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Final follow up to: Unit shuts off (JVM1340WW002) and blows fuses
Your answer had high level of experise and I was ready to buy the HV Capacitor, until the Repairclinic.com answer came in and it is as follows (see my cooments back to them when they first pointed to a door switch):
Repairclinic.com (they first blaimed the door switch):
This microwave has 3 door switches, 2 secondary and 1 monitor. From that description it sounds like a bad high voltage component like the magnetron or transformer.
My question: Could they be right about the transformer and magnetron?
My initial response: I appreciate the initial response on below problem description, but need further clarification. As I decribed, I checked the door switches all fine. I was hoping for more meaningfull answer. Though I suspect the HV Cap, the manner in which the micrawave died may or may not be consistant with Ccap failure. The microwave initially started fine but started to die after few seconds (3-5 sec)- you could hear as the power just start go down. After the fuse replacement it would blow it as soon as I hit the "Start" keypad. My question: Can the initial non-instanteneous failure be attributed to HV capacitor problem or is it something else (transformer or magnetron or triac)?
My initial problem description:
The power on my microwave JVM1340WW002 started to go down after few seconds into operation (~5 sec not right away) and then shut down completely. Found that fuse was blown. After replacing the fuse it would shut down as soon as it would start, blowing the fuse again. The High power Capacitor and rectifier show no visible sign of damage. Checked door switch and thermal sensors (two of them - both fine: one is normally open). It leaves either HV Capacitor/Diode, Transformer or Magnetron (still under warranty). I would be inclined to suspect the Capacitor, but the fact that microwave was able to start and died down in few seconds raises doubts. My understanding is that HV cap is there to provide the boost on start up only. Please help.
Your initial response:
In my 20 years of working on microwaves, I have never seen a capacitor fail in any way but a dead short, but it's possible that it's failure may occur in a less abrupt manner.
The internal structure of a capacitor is essentially a rolled up sandwich consisting of two thin layers of foil separated by a very thin insulator.
While a "perfect" capacitor consumes no power, in the real world, things can happen to change that.
A defect could increase the capacitve reactance or other internal resistance and allow internal heat buildup or expansion, which could lead to an intermittent short when it's warmed up a bit.
After a while, the short could become permanent - sort of like arc welding, if you're familiar with that.
So, while it's quite possible that this is the pathology that lead to a fully shorted capacitor, I think that's what you have, no matter how it happened.
Thanks again for you valuable input. I already removed the HV Cap and tried to check it out. Did not get any readings though. Maybe because my meter can only go to 3K max whereas procedure says to set the Ohm to 10-50K scale. While I don?t mind paying for fixing it, the repair people want to charge $90 just to diagnose the problem. Fixing it is additional. It appears that any fix will cost me more than a brand new appliance. The GE JVM 1440 which looks like replacement for JVM 1340 cost around $200. Swapping Cap or Triac is far as I was willing to go with this providing it could easily be identified as problematic. Any other part like Transformer or Magnetron is too expensive to replace (though the Magnetron is under warranty it may require microwave removal). I appreciate all the help you have provided, but as the MicrowaveSvc Tech said, there come a point when, one should either turn it over to a pro or buy a new unit.Thanks again for you valuable input. I already removed the HV Cap and tried to check it out. Did not get any readings though. Maybe because my meter can only go to 3K max whereas procedure says to set the Ohm to 10-50K scale. While I don?t mind paying for fixing it, the repair people want to charge $90 just to diagnose the problem. Fixing it is additional. It appears that any fix will cost me more than a brand new appliance. The GE JVM 1440 which looks like replacement for JVM 1340 cost around $200. Swapping Cap or Triac is far as I was willing to go with this providing it could easily be identified as problematic. Any other part like Transformer or Magnetron is too expensive to replace (though the Magnetron is under warranty it may require microwave removal). I appreciate all the help you have provided, but as the MicrowaveSvc Tech said, there come a point when, one should either turn it over to a pro or buy a new unit.
I have a Kenmore Ultra wave Microwave Hood Combination model number 63684 Never had a problem in 4 years. Went to boil water and in 13 seconds it shuts off. F-9 appears in the time window. Tried several times and the same thing happened. No help with calling Sears. No idea what F-9 means Never got in touch with a live person to ask.I have a Kenmore Ultra wave Microwave Hood Combination model number 63684 Never had a problem in 4 years. Went to boil water and in 13 seconds it shuts off. F-9 appears in the time window. Tried several times and the same thing happened. No help with calling Sears. No idea what F-9 means Never got in touch with a live person to ask.
I have a similar problem with my unit which is an American Heritage and runs on 220-250VAC. It blows the 8A fuse on the input AC 240VAC input side of the power. I checked the Diode and the HV Capacitor and they both are OK. Checked the transformer primary and secondary windings and the readings were OK. Tried several times by replacing the 8A fuse and it blows each time. Then I tried to power it on but disconnecting the input side of the transformer. The light, fan, and timers worked without blowing the fuse. Does this indicate there is a problem with the transformer primary side or the magnetron? There is also another fuse on the HV side of the transformer in series with the HV Capacitor with a value of 1A. This fuse is ok and does not blow. Can you please suggest some other possible reasons for the input fuse to blow? Thanks and God bless you!!! I have a similar problem with my unit which is an American Heritage and runs on 220-250VAC. It blows the 8A fuse on the input AC 240VAC input side of the power. I checked the Diode and the HV Capacitor and they both are OK. Checked the transformer primary and secondary windings and the readings were OK. Tried several times by replacing the 8A fuse and it blows each time. Then I tried to power it on but disconnecting the input side of the transformer. The light, fan, and timers worked without blowing the fuse. Does this indicate there is a problem with the transformer primary side or the magnetron? There is also another fuse on the HV side of the transformer in series with the HV Capacitor with a value of 1A. This fuse is ok and does not blow. Can you please suggest some other possible reasons for the input fuse to blow? Thanks and God bless you!!!
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Re: Final follow up to: Unit shuts off (JVM1340WW002) and...
I have also see the diode open up and cause this problem If the capacitor is not bad and you try and grab the wires you will get a shock! before touching the capacitor, with the unit unplugged short out botth wires together on the capacitor.
Re: Final follow up to: Unit shuts off (JVM1340WW002) and...
> My question: Could they be right about the transformer and magnetron?
It certainly could be the transformer or the magnetron, but I really don't think so.
Not that I'm recommending that an inexperienced or unqualified person should do this - and bearing in mind that any person who would do so must assume ALL liability for injury or damage - here's how I (on a VERY careful day *grin*) would find out:
- I would disconnect the oven's power cord from the wall
- I would remove the outer cover
- I would discharge the high voltage capacitor
- I would look again to be sure the plug is out of the wall
- I would make a careful note of and/or mark the exact connections of the wires going to the HV capacitor
- I would be very careful in case the connectors have positive locks and not yank on them before I push in the locks
- I would disconnect the wires from HV capacitor
- I would set my meter to a medium or high resistance scale and touch one probe to each capacitor terminal and from each terminal to the case of the capacitor
- If either reading held steady at less than infinity I would replace the capacitor, reconnect the wires, reassemble and test
- If neither reading held steady at less than infinity I would reconnect the wires
- I would then make a careful note and/or mark the exact locations of the wires attached to the transformer
- I would then disconnect just the lead which goes from the secondary of the transformer to the capacitor
- I would then remove the other end of that lead wire
- I would then insert a new fuse then plug the microwave into the wall and test it
- If the fuse blew, I would know it's not the capacitor or the magnetron and I would troubleshoot further
- If the fuse did not blow, I would know it's the magnetron or the capacitor (but I just measured the capacitor and it's not shorted!! *grin*)
- I would unplug it again from the wall
- I would install a new capacitor, hook it all back up, install a new fuse, reconnect the wires, and test it again
Sorry to be so stiff about my reply, but I do not want to advise or suggest that an untrained or inexperienced should troubleshoot or work on a microwave oven. The voltages can be instantly lethal.
Good luck and be safe!!!
> By techman >I have also see the diode open up and cause this problem
I guess I could see how an open rectifier could cause a fuse blow, either because of spikes or hash which had been suppressed by the diode, or by somewhat higher overall voltage periodically presented to the magnetron.
But... he said it was initially blowing the fuse after some time, but now it blows upon pressing START. Does that jibe with an open diode? SOMETHING has degraded...
I still say (tech to tech) to ohm the cap, then if necessary remove the HV lead and run it again.
Yes, the HV xfmr would be running unloaded, but it helps narrow it down a bit.
You and I have the luxury of spare parts to try. *grin*
We both certainly want the customer to fix his problem without buying a part he doesn't need, and without buying the farm!
I think we'd postulated all we can, and it's time for the owner to make the call. If he has that much uncertainty, maybe he should turn it over to a pro.> By techman
>I have also see the diode open up and cause this problem
I guess I could see how an open rectifier could cause a fuse blow, either because of spikes or hash which had been suppressed by the diode, or by somewhat higher overall voltage periodically presented to the magnetron.
But... he said it was initially blowing the fuse after some time, but now it blows upon pressing START. Does that jibe with an open diode? SOMETHING has degraded...
I still say (tech to tech) to ohm the cap, then if necessary remove the HV lead and run it again.
Yes, the HV xfmr would be running unloaded, but it helps narrow it down a bit.
You and I have the luxury of spare parts to try. *grin*
We both certainly want the customer to fix his problem without buying a part he doesn't need, and without buying the farm!
I think we'd postulated all we can, and it's time for the owner to make the call. If he has that much uncertainty, maybe he should turn it over to a pro.
Now that I think of it, I do seem to remember that when it has an open diode the mag groans louder... at least... It's been a LONG time since I had an open diode...Now that I think of it, I do seem to remember that when it has an open diode the mag groans louder... at least... It's been a LONG time since I had an open diode...
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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?
this is a list of possible causes. Defective interlockswitch or misaligned door, shorted HV capacitor, shorted HV diode, these are top three things that will cause the main fuse to blow when you start the microwave. the humming you hear is from the diode or magnetron. To be safe you have to discharge the HV capacitor here is what you'll need and how to do it. You will need a resistor 100K ohms 25watts or a a string of smaller ones to add up to that. Solder one end of the resistor to a well insulated clip lead of 2 to 3 ft. long.Solder the other end toa well insulated contact point as a #14bare copper wire about 2 inches long and secure the resistor to a piece of 2ft pvc pipe with electrical tape clip the other end of the clip lead ground to a unpainted spot on the chassis of the microwave and use the pvc pipe as a handle and touch each side of the capacitor to discharge a couple seconds at a time switching back and forth. after a minute or so take a well insulated screwdriver and touch each side of the capacitor at the same time and if you have no arcing, popping and such it is safe to take off and replace
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Sorry to read about your problem, I hope this helps you out.
here are some issues, but you still maybe under warranty.
Blown fuse in HV transformer primary circuit or HV fuse (if used).
Bad connections (particularly to magnetron filament).
Open thermal protector or thermal fuse.
Open HV capacitor, HV diode, HV transformer, or magnetron filament.
Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
Damaged protective VDR from filament to chassis (not commonly used).
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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Sorry to read about your problem, I hope this helps you out.
Here are some problems you can have
Blown fuse in HV transformer primary circuit or HV fuse (if used).
Bad connections (particularly to magnetron filament).
Open thermal protector or thermal fuse.
Open HV capacitor, HV diode, HV transformer, or magnetron filament.
Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
Damaged protective VDR from filament to chassis (not commonly used).
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's. take the time to rate us.Thanks and good luck
Sorry to read about your problem, I hope this helps you out.
Here are some issues you can have
Blown fuse in HV transformer primary circuit or HV fuse (if used).
Bad connections (particularly to magnetron filament).
Open thermal protector or thermal fuse.
Open HV capacitor, HV diode, HV transformer, or magnetron filament.
Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
Damaged protective VDR from filament to chassis (not commonly used).
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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Sorry to read about your problem, I hope this helps you out. you may one of these issues.
Blown fuse in HV transformer primary circuit or HV fuse (if used).
Bad connections (particularly to magnetron filament).
Open thermal protector or thermal fuse.
Open HV capacitor, HV diode, HV transformer, or magnetron filament.
Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
Damaged protective VDR from filament to chassis (not commonly used).
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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Sorry to read about your problem, I hope this helps you out.
You can many different issue's
Blown fuse in HV transformer primary circuit or HV fuse (if used).
Bad connections (particularly to magnetron filament).
Open thermal protector or thermal fuse.
Open HV capacitor, HV diode, HV transformer, or magnetron filament.
Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
Damaged protective VDR from filament to chassis (not commonly used).
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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Sorry to read about your problem, I hope this helps you out.
No heat but otherwise normal operation.
Possible causes:
Blown fuse in HV transformer primary circuit or HV fuse (if used).
Bad connections (particularly to magnetron filament).
Open thermal protector or thermal fuse.
Open HV capacitor, HV diode, HV transformer, or magnetron filament.
Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
Damaged protective VDR from filament to chassis (not commonly used).
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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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 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.
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
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)
The HV capacitor or the HV diode may be in short, check these parts, discharge the capacitor before touching anything. Maybe something is shorted to ground.
In my 20 years of working on microwaves, I have never seen a capacitor fail in any way but a dead short, but it's possible that it's failure may occur in a less abrupt manner.
The internal structure of a capacitor is essentially a rolled up sandwich consisting of two thin layers of foil separated by a very thin insulator.
While a "perfect" capacitor consumes no power, in the real world, things can happen to change that.
A defect could increase the capacitve reactance or other internal resistance and allow internal heat buildup or expansion, which could lead to an intermittent short when it's warmed up a bit.
After a while, the short could become permanent - sort of like arc welding, if you're familiar with that.
So, while it's quite possible that this is the pathology that lead to a fully shorted capacitor, I think that's what you have, no matter how it happened.
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.
Thanks again for you valuable input. I already removed the HV Cap and tried to check it out. Did not get any readings though. Maybe because my meter can only go to 3K max whereas procedure says to set the Ohm to 10-50K scale. While I don?t mind paying for fixing it, the repair people want to charge $90 just to diagnose the problem. Fixing it is additional. It appears that any fix will cost me more than a brand new appliance. The GE JVM 1440 which looks like replacement for JVM 1340 cost around $200. Swapping Cap or Triac is far as I was willing to go with this providing it could easily be identified as problematic. Any other part like Transformer or Magnetron is too expensive to replace (though the Magnetron is under warranty it may require microwave removal). I appreciate all the help you have provided, but as the MicrowaveSvc Tech said, there come a point when, one should either turn it over to a pro or buy a new unit.
I have a Kenmore Ultra wave Microwave Hood Combination model number 63684 Never had a problem in 4 years. Went to boil water and in 13 seconds it shuts off. F-9 appears in the time window. Tried several times and the same thing happened. No help with calling Sears. No idea what F-9 means Never got in touch with a live person to ask.
I have a similar problem with my unit which is an American Heritage and runs on 220-250VAC. It blows the 8A fuse on the input AC 240VAC input side of the power. I checked the Diode and the HV Capacitor and they both are OK. Checked the transformer primary and secondary windings and the readings were OK. Tried several times by replacing the 8A fuse and it blows each time. Then I tried to power it on but disconnecting the input side of the transformer. The light, fan, and timers worked without blowing the fuse. Does this indicate there is a problem with the transformer primary side or the magnetron? There is also another fuse on the HV side of the transformer in series with the HV Capacitor with a value of 1A. This fuse is ok and does not blow. Can you please suggest some other possible reasons for the input fuse to blow? Thanks and God bless you!!!
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