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.
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