I think the fuse is blown on my emerson microwave mw8781sb i test the power coming from the plug and there is power but none after that

Screws are probably on the bottom of the microwave - then the whole side and top come off - then you have access to the back - i doubt it has an internal fuse though! I presume you have checked the plug fuse.

Be very careful - microwaves generate a massive electrical output and will fry you in a second!

First check is the main fuse of the unit. On countertop units, you will need to take the shell off. The fuse will be close to where the cord comes through into the unit. OTR units, this main fuse is usually behind the control panel or possibly behind the vent. Usually the fuse is obvious if blown, otherwise test with an OHM meter, if open, replace fuse.
Some brands will also have a thermal cut-off fuse in the incoming voltage line to the control board. Older Maytags and Samsungs have this fuse in it. This thermostat looking fuse is usually above the oven cavity somewhere under the outside shell. Sometimes you can get to it through the vent of OTR models. Test with an OHM meter, replace if open. Use the VOM
God bless you

Make sure that the program controller is working if not check power - step down supply, the pads are responding- if not faulty pads- or the door switches, if the switch contact are not good then it will not trigger the processor to switch on the waveguides. If the lights or fan work without any display or action of program being triggered to start then it can be a possible fault on the main board or the processor. Sometimes insect secretion can short the board and display panel and so the processor can work in such an erratic manner. If so clean, solder and reset the board. Now identify the parts by clicking this link: http://www.espares.co.uk/advice/microwave/a/5/141/identifying-microwave-parts.html

If there is no heating please do not switch on unless you have confirmed the fault. It is possible that the Magnetron is faulty, the temperature cut off is faulty or the main capacitor is short. It is also quite possible that insect can get into the oven and create soft spots. When you switch on these will create a short and make the voltage jump and in the long run damage the magnetron. Check this link to know how a microwave works:

http://www.espares.co.uk/advice/microwave/a/5/1443/how-a-microwave-oven-works.html

So Remove cover after disconnecting , check for dirt/moisture in the cabin, if so wipe clean and dry, check the magnetron and area clean and use an jet air to clean off. Check the wave guide covers, if food had deposited
then it must be checked or replaced. See link: http://www.espares.co.uk/advice/microwave/a/5/1146/how-to-replace-a-microwave-guide-cover.html

You can get parts on the link below.

http://www.partstore.com/Model/Funai+Corporation+Inc/Emerson/MW8781SB.aspx

It probably requires a magnetron and/or diode pack.

Most of the manufactory has put them in the back where the power cord comes in.

You have a shorted high voltage capacitor.

Here is a link you or someone you know can use to test it, but please read the safety info:
http://www.gallawa.com/microtech/cap_test.html

For more help from Emerson visit here or get help using your appliance at 1-800-898-9020. Get help locating a servicer or parts at 1-800-695-0098.

Emerson parts are distributed by Fox International and their number is 800-321-6993. Or you might try e-mailing [email protected]

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I have replaced the main fuse on this model. Though blown main fuses are common in this model, it will not even turn on when they blow, so your problem is most likely NOT a blown fuse. I had heard of your problem so, when replacing the main fuse inside one, I looked for additional fuses and saw none. The store was wrong. Even if it were a fuse, the security Torx screws mean that you couldn't replace the fuse anyway.

This microwave seems to have been haphazarly been recommended by Consumer Reports, but it is terribly unreliable. The turntables break when popping popcorn, the main fuse repeatedly blows, and they also stop heating.