed body.

I think the Wiki has too much of a retro feel from 20 years+ ago when domestic microwaves were built like tanks with a substantial waveguide to plumb the rays into the roof of the cavity with a turbo fan to keep everything cool and enough energy left to work the stirrer turbine in the roof. Perhaps these legacy details could have their own section.

Reply to
Graham.

I always thought that giving capacitors a dead short was generally deprecated, that use of a resistor was better to limit the current

Reply to
newshound

Shorting it is just a precaution in case the internal bleed resistor hasn't done the job for you. In practice you only get a small spark if that.

You can't be too careful.

formatting link

Reply to
Graham.

Not so much fun, though

Reply to
geoff

I've seen it in Sharp nukes. 2 bulbs does give much better lighting, and making them 110v makes them slightly more robust. A pain for the lay user though.

I'm not sure what it would gain people in practical terms. Maybe another article can get into that in more depth, I really think 99% of readers won't be able to use the info.

added section on magnetron covers

If there are other ways to run the stirrer than air & rubber band I can't remember. What else have you found?

NT

Reply to
meow2222

Mark 2 version...

NT

[[image:Microwave Error 2681-9.jpg|right|300px]]

Some microwave faults are fairly easy to repair.

=3D=3DSafety=3D=3D Microwaves contain more dangers inside the workings than most household [[a= ppliance]]s, and even experienced techs have occasionally been killed worki= ng on them. As with any DIY task, some competence is required.

If in any doubt about your ability to do such work safely, don't.

Responsibility for [[safety]] is entirely yours. This article gives info, b= ut anyone can edit it at any time, opinions on safety do vary, and in real = life assumptions get made.

=3D=3D=3DCapacitor discharge=3D=3D=3D The HV capacitor should always be safely discharged before working on a nuk= e. They're normally designed to discharge themselves, but when they fail to= the results are liable to be deadly.

Attach a [[Flex|wire]] from the [[metal]] case to a [[screwdriver]] shaft (= one with an insulating plastic head!). Check its connected to the case and = prod both capacitor terminals at the same time with the screwdriver. Repeat= .

Another way to do it is with 2 insulated screwdrivers and no wire.

=3D=3D=3DLive working=3D=3D=3D We can't recommend it. A mains shock has only a slight risk of death, but o= ver a thousand volts at high current in a microwave is a very different sto= ry.=20

=3D=3DBodges=3D=3D Sometimes buying the right parts isn't worth it, but there are other option= s that work. Ones that are safe & usually work are mentioned here.

=3D=3DFault Finding=3D=3D

=3D=3D=3DNo sign of life=3D=3D=3D Usually the main [[fuse]] failed, often due to an interlock fault. This oft= en takes out the interlock resistor. Don't replace the fuse until correct o= peration of interlock parts has been verified, and the interlock resistor t= ests good.

Sometimes the interlock fail is caused by door misalignment. Adjust hinges = slightly so it aligns correctly.

Sometimes door realignment is beyond the end user. An easy bodge is to glue= a bit of a [[sheet material]] to the uderside edge of the door so the shim= lifts the door slightly to its correct position as it closes.

=3D=3D=3DBurning waveguide cover or magnetron cover=3D=3D=3D Nukes either have a metal waveguide to conduct the microwaves into the cook= ing cavity, with a waveguide cover, or the magnetron is positioned right ne= xt to the cooking cavity with no guide, and a moulded plastic magnetron cov= er.

=3D=3D=3DBurning waveguide cover=3D=3D=3D In waveguide equipped ovens the microwave rf energy enters the cooking cavi= ty through a waveguide cover made of mica or fibreglass. The cover is on th= e roof or high up on the side of the cooking cavity. If burnt [[Cleaning|mu= ck]] builds up on this it eventually arcs and burns.

Remove the burnt waveguide cover and check the oven now works properly, hea= ting only [[water]]. Don't continue using it without its cover, or it won't= last long. Cut a new piece to shape and fit.=20

Use waveguide cover material, not random plastic. The wrong stuff is likely= to catch fire, and deposit muck in the waveguide, which is very difficult = to clean out - and with muck in there, the oven simply shorts out.

Occasionally the oven still arcs with the waveguide cover removed, due to [= [muck]] in the mouth of the waveguide. Remove muck and it should be good - = but you need to be thorough.

=3D=3D=3DBurning magnetron cover=3D=3D=3D The problem is much the same as a burning waveguide cover.=20

If you catch it soon enough, with little damage done, clean the plastic cov= er thoroughly, cut out any carbonisation and refit.

If the cover is beyond repair, it can be replaced with a new one that fits = the model.=20

A bodge option is to just not refit a cover. Any muck that lands on the red= hot magnetron is instantly burnt off, but muck can over many years build u= p around it and eventually short the microwave output or burn. This situati= on is a real pain to sort out, access is very difficult.

=3D=3D=3DUneven heating=3D=3D=3D No nuke is perfect at this, but excessively uneven heating creates a risk o= f food poisoning. Causes are turntable not turning, and (when fitted) stirr= er not turning.

The most even cooking machines have both turntable and stirrer.

=3D=3D=3DTurntable doesn't turn=3D=3D=3D [[image:Turntable motor from nuke 5671-3.jpg|right|200px|Turntable motor]]

Usually the turntable isn't engaging correctly with the turntable [[motor]]= spindle, often due to the wrong bits being used. Get the right part that i= nterfaces the 2, or get the right turntable, or modify a [[plastic]] part t= o get them to work with each other.

If the turntable motor doesn't slowly revolve (at 3 or 6 rpm), it can be re= placed with one from almost any other microwave.

Access to this motor is via an access flap under the machine. Some covers a= re screwed on, some you have to cut out and refit in a different position a= fterwards with [[screws]]. Refitting these takes patience.

If you find there's no [[motor]] there, you might have a belt drive turntab= le. Some old machines geared down the main fan and ran turntable/stirrer by= long rubber bands. For a band of suitable dimensions, look at suppliers fo= r other electronic equipment that uses bands/belts. Stationery rubber bands= often work, and some last years - no promises though.

Occasionally nukes let the user switch off the turntable to allow maximum u= se of the cooking space. These machines always have a stirrer. Even less co= mmon are machines that come with a temperature probe, when its plugged in t= he turntable is stopped. These features are fairly unusual, but its probabl= y worth checking power is reaching the [[motor]].

=3D=3D=3DStirrer doesn't turn=3D=3D=3D Generally these are driven by the air current used to cool the magnetron. I= f they don't rotate, the food cooks unevenly. Either the central mounting i= s [[dirt]]y and sticking, or the air path is amiss, typically due to [[roof= ]] lining fixings coming out. The amount of force the air puts on the stirr= er is slight, sometimes stirrers turn freely by hand, but not quite freely = enough to turn in the airflow.

Remove roof lining, clean stirrer mounting thoroughly, refit lining. Don't = [[oil]] the central mounting, it'll only clog with [[dirt]].

Some old machines geared down the main fan to run the turntable/stirrer by = long rubber bands.

=3D=3D=3DFails to cook=3D=3D=3D Everything looks like it works, but it fails to heat food. A fault with any= of the following will do this:

  • control system
  • transformer
  • diode
  • capacitor
  • magnetron

All the above are frequent offenders, and the easiest way to find the probl= em is test each component on the resistance range with a [[multimeter]]. Th= e problem is usually a shorted or leaky component, or an open HV fuse.

If you can't fault find, but have a scrap donor machine and are willing to = try something,

  • the HV diode is the most frequent failer, easy to replace, and in most ca= ses one from a random nuke will do. It must be fitted the right way round, = or the oven won't cook.
  • HV capacitors are also a common fail, often easily swappable, and a rando= m swap often works but no guarantees.
  • HV fuses also often fail

=3D=3D=3DFire=3D=3D=3D Microwave food [[fire]]s look bad, but if the door is ok and the outside of= the machine's ok, [[repair]] is generally straightforward. [[Clean]] the c= ooking cavity out thoroughly and the machine usually works fine again.

Often its necessary to replace a fried waveguide cover or [[roof]] lining. = You can test it first without these. If the cover's reusable it needs a ver= y thorough clean, or will fail.

=3D=3D=3DElectronic control faults=3D=3D=3D Seldom worth repairing. Mechanical controls (rotary knobs) are a fair bit m= ore reliable.

=3D=3D=3DMechanical control faults=3D=3D=3D [[image:Microwave mechanical controls 5915-3.jpg|right|100px]]

These don't often fail. Burnt switch contacts can prevent cooking. Clean th= e switch contact surfaces with extra fine sandpaper, once they're clean the= y're good. Other faults are generally very visible when the machine's power= ed up.

=3D=3D=3DNoise=3D=3D=3D The 2 usual causes of excessive noise are

*Side of [[metal]] case affected by transformer's magnetic field **put padding between the 2 to stop it resonating. **putting a small wad of folded paper between microwave side and the cabine= t its next to also does the trick, as long as you don't block any holes.

*Fan blades fouling housing

** adjust housing position slightly to clear the blades ** or slacken fan motor fixing screws and move it very slighly ** if all else fails, file the blade tips slightly on all blades equally. S= andpaper works.

=3D=3D=3DBulb failure=3D=3D=3D [[image:Appliance lamp 4218-2.jpg|right|120px]]

Some machines have a small unscrewable plate in the side to reach the [[bul= b]]. With some you need to remove the whole outer cover - this can expose l= ethal high voltages (far above mains voltage).

Most microwaves take standard small bulbs designed for microwaves.

  • I've often used small regular SES lamps instead, they just have shorter a= verage life in a microwave.

Combination nukes use oven rated SES bulbs

  • again one can substitude ordinary ones, but there's a slight risk of the = bulb base coming away, making replacement difficult later, so its not best = practice.

A minority of microwaves take less common [[bulb]] types. typically the bul= b is [[screw]]ed to the chassis and connected with push-on crimp terminals.= Either get the right bulb from a repair shop, parts dealer or another nuke= , or replace the bulbholder with a standard SES type.

Least common of all are machines that run 2x 110v bulbs in series. Either g= et the right type, or make life easier by replacing one with an SES holder = & 240v bulb, and shorting the other one out.

If replacing a lightbulb with a non-original type, its good practice to mar= k the recommended wattage by the holder. 25w is most common.

Finally, if you never want a bulb to fail again you can convert the oven to= use a mains LED bulb. Because it'll get hot in use at times, the LED needs= to be derated by fitting a series capacitor to cut its light output to aro= und half. If this is ignored, its likely to not last. LEDs aren't usable in= combination cookers, they can't take that much heat.

=3D=3D=3DLight too dim=3D=3D=3D A common issue, making it hard to see when the food's hot or boiling over.

  • First clean both sides of the clear plastic or glass the light comes thro= ugh, and clean the door.

Fixes that void any warranty include:

  • increase bulb wattage a bit
  • fit white card behind the bulb to reflect light into the cooking cavity
  • In both cases, first check the bulb is surrounded by metalwork rather tha= n plastic; these approaches are best avoided if its surrounded by plastic.

If replacing a lightbulb with a non-original type, its best to mark the rec= ommended wattage by the holder.

=3D=3D=3DMachine stops cooking after 15 minutes=3D=3D=3D Domestic microwaves are designed to cook for about 15 minutes on full power= at most. Longer times are workable at lower power settings. The limitation= is transformer temperature, to cook longer would take a much larger transf= ormer.

Machines that run the fan when the door's open cool the transformer faster.

=3D=3D=3DCanning spoilage=3D=3D=3D Microwaves aren't suitable for canning. The heat isn't even enough, and dom= estic microwaves can't apply power continuously for long enough (but they p= retend to).

=3D=3D=3DOven keeps cooking with the door part open=3D=3D=3D I have seen an old oven still in use that continued cooking until the door = was part way open. Unless you want to expose the inside of your head to hal= f a kilowatt of cooking power, cut the mains lead off and scrap it, or dona= te it to a museum. Such ovens can't be made safe, adjusting the interlock c= orrectly still leaves them dangerous.

=3D=3D=3DRust=3D=3D=3D Rust in the cooking cavity is harmless as long as there's still sound metal= under it. If the rust patch shows any sign of coming apart when jabbed, it= s time to scrap the oven. (Welding is possible, but seldom worth it.) Rust = patches can be made good with car rust remover & paint. Oiling the rust is = a simple way to stop it spreading.

=3D=3DRepairs=3D=3D

=3D=3D=3DTransformer=3D=3D=3D

These should be replaced with spares designed to fit the oven. But the cost= isn't worthwhile in most cases.

The author has before transplanted unknown transformers from scrap ovens (i= t was once worth doing) with successes, using ovens with the same rated pow= er input (ignore power output claims). Obviously all bets are off when doin= g this.

=3D=3D=3DMagnetron=3D=3D=3D An understanding of the behaviour of microwave rf is advisable if replacing= magnetrons. Key safety issues are anything but obvious if you don't have s= uch knowledge.

Don't fit megnetrons not designed for the model of oven. Unlike transformer= s, slight differences in physical layout can cause microwave leakage & oven= failure.

=3D=3D=3DDiode=3D=3D=3D

0819-4 Microwave HV diodes & resistor.bmp

The HV diode is usually plugged onto the HV capacitor, and easily replaced.= It must be connected the right way round, or the oven won't cook.

=3D=3D=3DCapacitor=3D=3D=3D

Either use a part intended for the model, or another that's the right capac= ity, at least as high rated voltage, and physically fits.

=3D=3D=3DWaveguide cover=3D=3D=3D

The material's sold in sheets, cut it to fit. Mica sheets are fragile, don'= t bend them.

=3D=3D=3DMagnetron cover=3D=3D=3D

=3D=3D=3DMains fuse=3D=3D=3D

With most electrical goods, the [[fuse]] is a safety element reducing risk = of [[fire]] & shock. In a microwave oven the fuse performs an important ext= ra role. Its a key part of the safety interlock system preventing users bei= ng microwaved. When an interlock error occurs the fuse must blow to prevent= the user opening the [[oven]] door with the microwave source being on. Thi= s means using the correct rating and breaking capacity of the fuse is impor= tant.

When the fuse blows in a microwave, it often means there has been an interl= ock error. Such an occurrence often burns out the interlock resistor or som= etimes an interlock switch is faulty. When this occurs, replacing the fuse = will make the oven work again, but it won't really be safe. The next time a= n interlock error occurs the fuse won't blow, and you may expose your arm o= r head to intense microwave radiation.

If a fuse blows, test the interlock resistor and interlock switches before = replacing it.

=3D=3D=3DHV fuse=3D=3D=3D Some ovens have a high voltage 500mA fuse on the output of the main transfo= rmer to reduce fire risk. This can go open circuit. Don't use a mains volta= ge fuse to repalce it. Its normally housed in a short plastic tube moulded = in 2 halves and snapped together.

=3D=3D=3DThermal cutout=3D=3D=3D [[image:Bimetal thermal 4909-2.jpg|right|100px|Thermal cutout]]

Bimetal thermal cutouts cut power when transformer or magnetron overheat. T= hese low cost parts can be had from many electronic component suppliers.

Replace with one with the same temp rating - each one in a machine has a di= fferent temp rating.

If for some reason you use a different temperature one, pick one with a bit= lower temp rating. A lower temp rating reduces how long the oven can cook = on full power. Fitting a higher temp cutout is likely to cause a major fail= ure, microwave transformers are pushed pretty hard already.

=3D=3DParts=3D=3D New parts can be had from the usual sources, but are often an unnecessary s= pend, as free used parts are widely available from dead machines.

Scrap nukes provide [[fuse]]s, [[bulb]]s, diodes, capacitors, [[motor]]s, i= nterlock resistors, and sometimes reusable waveguide covers. Other parts ar= en't usually worth reusing. The odds of a random turntable fitting a given = nuke are fairly low.

=3D=3DFault prevention=3D=3D

*Keep the waveguide cover or magnetron cover clean.

*Don't get [[hammer]]ed and put the noodles on for 30 minutes. Its not clev= er.

=3D=3DRecycling=3D=3D

*door [[glass]] makes a chopping board *turntable motor makes a [[megger]] *transformers can be used to make welders, but little else

=3D=3DSee Also=3D=3D

[[Category:Appliances]] [[Category:Fault Finding]] [[Category:Repair]]
Reply to
meow2222

b. With some you need to remove the whole outer cover - beware this can exp= ose lethal high voltages (far above mains voltage).

average life in a microwave.

e bulb base coming away, making replacement difficult later, so its not rec= ommended.

is screwed o the chassis and uses push-on crimp terminals. Either get the r= ight bulb from a repair shop, parts dealer or another nuke, or replace the = bulbholder with a standard SES type.

get the right type, or make life easier by replacing one with an SES holde= r & 240v bulb, and shorting the other one out.

ark the recommended wattage by the holder. 25w is most common.

The bulb on our microwave failed. After much swearing I managed to get the cover off.The bulbs on our microwave are SOLDERED in place. Cue exponential swearing and even more swearing trying to get the darned cover to fit back on.

-- Halmyre

Reply to
Halmyre

"Notes on the Troubleshooting and Repair of Microwave Ovens"

formatting link
Sci.Electronics.Repair

Reply to
Phil Addison

We used to have a Thorn with a temperature probe, and the turntable still turned with it in use. The probe was connected through slip-rings or something that allowed it to rotate with the food. It was a boon as you could set it to cook to a certain temperature, but sadly the probe failed after a couple of year.

Phil

Reply to
Phil Addison

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.