• ** REMEMBER! **The microwave can still shock you even unplugged!!

    ALWAYS discharge the high-voltage capacitor first if you even think your hands will come close to any HIGH VOLTAGE components.

    Jeff mentions this: Anything in the high voltage ( magnetron, capacitor, diode, wires to and from ):
    ...Use a metal ( not the shiny chrome type ) screw driver with a insulated handle to short across ( touch both at the same time ) the terminals of the high voltage capacitor to discharge it.

    From Jeff's site: http://www.applianceaid.com/component-testing.php

    Jake
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R305HK Sharp Microwave - New capacitor, new magnetron, sharp carousel still blows internal fuse

Deplorable

Premium Member
Joined
Jan 13, 2021
Messages
7
Location
Ocala fl
Model Number
R305HK
Brand
Sharp
Age
More than 10 years
OK, so this is an old microwave...been a good one and I want to keep it. Context: cooking a dish that required some length, 20 minutes, I believe, the micro made a loud rumble after 15 min or so and blew the internal fuse.
Replaced the fuse...it made the rumble for 2-3 second, then blew the fuse again. Checked the capacitor...it was shorted. Replaced it with identical cap---2200VAC .94UF. Same thing. Hit start and the fuse (20amp 250 volt) blows...power transformer seems to check out...no shorts to case...ohm meter set to 200 ohms gives me 1.6-1.7 on the secondary terminals, 00.9 on the primary terminals, 97.7 on the high voltage single tab.

Monitor switch shows no continuity when the tang is depressed...and some crazy readings when it is depressed...numbers jump all over the display won't settle...seems apparent the monitor switch - d3v1g2c25 -
is not good, but I would like an learned opinion...thanks...
 

Dan O.

Appliance Tech
Staff member
Joined
Oct 9, 2004
Messages
4,259
Location
Ontario, Canada
The monitor switch has to be functioning properly or it will blow the fuse if trying to heat, as a safety precaution. If it stopped making proper contact while cooking, it would cause the fuse to blow.

Whether that's your only problem, I have no idea.

Dan O.
 

Deplorable

Premium Member
Joined
Jan 13, 2021
Messages
7
Location
Ocala fl
Thanks, Dan. I have ordered a new monitor switch. However, I believe the transformer is the issue.. The single high voltage lead that connects to the capacitor indicates that it is shorted to the case and anything else it touches on the chassis that is metal...not sure how I missed this the first time around. I should have noticed when I was 'discharging' the new capacitor...it seemed dead with no arc or 'spit' when I shorted the leads.

Curious though...the old capacitor was definitely shorted...can a shorted transformer cook the cap or is it the reverse...? Or just coincidence? Thanks for sharing your knowledge.
 

Deplorable

Premium Member
Joined
Jan 13, 2021
Messages
7
Location
Ocala fl
Please humor me with one more question. I ordered the original transformer--TAR220ATT A705WRXX-- for the Model R305HK--but I have little faith in the supplier. I notice there is a similar transformer available--TAR220AT A700WRXX--for the Model 315HK. I haven't found a source for Sharp Transformer specs...but I do know the model 315HK advertises 1200 watts while my 305 is 11. Curious if the A700WRXX would be ok? Both models operate at the same freq 2450.
 

Deplorable

Premium Member
Joined
Jan 13, 2021
Messages
7
Location
Ocala fl
I think I just answered my own question. The sharp magnetron for my 305HK is different than the 315HK...damn
 

Dan O.

Appliance Tech
Staff member
Joined
Oct 9, 2004
Messages
4,259
Location
Ontario, Canada
Im afraid I don't know the specs for either of those components or models. i don't have access to Sharp technical information.


Dan O.
 

Deplorable

Premium Member
Joined
Jan 13, 2021
Messages
7
Location
Ocala fl
Saga continues. If two different sharp microwave ovens use the same identical magnetron, then would one transformer from one work OK for the other?
 

Deplorable

Premium Member
Joined
Jan 13, 2021
Messages
7
Location
Ocala fl
It seems logical that if magnetron A uses power transformer B in one application...all other things being equal- Capacitor, diode, etc..then transformer B should work with any magnetron A...if you read of someone in Florida being cooked, you will know I was wrong.
 

Deplorable

Premium Member
Joined
Jan 13, 2021
Messages
7
Location
Ocala fl
Well, WTH? Replaced the magnetron, replaced capacitor, replaced the power supply, replaced the monitor switch...hit start and it blows the fuse.
Remove the diode from the circuit and everything runs...but of course, no heat. Refuse to give up. New diode on the way.
 

Dan O.

Appliance Tech
Staff member
Joined
Oct 9, 2004
Messages
4,259
Location
Ontario, Canada
It the fuse blows immediately as soon as turned on to cook, often one (or more) of the door switches may not be activating properly. It doesn't necessarily have to be a defective switch but could be a loose or worn switch holder too.

BTW. Whenever a fuse blows, most manufactures suggest replacing the monitor switch at the same time as too much current will will have passed through its contacts and often damages it.

I'm afraid I do not have any other suggestions. Sorry.

Dan O.
 
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