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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]]