Question about Sharp Microwave Ovens

7 Answers

My Sharp R-9h91b microwave oven stopped working. The LED panel does not light. I checked the fuse in the microwave and it seems OK. AC current comes into the plug in the back, but seems to stop before it gets to the fuse. Any idea of what to do now?

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  • richardbw0 Sep 28, 2008

    There seems to be at least two fuses in this microwave, according to the schematic in the interior metal covering. The fuse that is obvious, a grey, cylindrical, 15 amp fast-acting ceramic 1/4" X 1-1/4", is OK. There seems to another fuse called a thermal fuse on the schematic that I can't seem to locate. Do you have any diagrams about where this fuse is and how to replace it, or must it be replaced by a professional technician?

  • richardbw0 Sep 28, 2008

    I have determined with a multimeter that the current is coming through the plug into the microwave, but not getting to the 15 amp ceramic fuse noted above. Following the wires is difficult without a photo or more detailed schematic.

  • richardbw0 Sep 28, 2008

    I don't think the connection between the fuse and the where the plug enters the microwave is cut. I think the "thermal fuse" may be blown, but I can't seem to locate it. And, a prior person who posted said that the "thermal fuse" should be changed by a professional technician. Is this correct?

  • richardbw0 Sep 29, 2008

    MicrowaveSvc posting was helpful, especially including the Sharp service manual for the microwave. However, when I went to the manual I determined that Procedures H, I and J to check the monitor fuse, the magnetron temp fuse, and the thermal cut-out were what I needed to do, and none of those procedures were explained in the manual. Do you have those procedures from Sharp?

  • richardbw0 Sep 29, 2008

    I've seen several responses to my question that seem to have disappeared. Any idea where they are? I want to contact MicowaveSvc who responded to my question to get a PDF of the base service manual which probably has the solution to my problem, but his reply seems to have disappeared from my posting.

  • richardbw0 Sep 29, 2008

    Can I get some help here? There is no response to my last two posts, although I get emails saying there are new responses. I don't understand.

    Thank you.

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7 Answers

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  • Expert
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I am going to help you the best way I can. This unit does not have a lot of support from Sharp and the aftermarket any longer. Parts are really not available asnd are costly. The fuses cost $10.00 each and the magnitron is $100.00. For those prices, you could get a new, state of the art unit and not have to worry about an issue, that is being caused by some other issue and is bound to cost you more than the unit is worth.

I normally would not recommend this, but truthfully, it is the best solution and the safest. This is a microwave and already by invading the chassis exposure to radiation has increased. Just my two cents.

Posted on Sep 29, 2008

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  • Master
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The thermal fuse is located inside in the transformer,in the secondary windings,just tear the wrapping tape,it is a white cylindrical shape,it like an asbestos material made,and check if it open.

Hope it may help you;

Regards,
VOTIT

Posted on Sep 29, 2008

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  • Master
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The thermal fuse is normally located inside the power transformer. You can check the transformer with a multimeter. First, and most important, UNPLUG THE MICROWAVE from the wall. Then with your multimeter check the transformer by setting it to resistance and see if you have continuity across the primary and the secondary. If either of those are open you have found your problem. The transformer should be very close to zero ohms. The transformer has a pair of wires going into it on each side. One pair is the primary and the other is the secondary. Unplug those wires from the board before you check them. If the connector has 3 wires on it that is the secondary and you need to check the continuity across the 2 wires of the same color.

If you still want more help from me, let me know by addressing your post
to me i.e. @tech48. Or you can request help from any other specific expert by addressing your post to them directly the same way.

If you accept my solution I will continue to help you with part numbers and any other help you may need. But I think that your power transformer is open and replaceing it should solve your problem, but lets first make sure it is the transformer that is bad.

Dave

Posted on Sep 28, 2008

  • 1 more comment 
  • Dave DeGain
    Dave DeGain Sep 29, 2008

    I just checked out the schematic for your microwave and it has two secondaries on the power transformer. It also looks like, from the diagram I have, that the transformer may just plug right into the board with no wires coming off of it. It is hard to tell from the diagram I have, it is not a picture, but the board diagram makes me think that the transformer plugs into the board with leads that go thru the board and get soldered on the bottom. If you remove the board that the transformer is on you can check the transformer. One side looks like it has 2 leads for the primary and the other half of the transformer has two separate secondaries with two leads each. When you check all of these leads for the transformer you need to check them in pairs. One pair at a time. Those must be checked by putting your meter probes on the right leads at the same time. The diagram shows them listed by numbers. If they are numbered on the board you need to check numbers 4 and 5 at the same time, then check numbers 7 and 8 at the same time. The primary shows it being numbered 1 and 3. There may be extra holes in the board that do not have leads going thru them.

    3 1

    8 7 5 4

    Above is the way they should be laid out on the board if this turns out the way I have typed them. The transformer does not have the thermal fuse in it, I should have looked at the schematic first, sorry about that. But it is still a good possibility that the transformer is bad. The schematic does show that there is a magnetron temp fuse in series with the other fuse and one side of the power plug that goes into the wall. You can check the continuity by putting one probe on the fuse you have checked and the other probe on one side of the plug. If you get no continuity on that side of the plug, check the other side of the plug. One side should have continuity all the way to the fuse you checked already. Please be sure to have the microwave unplugged all the time you are checking it, even before you take the top off the unit.

    Let me know if I can be of further help.

    Dave

  • Dave DeGain
    Dave DeGain Sep 29, 2008

    I am sorry, after reading your question more closely without all the distractions I have going on in my house the last hour, I think I have figure out your problem. You said the you are not getting voltage to your fuse. This can only be one of two things, either the "magnetron temp fuse" or the "oven thermal cut out". You must determain which it is, and then replace it. They should both have near zero ohms across them where the connect into the board. They connect into the board between the fuse and the power cord. The "oven thermal cut out" shows it having pink and black wires going to it and the "magnetron temp fuse" has black and red wires going to it. Check the continuity from the pink to the black and then check the black to the red wires. They should both be near zero ohms.

    The part number for the magnetron temp fuse is "QFS-TA013WREO"
    The part number for the oven thermal cut out is "RTHM-A024WREO"

    It is still possible that the reason one of these parts has failed is another bad component. The magnetron temp fuse could have gone bad because the magnetron is bad.

  • Dave DeGain
    Dave DeGain Sep 29, 2008

    If you are able to read this post, your best bet is to contact MicrowaveSvc directly if you have not been able to see his many posts to help you. You can click the link with his username or make a post addressing him directly I.E. @MicrowaveSvc and he will know that you want to communicate with you.



    He has given you the best solutions to your problem so far and seems to have hands on experience repairing your product, and you have conversed with him already. I believe he has posted the best soutions to your problem and if you rate any post from him as a "FixYa!" I feel certain that he will continue to give you whatever help you may still need.

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  • Sharp Master
  • 9,011 Answers

We have the service manual for this model and have uploaded it to our site here to help you. You will need the free Acrobat Reader to view or print it.

A microwave can be dead for many reasons.

It may be the fuse, which is usually located behind the grille or on the floor of the oven behind the control panel or between the door switches.

If the fuse is good, it may be an open thermostat or thermal cutout (TCO) / thermal fuse on or near the magnetron or on top of the cavity / body of the oven.

If it goes dead for a while during or after cooking then comes back on, the magnetron is probably overheating and causing the magnetron thermostat to open.

Then when it cools, it closes the circuit and allows power through again.

When checking TCOs or thermostats, if it has a hood fan thermostat, that should read open, as opposed to the others, which should read closed.

The TCOs you need to be concerned usually with have all black or white wires only. Please reply with photos of your interior if you have questions.

If it went dead almost immediately after pressing the Start pad, that's usually a shorted high-voltage capacitor.

If it went dead a few seconds after pressing the Start pad, that's usually a failing high-voltage transformer.

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.

If it's intermittent or random, it may be a bad connection, usually on the control board or a loose fuse holder, or even an intermittent fuse.

You should do a continuity test on the fuse while it's in the holder (with the microwave unplugged, of course) then turn the fuse by hand or take it out and put it back in, then test it again.

If you remove the fuse, then press the meter leads against the ends, it can allow internal contact to be made and make a bad fuse appear to be good.

The best place to order Sharp parts is Tritronics.

In some cases, there may have been an electrical spike which activated the built-in surge protection. This can require repair of the circuit board, which we do nationwide for $39.95 in most cases in about a week or so.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

William E. Miller
prototech@usa.net
http://www.microwavedisplay.com

Posted on Sep 28, 2008

  • William Miller
    William Miller Sep 29, 2008


    Hi, I'm the guy who gave who the service manual link and the long, very detailed answer that covered just about everything that can make a microwave "dead".

    You don't actually need the base service manual since this manual has everything you need to locate the parts and the part numbers, as well as the overall schematic.

    The magnetron temperature fuse (ref # 1-7, original part # QFS-TA013WRE0) is located in section 3-D of the exploded view on page 25. Physically, it is clipped onto the waveguide above the magnetron and it looks like the right item in the attached drawing.

    The oven thermal cutout (TCO) (ref # 1-8, original part # RTHM-A024WRE0) is located in section 2-H of the exploded view on page 25. Physically, it is located on the left side of the chassis near the convection fan assembly and it looks like the left item in the attached drawing.

    The best place to order whichever of these you might need is parts is Tritronics. If the part numbers have changed, that will show up on their Web site.

    The testing of these parts is simple continuity testing: With your meter on the ohms scale (and oven power unplugged of course) measure the resistance at the terminals of the thermal cutout (TCO). It should read virtually zero. If it reads high / infinity, then it's open and needs to be replaced.

    You can also place a jumper or clip lead across the bad (or suspected) device and plug the oven in just long enough to see if it comes to life. Do not cook with the jumper in place, and unplug it right away, avoiding contact with any inside wires or connections.

    The schematic on page 4 shows you the "order", if you will, in which the current flows. (Yes, I know it's AC). From the plug, it goes through the oven thermal cutout, then the magnetron temperatuere fuse, then the line fuse.

    On that schematic, the very bold black lines show you the essential path required to get power to the board's low voltage transformer, which should result in a lit display assuming the boar dis okay.

    If you need more help, please feel free to write me at prototech@usa.net.

    If this is not a FixYa, I don't know what is! *grin*

    We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

  • William Miller
    William Miller Sep 29, 2008


    Here is a drawing to show you what microwave thermal cutouts / thermal fuses look like.

    Holy cow!!! Please don't tear apart your transformers - that's not where they are in a microwave!

    We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.





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The continuity of current is lost you need to check the continuity by multimeter .Then we can get idea what causes the problem ?


SAM ANDERSON

Posted on Sep 28, 2008

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  • Master
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F your microwave oven doesn't seem to work at all, check these:
Fuses Usually, when your microwave oven doesn't work it all, the internal fuse (thermal fuse) is blown. This fuse protects both you and the oven. When it blows, you need to have a qualified appliance repair technician replace it.

Door switch If the fuse isn't the problem, check the door hooks and the door-release button. When these are broken, the door switch doesn't activate, so the oven can't work.

Posted on Sep 28, 2008

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  • Sharp Master
  • 13,433 Answers

Lets start with


It doesn't work at all If your microwave oven doesn't seem to work at all, check these:

Fuses
Door switch
Fuses Usually, when your microwave oven doesn't work it all, the internal fuse (thermal fuse) is blown. This fuse protects both you and the oven. When it blows, you need to have a qualified appliance repair technician replace it.

Door switch If the fuse isn't the problem, check the door hooks and the door-release button. When these are broken, the door switch doesn't activate, so the oven can't work.

Posted on Sep 28, 2008

  • 1 more comment 
  • Ekse Sep 28, 2008

    If the connection between the connector and the fuse is cut, then you need to troubleshoot what is wrong in the middle, if the connection is cut you need to fix it, I suppose you know how? Wire from point A to point B, but if there is something else on the middle, and I haven't seen the scematics, then check the components in the middle.

  • Ekse Sep 28, 2008

    Also, when working inside any electronic device, always unplug.

  • Ekse Sep 28, 2008

    Yes thats correct, as I said it also. you need to have a qualified appliance repair technician replace it.

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IrishDruid
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SOURCE: Sharp R-9h91B microwave oven stopped working

If the fuse isn't the problem, check the door hooks and the door-release button. When these are broken, the door switch doesn't activate, so the oven can't work.

Posted on Sep 29, 2008

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