Panasonic microwave blows 20A fuse

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  #1  
Old 07-15-18, 04:47 PM
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Panasonic microwave blows 20A fuse

I have a Panasonic microwave (NN-SN667) that had the internal 20A fuse blown during normal usage. Replaced the fuse, digital display turns on, door opens/closes without issues. Try to microwave something, when I press start, the fuse immediately blows.

Researching on the internet appears that it is the high voltage capacitor that is bad, but it doesn't appear this microwave has that aluminum cylindrical thing. There is mention of a high voltage inverter for this microwave, is that the part that needs replacement?
 
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Old 07-15-18, 05:26 PM
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It could be a door switch out of alignment, a defective/shorted magnetron or the inverter.
The inverter board.... F606Y8X00AP is over $100.
It might pay to get the service manual for it. Usually $10-12 for the download.
 
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Old 06-14-19, 05:28 PM
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I have a Panasonic NN-P295, it stopped working after 2.5 years, 0.5 years out of warranty. This is the second Over The Range Panasonic that has failed in a short period of time, very disappointing.

My latest failure sounds the same as yours, everything works until you press the Start button, then the fuse blows instantly (no 3 second or 23 second delay (indications of specific problems)). I checked the relay's, they were fine. Not wanting to let another Panasonic go to the dump, I checked the thermal cutoff switches for continuity, they were fine. I checked out the other thermal switch, which is open until you heat it with a hair dryer, then it clicks on, it was fine. Heeding all the high voltage cautions/warnings instructions on the internet, I followed the discharging procedure and removed the high voltage inverter board. The service manual says it's a F606Y6G00AP, a Panasonic Technical Bulletin says it's a F606Y8X00AP, and indeed it is a F606Y8X00AP. I discharged the magnetron, and measured the resistance across the terminals, it was good. There were no shorts to ground. The magnets were not cracked.

So all fingers were pointing to the high voltage inverter board. While there's a bridge, IGBT, and a couple of opto isolators on there that you can in theory test, the manual says it's too dangerous, and just to replace the whole unit. Indeed, if the bridge or IGBT are the problem, they are hard to find parts anyhow. So I phoned my local parts dealer, and lo and behold they have F606Y8X00AP in stock... probably because the die so often. They seem to be made in China with chinese writing all over it.

Anyhow, after replacing the board and carefully putting all back together, it works!!! Hopefully another 2.5 years of service before it dies again.
 
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