Question about Frigidaire FFMV162LW Microwave Oven

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20 amp fuse blows in micro wave

Door switches test good, cap good, HV transformer good

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Posted on Jan 02, 2017

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MicrowaveSvc
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SOURCE: Servicer with a PLMV169DCD Fuse blowing Problem

For future reference, we regularly repair such control boards and displays for customers nationwide by mail for $39.95 postpaid in about a week or so with a one-year guarantee.

Here's the main service manual. Other versions are here and here.

It may be grease inside one of the switches or arcing conductors (usually due to opening the door while it's cooking) making it sticky.

This was made by Sharp, so the side panel should come off each interlock switch for inspection.

But looking at the schematic, the monitor switch cannot come into play under normal circumstances unless the door is shut and the secondary interlock (relay RY2 on the control board) is closed and (oddly, if the published schematic is to be believed) if the oven lamp relay RY1 is closed .

Everything seems to point to a bizarre problem like maybe an intermittent short of a wire to the chassis, perhaps where a wire passes through a hole or guide in the sheet metal.

Also, you might consider unplugging the hood vent motor and trying it.

Did you try it with the oven powered from another outlet?

Also be sure the neutral and hot are not reversed at the outlet and that the line voltage is correct.

Sometimes a loose neutral can be a factor. Test outlets in several area of the house to see if some are high and some are low. This can be dangerous, and the power company must be called.

If there is anything else on the same breaker, that can be a factor.

Good luck!

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

William E. Miller
prototech@usa.net
http://www.microwavedisplay.com

Posted on Nov 29, 2009

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1 Answer

GE Profile Microwave Fuse Keeps Blowing


First of all, be sure your AC line voltage is correct at the outlet, at between 105 and 125VAC. If not, call an electrician.

There should be a technical sheet hidden behind the controller or behind the grille or the oven. It's helpful when troubleshooting. If you don't find yours, e-mail me for a copy.

Next take a look at the fuse holder connections and wire terminal connections on the filter board where the fuse is.

Loose or charred connections can increase heat and resistance, leading to a melted fuse.

Also look at the terminals on the upper door switch, magnetron thermostat, and oven thermostat for the same reasons as above. (You'll probably have to remove the oven from the wall to get to the oven thermostat. Your installation instructions are here.)

It's not likely the trouble, but you can eliminate monitor interlock trouble by disconnecting one wire (probably the black one) from the middle door switch and trying your test again. (Ignore the bottom door switch altogether.)

For more free DIY and other help & advice, feel free to contact me.

William E. Miller, AS-EET
pupista@gmail.com
http://www.microwavecontrol.com
Microwave Oven Control Panel Repair Nationwide
"Recycling by repairing since 1982"

Mar 14, 2017 | GE Microwave Ovens

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

I keep blowing my 20 amp fuse, replaced mag tube and diode


Check the HV capacitor. It may be short circuited.
Also check the door switches. One of the switches (the monitor switch) is connected directly across the power and is there to blow the fuse in the event that the timing of the door switches are incorrect.
The monitor switches on Panasonic micros will also short.

Jan 04, 2011 | Microwave Ovens

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

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.


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

May 01, 2010 | Microwave Ovens

1 Answer

Microwave stopped heating after being cleaned (could be co-incidence). Besides not heating appeared to run properly. Let sit for a day hoping something was wet and would dry, tried heating glass of water...


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 when you plug it in or open or close the door, then there's a problem with a door switch or door switch mount.

But you might replace the fuse and do another quick heating test to see if it blows again. If so, you'll need to do some checks.

Here are some links you or someone you know can use for test help, but read their safety warnings first:

http://www.gallawa.com/microtech/cap_test.html
http://www.gallawa.com/microtech/diode.html
http://www.gallawa.com/microtech/xformer.html
We're happy to help and we appreciate your thoughtful rating of our answer.

William E. Miller, AS-EET
prototech@usa.net
http://www.microwavedisplay.com

May 12, 2008 | Microwave Ovens

1 Answer

Ge Spacemaker microwave jvm240 wv Micro hood combo.


sounds to me like the magnatron has shorted out. i don't know of a way to test them unless you have some high dollar equipment. a continuity test prob wont tell you anything. what reading did you get on the cap when you tested it?

Jan 05, 2008 | GE Spacemaker JVM1640SJ Microwave Oven

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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