Question about Panasonic NN-T888S Convection/Microwave Oven

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No power. I changed fuse but microwave blows it immediately.

Unit stopped working completely. Not even the clock. I found a 15amp 125v fuse inside the cabinet (right rear) Replaced that and bake/broil works fine, but microwave blows the fuse immediately. Any thoughts? This unit has only had about five hours of use total, but is three years old.

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Be very careful! Standard microwaves have 2100volt capacitors and commercial ones 4000 volt capacitors.
*Decharge your capacitor(s) before doing diagnostics*.
You are now testing the high voltage side (as it works on convection). The main components are a transformer, a capacitor, a diode and a magnetron (havent seen a triac in a panasonic residential). If you have a proper meter that can test uf, decharge the capacitor, then test the capacitor, if it reads 0, you need a new capacitor (10$ used typically, 14$ new from ebay). To test the magnetron, decharge the capacitor first, remove the spade connections, test each leg to the frame of the microwave... if it shows measurable resistance, the magnetron is bad. The transformer is not something you test as I personally dont have a 4000 volt meter. If the diode, the magnetron and capacitor are okay, then the transformer is bad. To eliminate any other function, disconnect the low voltage to the transformer run a micropower cycle and check the fuse.
Hope that helps. My first instinct is the capacitor.

Posted on Dec 19, 2009

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i had the same problem and did what this fella suggested and worked just fine. 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. If the model number you listed this question under is correct, the line fuse is connected in line with the power cord inside the unit and is listed as part of item 4 in the parts listing (part number STD384200).

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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.


Replacement parts can be ordered at any of the following websites:

searspartsdirect.com
pcappliancerepair.com
appliancepartspros.com
repairclinic.com

All these sites are reputable and offer competitive pricing, so shop and compare. The first three sites on the list also inlcude exploded view parts illustrations to assist you with locating and properly identifying any parts you may need.


If the model number you listed this question under is correct, the line fuse is connected on the wiring harness inside the unit and is listed as part of item 14 under the "Interior" parts listing (part number 815174). There is also a Thermal Cut-Out (TCO) in the High Voltage network mounted on the magnetron that, if blown, will cause the same symptoms. It is listed as item 15 under the "Magnetron and Air Flow" parts listing. The part number is 815076.

CAUTION: DO NOT under any circumstances attempt to operate or troublehsoot the microwave oven with the exterior case removed. Voltage potentials in the High Voltage network can exceed 3,000 volts. Always UNPLUG the unit when attempting any repairs.


If the line fuse is blown, you can usually purchase a box of fuses at a hardware store for less 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.

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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. If the model number you listed this question under is correct, the line fuse is connected in line with the power cord inside the unit and is listed as part of item 4 in the parts listing (part number STD384200).

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