Question about Panasonic NN-S543BFW Microwave Oven

1 Answer

Blows line fuse

Unit is approx 3yrs old; the magnatron was replaced under warranty w/in a few months of intial use. The symptoms are: magnatron shows no resistance to casing, filament is not open (measures less than .3 ohms), no visible signs of arcing, had recently shown signs of intermitt door swith - could have been physical latch/position failure as pushing on door harder was good remedy. Never really cared much for this oven - it was a gift. The oven this replaced was a Gen-Air/Amana? that was built like a tank, & lasted approx 15-20yrs. It's the only device in my home that causes interference in bluetooth audio devices - probably from the inverter ckt. If I could confirm a defective magnetron, it's dumpster fill!
Any advice?

R. Munn

Posted by on

  • Richrad D. Munn Mar 28, 2008

    After reading the notice on top of the cook cavity, I suspected there might be a problem w/the interlock or monitor switche(s). The notice says all four safety switches must be replaced if the line fuse is blown due to a defective monitor switch - a bit OSHAish..., but supports the possibility of a misaligned or defective switch causing the line fuse to blow.

    I purchased a Sharp Carosel oven today, and will check all of the switches in the Panasonic before giving up on it - will probably keep it for a spare if it is a switch. This particular Panasonic does not have the usual HV "can type" capacitor, & the two HV diodes check OK. I'll post the outcome when I have a chance to bench it again.

    Thanks for your input - it squares w/what I was thinking.



  • Richrad D. Munn Nov 30, 2009

    I recently got back to the job of repairing the oven in question - just couldn't bring myself to toss it. After all, it is one, if not the only, oven that actually adjust the magnetron output level for percentage cooking, rather that proportionate on/off cycling. The problem I found was a shorted IGBT on the inverter board (Mouser p/n 757-GT60N321[Q]). The cost w/shipping was about $18.00. I replaced that & the open 18amp type abc fuse and all is well. BTW, This oven needs a 20amp house ckt for proper operation.



1 Answer

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 10 achievements.


    An expert that got 5 achievements.


    An expert who has achieved Level 3.

  • Master
  • 518 Answers

Check the resistance of the capacitor across the cap terminals and to ground. It should be open. Also check the diode for a short. Lastly, on some models a defective or misaligned door switch can blow fuses.

Hope that helped...


Posted on Mar 28, 2008


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

A 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
The service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
Good luck!

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Error code F81

A short somewhere and bad if it blows instantly--a shop repair as could be control problem or bad inverter(power for the unit) or even a bad magnatron---someone who knows their way around in this type of unit would have to make some tests---both the inverter board and the magnatron are over 100 each parts.

Jun 16, 2012 | Panasonic NE2157 - Pro I Microwave Oven,...

7 Answers

Microwave runs but will not heat(unit is approx. 5yrs old)

the problem may be with your thermostat check that ,and repair it

Jul 03, 2008 | Microwave Ovens

1 Answer

HVM1750 won't heat

The magnatron is likely to be the problem... though I have seen the fuses go , they usually follow the magnatron.
If your unit is under 5 years old , the Mag is covered under warranty and all you need to do is contact GE at

with the serial number of your unit and they will send you the replacement magnetron imediately and free of charge.

You are responsable to have the part installed , but there are videos on Utube that will walk you thru it no problem.

Sep 30, 2011 | GE HVM1750DMBB / HVM1750DMWW 1000 Watts...

2 Answers

I have a panasonic nw -h665 Microwave. 3 months old. It just does nothing. Fuse Maybe Blown? and where is it ?

3 Months old? Under warranty surely. Just call Panasonic Repair Service for a free repair.

There are fuses in there but they don't fail for no reason.

Jan 14, 2011 | Microwave Ovens

1 Answer

Maytag 2 yrs old. Completely dead - like getting

There is usually a 125V, 20 AMP line fuse inside the microwave, mounted at the point where the power cord enters the back of the unit. Unfortunately, you will need to uninstall the oven (if this is an over the range model), UNPLUG it and remove the exterior case to access. The case comes off in various ways depending on manufacture and model. I found this wiring diagram at based on the model number you listed this question under:

This model has TWO potential causes. The line fuse or the Thermal Cut-Out (Thermostat) for the Magnetron. The line fuse is connected in line with the power cord inside the unit and is listed as part of item 26 under the "Cabinet-Base-Cavity" heading.

The Magnetron Thermostat is listed as item 6 (part number 56001028) under the same heading. If you managed to overheat the oven any time recently, you may want to check the thermostat to see if it is still good. It should read 0 ohms when measured out of the circuit across the terminals.

If the line fuse is blown, you can usually purchase a box of fuses at a hardware store for just a little more than what the manufacturer charges for a single fuse. 125V, 20AMP Ceramic Slow Blow fuses are recommended.

If you have any questions, or need additional assistance troubleshooting, please post back and let me know. I hope you find this information helpful.

NOTE: Make sure you take any resistance readings with the microwave UNPLUGGED and the component under test isolated (removed) from the circuit. These ovens can blow a fuse by simply sitting idle. This can occur from any power fluctuations, brown outs, voltage spikes, etc. Or, it could be the symptom of a component that may have failed. If you find the internal fuse blown and replace it, only to have it blow again, you have a more significant problem than a simple blown fuse.

May 24, 2010 | Maytag MMC5000 Microwave Oven

1 Answer

Everything else seems to work fine but when I take

Magnatron has failed, possible internal fuse to the Magnatron,or the Magnatron itself has gone bad.
Both are replaceable, but the microwave will have to be taken down to gain access to these parts to be serviced.
Now, depending on the age of the unit, it may not be wise to invest the cost for this repair, unless, is it still under the manufactures 1 year warranty or did you purchase an extended service contract on this unit?
Good Luck !

May 02, 2010 | Maytag MMV4205 Microwave Oven

1 Answer

Oven stopped heating; everything else seems to be working. i dont notice difference in sound when turned on model JVM1642BB 003 man date july 2000

The symptom that you have described sounds like the magnatron has failed, the microwave oven looks to be approx. over 9 years old, at that age and with a failed magnatron it is not cost effective to replace the part, it would be best to replace the microwave oven at this point. Good luck!

Nov 26, 2009 | GE Spacemaker JVM1640SJ Microwave Oven

1 Answer

Viking Microwave Model VMOC205SS little over 4

9 amps is approx. correct. Does magnatron make an odd sound when running? If not, you will need to discharge cap then clean terminals with alcahol. Replace diode as well. Should run correctly.If blows again, replace magnatron. Suggest you put a 12 amp fast blow fuse in circuit and nor a 20 fuse.If you dont have a grill or an oven, use a 10 amp fuse.

Sep 17, 2009 | Viking VMOC205SS Microwave Oven

2 Answers


Is the unit under warranty? If not, you can try to remove the cover and see if there is a blown fuse in the section that powers the Magnetron. How old is the unit? Typically, no heating of food, indicates a bad Magnetron (tube).

Good Luck,

- Jim

Jan 24, 2008 | Hotpoint RVM1425 Microwave Oven

1 Answer

GE JVM1650

The owner's manual will give you the warranty length. If you don't have yours, you can find it here:

You really need to call GE on this. Only they can answer if they will still cover it. GE Answer Center -800-626-2005, 24 hours a day, 365 days a year.

Otherwise, it may fall under your State's lemon laws. You can contact the Attorney General's office, usually via (where xx is your State's 2-letter abbreviation).

Nov 04, 2007 | GE JVM1650 1000 Watts Microwave Oven

Not finding what you are looking for?
Microwave Ovens Logo

95 people viewed this question

Ask a Question

Usually answered in minutes!

Top Panasonic Microwave Ovens Experts

William Miller
William Miller

Level 3 Expert

9098 Answers

Donald DCruz
Donald DCruz

Level 3 Expert

17130 Answers


Level 2 Expert

225 Answers

Are you a Panasonic Microwave Oven Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides