Question about Panasonic NN-T993SF Microwave Oven

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T993 - Positive Lock Switch ?

NN-T993SF 1350 WattsThe turntable and fan (NOT the magnetron) run when I open the door. I think the door interlock is sticking, Seems to work fine when the door is closed. 5 years old and just started yesterday.

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  • Panasonic Master
  • 8,820 Answers

This is usually caused by either a bad door switch, a loose door switch mount (which are pretty simple problems to fix) or occasionally a problem on the control panel.

Even though a door switch clicks, it may still be bad inside. Its continuity must be checked.

Door switch or mount trouble can be caused by slamming the door or by opening the door while it's cooking without hitting the Stop pad first.

There are plastic mounts inside the microwave which hold the door switches and onto which the door latches lock when you close the door.

The screws on these mounts may be loose. If they get too loose, the switches will not be activated properly.

Sometimes it's a broken tab on the switch holder, allowing the switch to rotate just out of position. This tab can be hard to see, since it is under the bottom edge of the switch.

One test that sometimes helps is to gently lift up (and/or push down) on the door or handle as you try to start it. If it works or tries to work, then it's a door switch mount or door alignment issue.

If you or someone you know decide to look into it, we have critical information on safety, disassembly and door switches at our site, and our link is at our listing here on FixYa:.

You can find an authorized Panasonic servicer here. You can order Panasonic parts here.

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

Posted on Sep 27, 2008

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Troubleshooting Guide


  • Problem: Totally dead oven.
    Possible causes:
    1. No power to outlet (blown fuse or tripped breaker or GFCI).
    2. Blown main fuse - likely due to other problems.
    3. Open thermal protector or thermal fuse.
    4. Defective controller or its power supply.
    5. Clock needs to be set before other functions will operate (some models).

  • Problem: Totally dead oven after repair.
    Possible causes:
    1. Cabinet screws replaced in incorrect location (safety interlock not engaged).
    2. Any number of screwups. :)

  • Problem: No response to any buttons on touchpad.
    Possible causes:
    1. Door is not closed (some models).
    2. You waited to long (open and close door to wake it up).
    3. Controller is confused (pull plug for a minute or two to reset).
    4. Defective interlock switches.
    5. Faulty controller or its power supply.
    6. Touchpad or controller board contaminated by overenthusiastic cleaning.
    7. Defective/damaged touchpad.

  • Problem: Oven runs when door is still open.
    Possible causes:
    1. Damaged interlock assembly.
    2. Cooling fans (only) running due to bad sensor or still warm.

  • Problem: Oven starts on its own as soon as door is closed.
    Possible causes:
    1. Defective triac or relay.
    2. Controller is confused (pull plug for a minute or two to reset).
    3. Defective controller or its power supply.
    4. Touchpad or controller board contaminated by overenthusiastic cleaning.
    5. Defective/damaged touchpad.

  • Problem: Oven works but display is blank.
    Possible causes:
    1. Defective controller or its power supply.
    2. Broken display panel.
    3. Oven needs to be reset (pull plug for a minute or two to reset).

  • Problem: Whacked out controller or incorrect operation.
    Possible causes:
    1. Previous or multipart cook cycle not complete.
    2. Controller is confused (pull plug for a minute or two to reset).
    3. Defective controller or its power supply.
    4. Touchpad or controller board contaminated by overenthusiastic cleaning.
    5. Defective/damaged touchpad.
    6. Defective sensor (particulalry covection/mirowave combos).

  • Problem: Erratic behavior.
    Possible causes:
    1. Previous or multipart cook cycle not complete.
    2. Bad connections in controller or microwave generator.
    3. Faulty relay - primary (or HV side, much less commonly used).
    4. Defective controller or its power supply.
    5. Bad contacts/connections on mechanical timers. Intermittent fuse.
    6. Power surge at start of cook cycle confusing controller.
    7. Microwave (RF) leakage into electronics bay.

  • Problem: Some keys on the touchpad do not function or perform the wrong action.
    Possible causes:
    1. Touchpad or controller board contaminated by overenthusiastic cleaning.
    2. Defective/damaged touchpad.
    3. Controller is confused (pull plug for a minute or two to reset).
    4. Faulty controller.

  • Problem: Microwave oven does not respond to START button.
    Possible causes:
    1. Defective START button.
    2. Faulty interlock switches.
    3. Door is not securely closed.
    4. Faulty controller.
    5. You waited too long - open and close door to wake it up!

  • Problem: No heat but otherwise normal operation.
    Possible causes:
    1. Blown fuse in HV transformer primary circuit or HV fuse (if used).
    2. Bad connections (particularly to magnetron filament).
    3. Open thermal protector or thermal fuse.
    4. Open HV capacitor, HV diode, HV transformer, or magnetron filament.
    5. Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
    6. Defective HV relay (not commonly used).

  • Problem: Timer and light work but no heat, cooling fan, or turntable rotation.
    Possible causes:
    1. Defective (lower) door interlock switch or door not closing fully.
    2. Faulty relay or triac.

  • Problem: Fuse blows when closing or opening door:
    Possible causes:
    1. Defective door interlock switch(s).
    2. Interlock switch knocked out of position.
    3. Misaligned door.

  • Problem: Loud hum and/or burning smell when attempting to cook.
    Possible causes:
    1. Shorted HV diode, magnetron.
    2. Burnt carbonized food in or above oven chamber.
    3. Shorted winding in HV transformer.
    4. Frayed insulation on HV wiring.

  • Problem: Arcing in or above oven chamber.
    Possible causes:
    1. Burnt carbonized food deposits.
    2. Exposed sharp metal edges.

  • Problem: Fuse blows when initiating cook cycle.
    Possible causes:
    1. Defective interlock switches or misaligned door.
    2. Shorted HV capacitor.
    3. Shorted HV diode.
    4. Shorted magnetron (probably won't blow main fuse but HV fuse if used).
    5. Defective triac.
    6. Old age or power surges.
    7. Defective HV transformer.
    8. Short in wiring due to vibration or poor manufacturing.

  • Problem: Fuse blows when microwave shuts off (during or at end of cook cycle).
    Possible causes:
    1. Defective triac (doesn't turn off properly).
    2. Defective relay.
    3. Shorting wires.

  • Problem: Oven heats on high setting regardless of power setting.
    Possible causes:
    1. Faulty primary relay or triac or HV relay (not commonly used).
    2. Faulty controller.

  • Problem: Oven immediately starts to cook when door is closed.
    Possible causes:
    1. Shorted relay or triac.
    2. Faulty controller.

  • Problem: Oven heats but power seems low or erratic.
    Possible causes:
    1. Low line voltage.
    2. Magnetron with low emission.
    3. Faulty controller or set for wrong mode.
    4. Stirrer (or turntable) not working.
    5. Intermittent connections to magnetron filament or elsewhere.
    6. Faulty primary relay or triac or HV relay (not commonly used).

  • Problem: Oven heats but shuts off randomly.
    Possible causes:
    1. Overheating due to blocked air vents or inoperative cooling fan.
    2. Overheating due to bad magnetron.
    3. Bad connections in controller or microwave generator.
    4. Faulty interlock switch or marginal door alignment.
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    6. Overheating due to extremely high line voltage.
    7. Stuck stirrer fan resulting hot spots detected by sensors.

  • Problem: Oven makes (possibly erratic) buzzing noise when heating.
    Possible causes:
    1. Fan blades hitting support or shroud.
    2. Vibrating sheet metal.
    3. Vibrating transformer laminations.
    4. Turntable or stirrer hitting some debris.

  • Problem: Oven light does not work.
    Possible causes:
    1. Burnt out bulb :-).
    2. Bad connections.

  • Problem: Fans or turntables that do not work.
    Possible causes:
    1. Gummed up lubrication or bad motor bearing(s).
    2. Loose or broken belt.
    3. Bad motor.
    4. Bad thermostat.
    5. Bad connections.

on Mar 30, 2008 | Kenmore 80412 Microwave Oven

1 Answer

Panasonic Invertr NN-S963, no heat and shuts off approx 7 sec. before end time. Fan works. Is it magnetron? If so, approx. how much to fix?


Magnatron failure is rare. I suggest you check your door interlock safety switch. Do you regularly open the door while the machine is running? I did and I found out that the micro switches (door safety swwitch) are just not up to that kind of abuse. Your maching thinks the door is open because the contacts are burned to the point they do not close.

Unplug the machine, DO NOT TOUCH THE SILVER CAN! You will find the switches opposite the hinge. Check them with a volt ohm meter on contunity setting.

You cam probably get replacement switches at a electronics parts place.

There are other things that can be wrong but you should check these switches first. Cost should be less than $10.00 if you do it.

Let me know if this works for you.

a

Sep 21, 2009 | Panasonic NN-S963BF Microwave Oven

1 Answer

Panasonic - NN-T993SF 1350 watts microwave


Sorry this is something you wont fix at home I couldent even do this one.This is a nice unit depending on the cost this one I think is worth the repair bill , Good luck DFD please rate me TK U

Apr 12, 2009 | Panasonic NN-T993SF Microwave Oven

1 Answer

Panasonic Microwave Model #NN-T993 displays fine and when I push the start button, the display shows it should be working, but turntable is not turning and is not heating.


Sorry to tell you this but some ones has to. Your unit is shot. the cost of repair out weights the cost of a new one. you can get a basic unitn 800 wates for a bout 89.00 you cant repair for that. Try looking at Thrift store;s you can find good clean working microwaves for $25.00 or less no kidding. happy hunting DFD

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1 Answer

Dacor dcm24s.light, fan, and control panel work but turntable and heat do not


Most likely the bottom door switch. Dacor units are built by Sharp and that switch is a very common problem. You'd either need to check the switch with an ohm meter or remove the cover of the switch to see if it's burned inside.

Oct 20, 2008 | Sharp R-930AK Convection/Microwave Oven

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My first guess would be to checvk the venealation fan

Mar 31, 2008 | Panasonic NN-T993SF Microwave Oven

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I have the same problem starting yesterday April 19. Have you gotten any answers.

Mar 12, 2008 | Panasonic NN-T993SF Microwave Oven

1 Answer

Panasonic Microwave Turn table rotates when door is open


Found this Panasonic post in the Samsung section!

If it moves just a tiny bit when the door opens and then stops, that's normal.

If it keeps running when the door is open, that's usually due to a bad door switch or broken / loose door switch mount.

If you or a friend decide to look into it, we have critical safety information, info on door switch diagnosis and replacement, and
disassembly information at our site, linked here on Fixya: http://tinyurl.com/yzjozk

Any Panasonic parts not available locally can be had here: http://www.pasc.panasonic.com/epartr

We appreciate your thoughtful rating of our answer.

Nov 03, 2007 | Samsung SMH7159 Microwave Oven

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