Top 20 Panasonic NN-T990SA Microwave Oven Questions & Answers

Question edited for clarity. Question moved from Televisions https://www.google.com/search?q=Panasonic+NN9853+control+panel+schematic https://www.google.com/search?q=panasonic+nn+9853+service+manual+pdf https://www.fixya.com/support/r29874712-repairing_microwave_ovens ..

open top cover and replace lamp

you have to remove the plug and then the outer casewhich is 4-5 screws on the back,you will find a air duct on the left hand side of the magnetron which is a metal box with two wires on the bottom.the bulb hosing is kept in with a screw and a metal tab,undo the screw and remove the two wires and that is the unit you have to replace,it is called a cap less bulb as it is one unit,reassembly is the reverse.hope this helps regards les

There are a number of possible causes. The following link will take you to a page with the diagnostic flow chart that you can use to troubleshoot this issue: Microwave Fault Codes This customers review of that issue may also be of some help: Customer Reviews Panasonic NN T945SF 2 2 Cubic Foot 1250 Watt Microwave...

MAY BE DOOR SWITCHES

Plug a lamp into the wall receptical, if it works! the main fuse in the microwave has blown. Unplug, and remove the top "several screws" check under the keypad and follow wires to the circuit board, look for a silver rectangular capacitor, take a screw driver and short the two points to remove any residual voltage. Now look for a small fuse "clipped" pop with screwdriver and replace with the same current rating, assemble unit because lethal voltages are present when powered on.

Since no model number was posted, I have to give a general answer.Since it was posted under Panasonic, I'll assume it's a Panasonic.See if one of these describes what's happening:

• Put in time, push start and unit runs for 2 seconds, relay clicks, unit goes off. Cook time on display goes off and clock time comes back. Bad upper interlock switch and charred connector

If so, see http://031d26d.namesecurehost.com/mwd/safety.txt http://031d26d.namesecurehost.com/mwd/disassembly.txt http://031d26d.namesecurehost.com/mwd/doorsw.txt Otherwise, if the digital programmer circuit / controller does not get a feedback signal from the inverter for a period of 3 seconds, the controller will stop the cook cycle. It may be a loose connection in the wiring between the inverter, magnetron, and/or control board, or maybe one of those components has failed.If it stops after 7 seconds, it has a problem with the inverter.Due to the lethal voltages used and produced in inverters, I do not recommend that an inexperienced person work on these.

This sounds like a magnetron problem, if it gets to hot, there is a special thermal fuse that will open up if it senses abnormal temperature rise from the magnetron and after a cool down period it will reset itself. In rare cases I have known the thermal fuse to become defective and cut out prematurely. My feeling is replace the oven! because by the time you get a appliance repairman in for a sevice call and parts you probably could have bought a new microwave oven.

The problem is an engineering defect. The mechanism that engages the door latch is mounted to a steel plate that is "L" shaped and when you close the door it pushes against and bends this plate out of position. After a while the metal plate fatigues and stays bend out of position and the door stops engaging and locking so the two safety switches inside don't get depressed. Result door won't lock and light stays on. I had to re-engineer it by cutting the tube of a pen to size and placing it in as a support bracket to put pressure on the plate so it won't bend anymore. My wife was going to throw it in the trash. Note of caution: I did cut my hand in several places trying to get the bottom cover on and off the microwave as the metal edges are razor sharp!!! I love this microwave it is my second one.

your magnetron is the heating element. it sends out microwaves that jiggle the water molecules inside the food causing them to heat. this is whats malfunctioning causing your problem. youll have to have a technician replace it

The oven shuts down almost immediately after the inverter board - the one that powers the magnetron - gets activated. This is a big fault, repairing it can be done strictly only by a specialized repair shop and because of that it will be expensive.
So yes, i think it's time to cut your losses and get a new one.

If you were to log on to the manufacturer's web site, I think you will be pleasantly surprised as usually one is able to download, by model number, Customer Instruction Manuals, list of Dealers for spare part supplies as required.

Just Google the manufacturer's name and follow the links. Make certain you are directed to the manufacturer's web site as some search engines direct you to other sites and they charge for the information that is normally free of charge.

I hope this helps.

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Here is a tip that will help you to figure out what is wrong with your Microwave Oven....

Microwave Oven Basic Troubleshooting Tips

heatman101

replace magnetron

check the thermistor on the side of the magnetron tubes body, its usually held on by 2 small screws,it's about 1/2" round and has 2 wires on tabs coming out of it, remove thermistor & wires and clip on ohm-meter and heat the thermistor with a match and see how fast it clicks and the meter goes to infinite from a short circuit which will when in circuit shut power off to the tube it's a type of temperature safety switch for the magnetron tube and it or the tube are faulty, also carefully check the tubes body after operation and cutout and see how hot tube is,it could be the tube going out,but i think it will be the thermistor in the end because if the tube gets that hot that quick it would blow the units fuse due to excessive current draw

To allow us to help you effectively (at no charge), please post a NEW problem to FixYa, and please include your brand name and the full model number from the tag in or on the unit, as well your symptoms "Microwave turns on for 5 seconds, then shuts off".

Please also not whether the display stays on or shuts off.


The object you're describing is the waveguide cover. It needs to stay clean and secure. If it's damaged, it will need to be replaced.

It provides critical protection for the magnetron.

If it stops at 16 seconds and is a sensor model, it probably has a defective humidity sensor.

If it stops after 22 seconds, that means the controller has detected a problem, usually a problem with the inverter, controller, magnetron, or a bad connection from one or the other.

Due to the lethal voltages used and produced in inverters, I do not recommend that an inexperienced person work on these.

You can find an authorized Panasonic servicer here.

In Canada, you can find an authorized Panasonic servicer here.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

To allow us to help you effectively (at no charge), please post a NEW problem to FixYa, and please include your brand name and the full model number from the tag in or on the unit, your exact symptoms, as well as the answers to these questions:

- How long does it run until it stops?

- Is there and error or fault code in the display, such as H97, H98, etc.?

Nothing special in there. As long as the paint is not flaking into the food you are ok, Be aware that bare metal could begin to arc. There is special microwave paint available but it will not match and look bad unless you redo the entire interior.
Eric