Question about Microwave Ovens

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I have a Samsung CS1660 microwave. The slow-blow fuse between the HV transformer and the capacitor has blown. What is the easiest way to determine what went wrong.

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  • 3,740 Answers

Sometime the fuse will just blow bcause someone slowly opened the door without pressing STOP or PAUSE first. The door interlock switch at that point will blow the fuse.

Usually the reason the fuse blows is that the HV Diode has failed. You check this with a multi meter on resistance by reading across the 2 terminals AFTER making sure the capacitor no longer has a charge on it by grounding across the 2 capacitor terminals at least 3 times. The diode will read continuity in one direction only. (reversing the leads)

Also the HV capacitor can have failed by shorting out.

The HV Cap should show a jump on an analog meter as you reverse the leads then return to infinity.

Lastly the Magnetron can have failed. (Short)

All of the above are checked using an analog multimeter. Nothing fancy... a $5.00 meter will do the trick.

The replacement fuse will either be 15 A or 20 A. Look at the markings on the old fuse and replace it with a like fuse. HOWEVER... if any of the above problems still exist the fuse will just blow again.


Thanks for using FixYa!

Kelly

Posted on May 01, 2010

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My one year old microwave just stopped working. The light is on, but nothing else.


Sorry to read about your problem, I hope this helps you out.

here are some issues, but you still maybe under warranty.
  1. Blown fuse in HV transformer primary circuit or HV fuse (if used).
  2. Bad connections (particularly to magnetron filament).
  3. Open thermal protector or thermal fuse.
  4. Open HV capacitor, HV diode, HV transformer, or magnetron filament.
  5. Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
  6. Damaged protective VDR from filament to chassis (not commonly used).
  7. Defective HV relay (not commonly used).
Microwaves must be serviced by technicians due to the inherent dangers involved in repairing these appliances. Internal capacitors can retain a lethal electrical charge even though the unit is completely unplugged. A microwave radiation leakage test must be performed on the unit following any internal component repair.

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Jan 05, 2011 | Goldstar MV-1501 Microwave Oven

2 Answers

Micro wont heat. fix or replace? what could be the prob?


Sorry to read about your problem, I hope this helps you out.

Here are some problems you can have
  1. Blown fuse in HV transformer primary circuit or HV fuse (if used).
  2. Bad connections (particularly to magnetron filament).
  3. Open thermal protector or thermal fuse.
  4. Open HV capacitor, HV diode, HV transformer, or magnetron filament.
  5. Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
  6. Damaged protective VDR from filament to chassis (not commonly used).
  7. Defective HV relay (not commonly used).
Microwaves must be serviced by technicians due to the inherent dangers involved in repairing these appliances. Internal capacitors can retain a lethal electrical charge even though the unit is completely unplugged. A microwave radiation leakage test must be performed on the unit following any internal component repair.

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Jan 05, 2011 | Kenmore 63792 Microwave Oven

1 Answer

It's not heating food, sounds louder than normal and smells like something possibly electrical is burning (or just getting too hot), but it looks as if it's working (lights up, tray moves inside, timer...


Sorry to read about your problem, I hope this helps you out.

Here are some issues you can have
  1. Blown fuse in HV transformer primary circuit or HV fuse (if used).
  2. Bad connections (particularly to magnetron filament).
  3. Open thermal protector or thermal fuse.
  4. Open HV capacitor, HV diode, HV transformer, or magnetron filament.
  5. Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
  6. Damaged protective VDR from filament to chassis (not commonly used).
  7. Defective HV relay (not commonly use
Microwaves must be serviced by technicians due to the inherent dangers involved in repairing these appliances. Internal capacitors can retain a lethal electrical charge even though the unit is completely unplugged. A microwave radiation leakage test must be performed on the unit following any internal component repair.

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Jan 04, 2011 | Maytag MMV5207BAW Microwave Oven

2 Answers

It will run but it won't heat. It also makes a funny "humming" sound and smells like burning plastic.


Sorry to read about your problem, I hope this helps you out.
you may one of these issues.
  1. Blown fuse in HV transformer primary circuit or HV fuse (if used).
  2. Bad connections (particularly to magnetron filament).
  3. Open thermal protector or thermal fuse.
  4. Open HV capacitor, HV diode, HV transformer, or magnetron filament.
  5. Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
  6. Damaged protective VDR from filament to chassis (not commonly used).
  7. Defective HV relay (not commonly used).
Microwaves must be serviced by technicians due to the inherent dangers involved in repairing these appliances. Internal capacitors can retain a lethal electrical charge even though the unit is completely unplugged. A microwave radiation leakage test must be performed on the unit following any internal component repair.

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Jan 04, 2011 | Maytag MMV5156AAS Microwave Oven

1 Answer

Microwave activate but will not heat food all light and buttons work but will not heat up


Sorry to read about your problem, I hope this helps you out.

You can many different issue's
  1. Blown fuse in HV transformer primary circuit or HV fuse (if used).
  2. Bad connections (particularly to magnetron filament).
  3. Open thermal protector or thermal fuse.
  4. Open HV capacitor, HV diode, HV transformer, or magnetron filament.
  5. Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
  6. Damaged protective VDR from filament to chassis (not commonly used).
  7. Defective HV relay (not commonly used).
Microwaves must be serviced by technicians due to the inherent dangers involved in repairing these appliances. Internal capacitors can retain a lethal electrical charge even though the unit is completely unplugged. A microwave radiation leakage test must be performed on the unit following any internal component repair.

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Jan 04, 2011 | GE Spacemaker JVM1640SJ Microwave Oven

1 Answer

GE JVM1440 will not heat.


Sorry to read about your problem, I hope this helps you out.

No heat but otherwise normal operation.
Possible causes:
  1. Blown fuse in HV transformer primary circuit or HV fuse (if used).
  2. Bad connections (particularly to magnetron filament).
  3. Open thermal protector or thermal fuse.
  4. Open HV capacitor, HV diode, HV transformer, or magnetron filament.
  5. Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
  6. Damaged protective VDR from filament to chassis (not commonly used).
  7. Defective HV relay (not commonly used)
Microwaves must be serviced by technicians due to the inherent dangers involved in repairing these appliances. Internal capacitors can retain a lethal electrical charge even though the unit is completely unplugged. A microwave radiation leakage test must be performed on the unit following any internal component repair.

I tried to help you. Please help me and Rate/Vote on my response. We take the time to answer your question. take the time to rate us.Thanks and good luck

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Jan 01, 2011 | GE JVM1440 Microwave Oven

1 Answer

Model 721.64282 microwave/convection oven - microwave not heating and making a loud noise. convection oven works


No heat but otherwise normal operationA shorted HV diode, magnetron, or certain parts of the HV wiring would probably result in a loud hum from the HV transformer but will likely not blow the main fuse. (However, the HV fuse - not present on most domestic ovens - might blow.)
If the main power fuse is located in the primary of the high voltage transformer rather then at the line input, the clock and touchpad will work but the fuse will blow upon initiating a cook cycle. Or, if the fuse has already blown there will simply be no heating action once the cook cycle is started. There are other variations depending on whether the cooling fan, oven light, and so forth are located down stream of the fuse.

Some models may have a separate high voltage fuse. If this is blown, there will be no heating but no other symptoms. However, high voltage fuses are somewhat rare on domestic ovens.

A number of failures can result in the fuse NOT blowing but still no heat:


  • Bad connections - these may be almost anywhere in the microwave generator or the primary circuit of the HV transformer. A common location is at the crimp connections to the magnetron filament as they are high current and can overheat and result in no or intermittent contact. See the section: See the section: Testing the magnetron.
  • Open thermal protector - usually located on magnetron case. Test for continuity. It should read as a dead short - near zero ohms. See the section: Testing thermal protectors and thermal fuses.
  • Open thermal fuse - some ovens have one of these in the primary circuit. It may be in either connection to the HV transformer or elsewhere. Test for continuity. It should read as a dead short - near zero ohms.
  • Open HV capacitor - see the section: Testing the high voltage capacitor. A shorted HV capacitor would likely immediately blow the fuse.
  • Open HV diode - see the section: Testing the high voltage diode.
  • Open magnetron filament - This failure may also be due to loose, burnt, or deteriorated press (Fast-on) lugs for the filament connections and not an actual magnetron problem. See the section: Testing the magnetron.
  • Open winding in HV transformer. See the section: Testing the high voltage transformer.
  • Defective HV relay. A few models use a relay in the actual high voltage circuitry (rather than the primary) to regulate cooking power. This may have dirty or burnt contacts, a defective coil, or bad connections
  • Shorted HV diode - see the section: Testing the high voltage diode.
  • Short or other fault in the magnetron - see the section: Testing the magnetron.
  • Short in certain portions of the HV wiring. See the section: Testing and repairing the wiring and connections.

Depending on design, a number of other component failures could result in no heat as well including a defective relay or triac, interlock switch(s), and controller.


If you are interested in doing it yourself the following link will help : Microwave Repair Manual

(**All the above references to tests are found here)

Oct 21, 2010 | Kenmore 63663 Microwave Oven

1 Answer

I have a Samsung microwave model SMH7177STE/BE. Will only heat a few minutes before and shut off, now there is no heat. I am a licensed elect. but no experience with microwaves and having difficulty...


Its tripping a high limit most likely. Be careful there is 2100 to 4000 volt high side with a capacitor if its not an inverter. The standard components consist of noise board, fuse, touch panel and power controller, high limits, door switches, whipper motor, fan, transformer, capacitor, transformer, magnetron, diode, plate rotator.
Discharge cap (for safety and further testing).. Test fuse; if fuse tests blown test door switches first. Test limits. Check amp draw with slow blow fuse; open door to stop unit and again discharge capacitor. Test resistance to ground on whipper, fan, magnetron, light. Test resistance lead to lead (measurable on motors/coils/magnetron). Test capacitor in ferrads, compare to spec on print. Check diode forward and reverse. Test output voltage from power control board to transformer. Test transformer coils.
Best of luck and play safe; dont test voltage output from the transformer, voltage at capacitor or magnetron.

Aug 03, 2010 | Samsung Microwave Ovens

1 Answer

Unit shuts off (JVM1340WW002) and blows fuses


Generally speaking, if the high voltage capacitor is shorted, the fuse will blow as soon as you hit the START pad. When the HV cap fails, I've never seen one do anything but short. If it's a few seconds or so into cooking, it's usually the high-voltage transformer. There may or may not be a burning smell. The cooling fan often will dissipate the smell. What can happen to the transformer is an expansion of the windings to the point where a couple of hot spots eventually make bare spots which touch, then the short causes the fuse to blow. When it cools, they aren't shorting anymore. It's possible it's the mag or something else, but not too likely. You can (carefully!) disconnect the primary leads from the HV transformer then run the oven, making sure the wires are free and clear. If the fuse blows, the problem is in the low-voltage side. If it doesn't the trouble is in the HV side. If you broke a seal (tamper tag) or left any other evidence that you were inside the microwave, your warranty will be voided. Some parts may be covered, but the labor warranty usually expires sooner. Be careful.

Nov 06, 2006 | GE JVM1440 Microwave Oven

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