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.
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Re: 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.
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First, check the fuse usually located above the display, inside the top lid. You can't see if it's blown, so you must test it for continuity with a meter or self powered test light. Usually fifteen amp, and of the ceramic variety. (available at radio shack type places) If the new one blows instantly, it's likely a door switch shorted out. If it blows after a few seconds, it could be the magnetron gone bad, or internal arcing. The main transformer will sometimes short out, but that's rare.
Be absolutely careful, should your fingers venture around the magnatron connections down below, as there is high voltage and current that can kill you. This warning applies even when it's unplugged!
The door switches operate together, so if one slams the door shut it will often blow the fuse with no other damage. Sometimes the crow-bar switch will sustain damage in the process. Usually, if the switches click individually, they're good. If one doesn't click, it'll almost always be shorted. They're located behind the door catch, inside the unit beside the display board, and a bit hard to access. You will need to reach past the magnatron for this, so be careful.
Q - My microwave seems to shut off every once in a while, what might be wrong? A - Make sure you hear the fan is still operating in your microwave. Next is to make sure the air intake grill on your microwave is not plugged up with air borne dust and dirt. Q - The fan in my microwave oven is not running will this hurt my microwave? A - YES, the fan cools the magnetron and electronics, take the microwave in for service, most fans are not too expensive to replace. Q - My microwave blows the fuse inside itself as soon as I push the start button. A - Usually a shorted high voltage capacitor...see components section.
I have model GE Microwave serial # JVM2070SK02. I start to cook something and it shuts off 5~10 seconds. Keyboard is still lit up, but no clock, fan, light and you cannot operate anything on the key pad. Unplug the unit and it resets. Sometimes it cooks, sometimes it doesn't? It is getting more frequent with the shutting down problem?
If it blows the fuse as soon as you hit the START button, it's almost certainly a shorted high-voltage capacitor.
If it blows a few seconds after you hit the START button, it's probably the high-voltage transformer. You'll possibly also smell a faint electrical burning smell from the rear vent after you shut if off.
Microwave can be very dangerous so it is best to have it looked by a professional
Would appreciate a solved rating for expert advise.
> 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!!!
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.
WARNING: Microwave ovens are the most dangerous consumer appliance to
service due to up to 5,000 V at high current inside. Even with the
power off, there is a HV capacitor that can produce a lethal kick. This capacitor must be discharged before touching anything in the microwave generator circuitry.
DON'T remove the cover yourself unless you fully undertand the SAFETY issues involved in working inside a microwave oven. A microwave oven is possibly THE MOST DANGEROUS common consumer product to service.
About the only "easy" fix would be a blown fuse, if it keeps blowing, don't go any further unless you know what you are doing.
Your likely options are a blown high voltage cap, diode, or the magnetron.
Good luck(but luck has nothing to do with it ;] )