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MCO160uw triping breaker I replaced primary switch question now is how to test other switches and circuit now blown the fuse on the main power board

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  • Roy Bratt
    Roy Bratt Apr 01, 2015

    tripping when door is opened seems that got clipped off my question

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6 Suggested Answers

6ya6ya
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Posted on Jan 02, 2017

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MicrowaveSvc
  • 9047 Answers

SOURCE: No power

The door switches are designed to prevent the unit from running while the door is open. You probably have a blown fuse, and it's a white or dark grey ceramic fuse of 15A or 20A, available from local big box stores or appliance parts stores. The fuse is usually located on the floor of the chassis behind the control panel, or mounted in the same area as the door switches. Also, I'm really curious how the door switch got stuck while cleaning? That sounds scary...

Posted on Nov 13, 2006

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MicrowaveSvc
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SOURCE: GE Spacemaker Microwave Blown Fuse replaced still no power

If you measure across the varistor leads with it still in the circuit, you should measure around 100-300 ohms, which is the DC resistance of the primary of the low voltage transformer.

If you read infinity / open the primary of the low voltage transformer is bad.

If the varistor is bad, it will be shorted and usually it will be cracked or split. This is a much simpler way to test the varistor.

Have you checked the magnetron thermal cutout (TCO) (or thermostat if so equipped) and the oven TCO? These are the leading causes of a dead GE when the fuse is okay.

You didn't mention the model number. What is it?

Please reply back here if you still need help.

We're happy to help you. Once we have all your information and offer a final solution, we'd appreciate your thoughtful rating of our answer.

Posted on Jul 18, 2008

MicrowaveSvc
  • 9047 Answers

SOURCE: Replacing the fuse of a MCO160UW

A microwave can be dead for many reasons.

It may be the fuse, which is usually located on the floor of the oven behind the control panel or between the door switches.

If the fuse is good, it may be an open thermostat or thermal cutout (TCO) / thermal fuse on or near the magnetron or on top of the cavity / body of the oven.

If it goes dead for a while during or after cooking then comes back on, the magnetron is probably overheating and causing the magnetron thermostat to open.

Then when it cools, it closes the circuit and allows power through again.

When checking thermostats, if it has a hood fan thermostat, that should read open, as opposed to the others, which should read closed.

If it went dead almost immediately after pressing the Start pad, that's usually a shorted high-voltage capacitor.

If it went dead a few seconds after pressing the Start pad, that's usually a failing high-voltage transformer.

If it goes dead or blows the breaker (or GFI) when you plug it in or open or close the door, then there's a problem with a door switch or door switch mount.

If it's intermittent or random, it may be a bad connection, usually on the control board or a loose fuse holder, or even an intermittent fuse.

You should do a continuity test on the fuse while it's in the holder (with the microwave unplugged, of course) then turn the fuse by hand or take it out and put it back in, then test it again.

If you remove the fuse, then press the meter leads against the ends, it can allow internal contact to be made and make a bad fuse appear to be good.

If you or someone you know decide to look into it, we have critical safety information and disassembly information at our site, and our link is at our listing here on FixYa.

There may also be a "mini-manual" hidden inside the unit behind the control panel or hidden on the left side behind the grille, which is very helpful when troubleshooting & testing.

We're happy to help you and we'd appreciate your thoughtful rating of our answer.

Posted on Jul 19, 2008

MicrowaveSvc
  • 9047 Answers

SOURCE: Microwave Panasonic Genius Prestige Model

A microwave can be dead for many reasons.

It may be the fuse, which is usually located behind the grille or on the floor of the oven behind the control panel or between the door switches.

If the fuse is good, it may be an open thermostat or thermal cutout (TCO) / thermal fuse on or near the magnetron or on top of the cavity / body of the oven.

If it goes dead for a while during or after cooking then comes back on, the magnetron is probably overheating and causing the magnetron thermostat to open.

Then when it cools, it closes the circuit and allows power through again.

When checking TCOs or thermostats, if it has a hood fan thermostat, that should read open, as opposed to the others, which should read closed.

The TCOs you need to be concerned usually with have all black or white wires only. Please reply with photos of your interior if you have questions.

If it went dead almost immediately after pressing the Start pad, that's usually a shorted high-voltage capacitor.

If it went dead a few seconds after pressing the Start pad, that's usually a failing high-voltage transformer.

If it goes dead or blows the breaker (or GFI) when you plug it in or open or close the door, then there's a problem with a door switch or door switch mount.

If it's intermittent or random, it may be a bad connection, usually on the control board or a loose fuse holder, or even an intermittent fuse.

You should do a continuity test on the fuse while it's in the holder (with the microwave unplugged, of course) then turn the fuse by hand or take it out and put it back in, then test it again.

If you remove the fuse, then press the meter leads against the ends, it can allow internal contact to be made and make a bad fuse appear to be good.

If you or someone you know decide to look into it, we have critical safety information and disassembly information at our site, and our link is at our listing here on FixYa.

You can order Panasonic parts here.

You can find an authorized Panasonic servicer here.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

Posted on Sep 28, 2008

Treefrog15
  • 127 Answers

SOURCE: How do you reset the microwave power? Is there an

There is an internal cartridge fuse, as well as thermal fuses. It is not recommended that you attempt any internal repairs on a microwave due to the presence of very high voltages and the danger of microwave radiation if not reassembled correctly. Residential microwaves, if not under warrranty, are generally considered disposable. Parts and service are very expensive.

Posted on Feb 25, 2010

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2 Answers

Microwave will not work No Power, No clock nothing works


Remove the outer panel and check the fuse which is usually mounted near the power cord inlet.

Oct 19, 2016 | Microwave Ovens

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Continued


What can go wrong The most common problems occur in the microwave generating portion of the system, though the controller can be blown by a lightning strike or other power surge. Bad interlock switches probably account for the majority of microwave oven problems. Also, since the touchpad is exposed, there is a chance that it can get wet or damaged. If wet, a week or so of non-use may cure keys that don't work. If damaged, it will probably need to be replaced - this is straightforward if the part can be obtained, usually direct from the manufacturer. Unfortunately, it is an expensive part ($20-50 typical). The interlock switches, being electromechanical can fail to complete the primary circuit on an oven which appears to operate normally with no blown fuses but no heat as well. Faulty interlocks or a misaligned door may result in the fuse blowing as described above due to the incorrect sequencing of the door interlock switches. Failed interlocks are considered to be the most common problems with microwave ovens, perhaps as high as 75% of all failures
No adjustments should ever be required for a microwave oven and there are no screws to turn so don't look for any!

General system problems The following problems are likely power or controller related and not in the microwave generator unless due to a blown fuse or bad/intermittent connections:
  • Totally dead oven.
  • No response to any buttons on touchpad
  • Oven runs when door is still open.
  • Oven starts on its own as soon as door is closed.
  • Oven works but display is blank.
  • Whacked out controller or incorrect operation.
  • Erratic behavior.
  • Some keys on the touchpad do not function or perform the wrong action.
  • Microwave oven does not respond to START button.
First, unplug the microwave oven for a couple of minutes. Sometimes, the microcontroller will get into a whacko mode for some unknown reason - perhaps a power surge - and simply needs to be reset. The problem may never reoccur.
Note: when working on controller related problems, unplug the connection to the microwave generator (HV transformer primary) from the power relay or triac - it is often a separate connector. This will prevent any possible accidental generation of microwave energy as well as eliminating the high voltage (but not the AC line) shock hazard during servicing.
If this does not help, there is likely a problem with the controller circuitry or its power and you will have to get inside the oven.


Uninvited guests Some cockroaches (or other lower life forms) may have taken up residence on the controller circuit board. It is warm, cozy, safe, and from their point of view makes an ideal habitat. If you got the microwave oven from a flea market, garage sale, the curb, a relative, or friend, or if your kitchen isn't the cleanest in the world, such visitors are quite possible. Creatures with six or more legs (well, some two legged varieties as well) are not known for their skills in the areas of housekeeping and personal hygiene. Clean the circuit board and connectors thoroughly with water and then isopropyl alcohol. Dry completely. Inspect the circuit traces for corrosion or other damage. If there are any actual breaks, these will have be be jumpered with fine wire and then soldered. Hopefully, no electronic components were affected though there is always a slight possibility of other problems.
Totally dead oven First, check power to the outlet using a lamp or radio you know works. The fuse or circuit breaker at your service panel may have blown/tripped due to an overload or fault in the microwave oven or some other appliance. You may just have too many appliances plugged into this circuit - microwave ovens are high current appliances and should be on a dedicated circuit if possible. If you attempt to run a heating appliance like a toaster or fryer at the same time, you *will* blow the fuse or trip the circuit breaker. A refrigerator should never be plugged into the same circuit for this reason as well - you really don't want it to be without power because of your popcorn! If you find the fuse blown or circuit breaker tripped, unplug everything from the circuit to which the microwave is connected (keep in mind that other outlets may be fed from the same circuit). Replace the fuse or reset the circuit breaker. If the same thing happens again, you have a problem with the outlet or other wiring on the same branch circuit. If plugging in the microwave causes the fuse to blow or circuit breaker to trip immediately, there is a short circuit in the power cord or elsewhere.
The microwave oven may be powered from a GFCI outlet or downstream of one and the GFCI may have tripped. (Removing a broken oven lamp has been known to happen.) The GFCI outlet may not be in an obvious location but first check the countertop outlets. The tripped GFCI could be in the garage or almost anywhere else! Pushing the RESET button may be all that's needed.
Next, try to set the clock. With some ovens the screen will be totally blank following a power outage - there may be nothing wrong with it. Furthermore, some ovens will not allow you perform any cooking related actions until the clock is set to a valid time.
Assuming these are not your problems, a fuse has probably blown although a dead controller is a possibility.
If the main fuse is upstream of the controller, then any short circuit in the microwave generator will also disable the controller and display. If this is the case, then putting in a new fuse will enable the touchpad/display to function but may blow again as soon as a cook cycle is initiated if there is an actual fault in the microwave circuits.
Therefore, try a new fuse. If this blows immediately, there may be a short very near the line cord, in the controller, or a defective triac (if your oven uses a triac). Or, even a shorted oven lamp - remove and inspect the light bulb and socket.
If it does not blow, initiate a cook cycle (with a cup of water inside). If the oven now works, the fuse may simply have been tired of living. This is common.
If the fuse still blows immediately, confirm that the controller is operational by unplugging the microwave generator, power relay, and/or triac from the controller. If a new fuse does not now blow when a cook cycle is initiated - and it appears to operate normally - then one of the components in the microwave generator is defective (shorted).
Some models have a thermal fuse as well and this may have failed for no reason or a cooling fan may not be working and the oven overheated (in which case it probably would have died while you were cooking something for an important guest - assuming you would use a microwave oven for such a thing!).
Other possible causes: bad controller power supply or bad controller chip.


Totally dead oven after repair On some microwave ovens, there is at least one cabinet screw that is slightly longer than all the others. This engages a safety interlock which prevents the oven from receiving power if the correct screw is missing or in the wrong hole. Check the length of all the screws and locate the interlock switch behind one of the screw holes. I don't know how common this practice is but have heard of it on some Sharp models.

Dead controller The most common way that the controller circuitry can be harmed is by a power surge such as from a lightning strike. Hopefully, only components on the primary side of the power transformer will be affected.
  • Check the primary of the power transformer - if it is open, there may be a fuse/thermal fuse underits outer insulation. If not, the transformer will need to be replaced. There is a good chance that the surge didn't propagate beyond the transformer and thus the rest of the controlled should be unaffected.
  • In some cases, circuit board traces may have been vaporized (but repair may still be possible by simply jumpering across the crater). Some of these thin traces may be there specifically to act as fuses - and there may even be spares to use for just this situation!
  • Assuming that the main fuse and power transformer primary checks out, then check the power supply for the controller next.
  • As always, also check for bad solder connections.
If the controller power supply is working and there is still no sign of life (dead display and no response to buttons) the microcontroller chip or some other part may be bad. It could be a simple part like a capacitor or diode, but they would all need to be tested. At this point, a schematic of the controller board will be needed - often impossible to get - and replacement controller or even just the main chip may be nearly as expensive as a complete new oven.

on Mar 30, 2008 | Kenmore 80412 Microwave Oven

1 Answer

Opening the door tripped breaker a few times, now microwave will not power on.


Sounds like a bad switch should have three primary, secondary, and monitor switch after 5 years change all 3 they are not the same primary and secondary are NO ( normally open ) and the monitor NC ( normally closed ) unit will not come on the fuse on the filter board is blow this usually shorts out the filter board change the switches first and replace fuse may not have to replace filter board hopes this helps.

Apr 06, 2015 | GE Monogram ZE2160SF Convection /...

1 Answer

Microwave oven no power


The main fuse is probably blown.

When replacing, try to determine the cause.

if it has a bad door switch, then the monitor/short switch also must be replaced. On an inverter, replace the power relay as well.

If the fuse holder is not holding the fuse securely, then it will heat and blow.

A failing component in the high voltage circuit can also cause the problem.

Apr 04, 2014 | Whirlpool GH7208XR Convection / Microwave...

1 Answer

Microwave Dead


Having 20 year experience fixing microwaves i know that when the fuse goes that if you can't find a melted wire or overheated components on the circuit board that the high voltage capacitor at the back needs to be replaced. Sometimes you have to replace the magnetron too. You can replace the door switches if you like, microswitches are inexpensive but would only be bad if arced inside so bad that you read over 1 ohm.

Nov 25, 2013 | Microwave Ovens

2 Answers

It just has no power. Nothing happened, I just went to use it and it was dead.


The main fuse is blown, "ceramic type" usually caused by a defective door switch.

Apr 14, 2011 | Maytag MMV4205 Microwave Oven

1 Answer

Internal fuse blown , replaced fuse oven came on for two seconds trips breaker on that circuit . what do you think?


There are three to four switches that monitor that microwave. If any of them are bad it won't work. More then likely it's the monitor switch. There's a primary and a secondary switch. Take the cover off and look for the tech sheet it will show you which ones they are. They are around the door latch area...good luck.

Oct 20, 2010 | Hotpoint RVM1425 Microwave Oven

1 Answer

Now power to microwave


Check the AC fuse and the Primary winding of the Low voltage Transformer.

Jun 27, 2009 | GE JE1540 Microwave Oven

1 Answer

Replacing the fuse of a MCO160UW


A microwave can be dead for many reasons.

It may be the fuse, which is usually located on the floor of the oven behind the control panel or between the door switches.

If the fuse is good, it may be an open thermostat or thermal cutout (TCO) / thermal fuse on or near the magnetron or on top of the cavity / body of the oven.

If it goes dead for a while during or after cooking then comes back on, the magnetron is probably overheating and causing the magnetron thermostat to open.

Then when it cools, it closes the circuit and allows power through again.

When checking thermostats, if it has a hood fan thermostat, that should read open, as opposed to the others, which should read closed.

If it went dead almost immediately after pressing the Start pad, that's usually a shorted high-voltage capacitor.

If it went dead a few seconds after pressing the Start pad, that's usually a failing high-voltage transformer.

If it goes dead or blows the breaker (or GFI) when you plug it in or open or close the door, then there's a problem with a door switch or door switch mount.

If it's intermittent or random, it may be a bad connection, usually on the control board or a loose fuse holder, or even an intermittent fuse.

You should do a continuity test on the fuse while it's in the holder (with the microwave unplugged, of course) then turn the fuse by hand or take it out and put it back in, then test it again.

If you remove the fuse, then press the meter leads against the ends, it can allow internal contact to be made and make a bad fuse appear to be good.

If you or someone you know decide to look into it, we have critical safety information and disassembly information at our site, and our link is at our listing here on FixYa.

There may also be a "mini-manual" hidden inside the unit behind the control panel or hidden on the left side behind the grille, which is very helpful when troubleshooting & testing.

We're happy to help you and we'd appreciate your thoughtful rating of our answer.

Jul 15, 2008 | Magic Chef CMV1000B Microwave Oven

3 Answers

JMC7000ADW Blows circuit breaker


I've had this problem twice with our microwave. The hint to where the problem lies is that the breaker blows when you open the door at times. Inside the microwave are three microswitches; primary and secondary interlock micro switches and an Interlock Monitor switch. The switches are supposed to shut down the microwave if it is running and the door is opened. But, I've found the upper primary switch can stick internal at times and when the door is opened the stuck switch will, because of the way it is wired as a safety switch, cause either the fuse or possibly the main circuit breaker for the oven to pop. The reason the stuck switch blows the breaker or fuse is when the door is opened the interlock switch will cause the neutral wire from the AC power to be applied to the Upper Primary Interlock switch which normally should be open when the door is opened, but if the switch is intermittent or the contacts weld themselves shut the neutral line is connected direct to the "hot" side of the power line through the fuse and thermostat. The first time my microwave failed the switch had melted the contacts together inside the switch and the second time the switch became intermittent and would blow the breaker to the over ever so often. I suspected the switch the second time this happened and utilizing an ohm meter I checked the switch several times by opening and closing the door and once in a while it would remain closed instead of opening when the door was opened. Of course while trouble shooting the power cord to the microwave must be disconnected and use all safety precautions when working around the high voltage areas inside the microwave. I wrote Jenn-Air about the bad switch and the way it is wired into the circuit, but never received any acknowledgement. I suspect these microswitches are under rated for the amount of current that passes through the switch, thus they overheat and eventually arc the contacts together. I hope this helps explain the intermittent problem and could explain many of the intermittent blown fuse problems I see in these internet help sessions

May 09, 2008 | Jenn-Air JMC7000 Microwave Oven

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