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Joined: 11/2/2009(UTC)
Posts: 176
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Normally i just browse appliance problems and post my opinion of whats wrong but i never worked on microwaves so i'm posting a problem of my own. i have a Sharp carousel over the oven microwave that will not heat at all. the only additional info i have is that i think a power surge may have damaged it because the control panel doesnt display correctly (looks like chinese lettering) The microwave will start and count down the seconds and everything but just will not heat. ANY advice would be greatly appreciated even if your not too sure. i was thinking possible bad diode but im really just guessing here. oh yeah, on a side note i swear i saw a spark or lightning bolt or SOMETHING when i started it (inside the microwave) so i'm not too eager to just break it open and try to test stuff without some guidance first. I am very good with appliances so any advice would be great
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Rank: Member
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Joined: 3/28/2009(UTC)
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I rarely work on sharp microwaves but it sounds like the control. What you will have to do is find out if voltage is getting to the transformer while the microwave is running. The easiest way I have found to do this is to find the relay on the board that sends power to the transformer (you will have to look at the wiring diagram) close the door and check voltage across it. You should get 110V then start the microwave and the voltage should drop out because the relay closed. If this happens you can be reasonably sure there is voltage going to the transformer. Note that the test above will not rule out the magnetron cut out switch you would have to test voltage right at the transformer to rule that out or test ohms across it. Be careful the other side of that transformer is very high voltage you don’t what to get hit by that trusts me! Not to mention you will destroy your meter if you test the wrong side.If the voltage doesn’t drop out when you turn the microwave on the relay isn’t closing and the board is bad (possibly a bad solder joint). If the voltage does drop out you may need to test directly at the transformer. If you don’t have voltage at the relay I would think the control is bad because it sill counts down and all so you wouldn’t think the door switches would come into play. But you will have to look at the diagram to confirm. If you do get voltage to the transformer you have a problem with the high voltage side such as a bad diode, capacitor, transformer, or magnetron tube. Hope this helps!Microwave Repair Guide
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Rank: Member
Groups: Registered
Joined: 11/2/2009(UTC)
Posts: 176
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I appreciate the replies and advice and i'll dive into this thing soon - have a lot going on right now so it might take me a little bit but i'll post any problems or questions i mite have when i tackle it. thanks again for the quick replies and advice!
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Rank: Member
Groups: Registered
Joined: 11/2/2009(UTC)
Posts: 176
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ok i finally got around to opening it up.. the diode is all black (possibly from blowing out?) and has continuity (i removed one wire to test but will double check with both wires removed). i then reversed the positioning of my meter terminals and tested again and it showed continuity on the flip side also. i've seen a few diodes before and they have always been a small clear tube but mine was black (possibly from burning). would this mean the diode is bad?
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Rank: Member
Groups: Registered
Joined: 3/28/2009(UTC)
Posts: 1,648
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Well a lot of them are black anyways but if you have continuity both ways it is bad. It should be open one way and a very high ohm reading the other.
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