Microwave fuse keeps blowing

I was unable to locate a service repair manual specific to your microwave; sorry.

You'll must likely have to find a Sharp service and repair center.
I've attached a link that contains the user's manual to your microwave...it has the phone number and address of Sharp; perhaps you can phone them and ask where a repair center is located.

This is the diagnostic check list Sharp recommends before calling for service:
SERVICE CALL CHECK
Please check the following before calling for service:
1. Does the display light up?
2. When the door is opened, does the oven lamp come on?
3. Place one cup of water (approx. 250 ml) in a glass measure in the oven and close the door securely. Oven
lamp should go off if door is closed properly. Press the INSTANT COOK/START pad once.
A. Does the oven lamp come on?
B. Does the cooling fan work?
(Put your hand over the rear ventilation openings.)
C. Does the turntable rotate?
(The turntable can rotate clockwise or counterclockwise. This is quite normal.)
D. After one minute, did an audible signal sound and COOK
indicator go off?
E. Is the water inside the oven hot?
If "NO" is the answer to any of the above questions, please check your wall socket and the fuse in your meter box.
If both the wall socket and the fuse are functioning properly, CONTACT YOUR NEAREST SERVICE CENTRE
APPROVED BY SHARP.

Sharp Carousel 395Y Operation Manual And Cookbook

Most likely the cavity temp fuse is open. Sharp mounts theirs typically near the back of the unit, on the top center.

The service manual is here:
http://www.microwavedisplay.com/r820bc_bk_bw_sm.pdf

You can get Sharp parts from Encompass here.

If it went dead almost immediately after pressing the Start pad, that's usually a shorted high-voltage capacitor.
See http://www.microtechfactoryservice.com/cap_test.html

If it went dead several seconds after pressing the Start pad, that's usually a failing high-voltage transformer.
See: http://www.microtechfactoryservice.com/xformer.html

If it goes dead or blows the breaker (or GFI) when you plug it in or open or close the door, then there's a problem with a door switch or door switch mount.
See this: http://031d26d.namesecurehost.com/mwd/doorsw.txt

Maybe... Did you check the high voltage diode?... A shorted diode keeps the fuse blown... Ty

If the 20A fuse is blowing, it is often the high voltage transformer or magnetron. If this is the case, and the microwave is not under warranty, replace it. Residential microwaves are generally considered disposable. Parts and labor are just too expensive. A magntron or transformer can cost more that half the cost of a new microwave.

I don't know of a reset button but there is a fuse that you have to remove the outer cover to get to that has a habit of blowing

i just checked my R-3A36 manual to find out the wattage. it's 800 watts. i make pralines in my microwave. i am always asked for the recipe. so i needed to be able to tell people the wattage of my oven so they can adjust the recipe to their oven.
garry, metairie,la.

Is it totally dead? No display? Or just does not cook? If it made an unusual noise before it 'died' something probably shorted out.... You need an ohm meter to troubleshoot. If the fuse is open, switches and HV circuit need to be checked before replacing fuse. Sometimes on the convection Microwaves (not just Sharp) the fuse will 'rust' and open rather than blow. Or the fuse holder can over heat and fail.

I too believe that a "protection fuse" was possibly blown. It would need to be found and get replaced. Hopefully it is just a fuse and nothing else because the way it sounds to me, the microwave may be damaged.

Good Luck!