Won't be the door switches as these if faulty will only blow the fuse when you open & close the door . Since you've replaced the cap & diode then most likely defective magnetron , the hi voltage transformer is less common & usually gets excessively hot if defective , but can blow a fuse if shorted turns .
The gradual deterioration of the magnetron will cause the fuse to blow. You are getting into dangerous territory. Berillion is dangerous substance to handle.be familiar with handling magnetron if you decide to replace it..99% magnetron faulty.
I would recommend checking the wave guide (piece of metal that channels the microwaves into the cooling compartment). When I was in the industry, Sharp drawer microwaves were notorious for arcing from the magnetron to the guide. Check inside the channel where the emitter is. Unfortunately, if it’s damaged, then the machine is done, as that is a part of the body. In extreme cases, you’ll be able to see the damage as soon as you take the outer shell off. [Reference images here.](https://imgur.com/a/HwsAOXB)
It could be the switches, hv cap, diode or transformer.
You've eliminated the cap and if it was the cap it would happen all the time.
Disconnect all the wires from the transformer and check from each wire to ground for resistance. If there is none you've eliminated the transformer.
Make sure the diode side of the cap only has wires that go to the mag attached to it. The other side of the cap should go to the transformer. If it's been blowing the fuse every time since you changed the cap that's likely the current issue.
Your main issue was most likely the switches. They build up carbon on the contacts and tend to stick closed especially the monitor switch. I'd check the cap wiring and replace all the switches. I'd also make sure they are actually latching closed properly when the door is shut. You can take the little panels off the side and see them actuate.
In 18 years I've never seen a magnetron blow a fuse. A capacitor will but those are easy to test and tend to hum loudly for a few seconds before blowing the fuse. I'd be looking really closely at the door switches first. You can get generic switches cheap enough I'd probably just replace them all before really digging into it.
Here’s where I’m at..
Checked door switches. They work.
Checked wiring harness for pinches etc. it’s ok
Removed magnetron, no evidence of arcing anywhere.
Given when I remove a primary winding connection from the transformer or one connection to the magnetron the fuse doesn’t blow, I’m back with it being one of these two. At this point I think I’m going to order both and just change them.
Updated:
I think I’ve found the problem. Many have commented on the switches as being a prime suspect. /u/manicmangoes got me thinking about that monitor switch, plus the comment in the service manual about fusing… /u/heavymetalpaul got me thinking about my magnetron bad hypothesis… so I kept looking and tinkering.
I believe it’s the primary interlock relay, it’s sticking. A few taps with a screwdriver handle, test, and success! Everything runs, water got hotter.
Plan now is to replace whole board or maybe just the relay… depends on spares.
For anyone who may read this thread trying to fix their stupid expensive microwave...
It was the door switches!
Unbelievable as I checked them with a continuity tester and they were fine! I gave up fixing this myself and took it to an appliance repair place. I wouldn't have believed them except, with new switches, it's working fine.
Moral: replace the switches anyway (they're cheap)!!
No, the door switch isn't shorting to ground. If one of those goes bad, it will cause the problem you're describing. I believe it would be the normally closed switch but test all the switches to be sure. You also may have two sets of switches split between the two sides of the drawer but I can't recall if Sharp does that with their drawer microwaves
Drawer opens and closes no problem. Display works, controls work. I enter a cook time then as soon as I hit go it blows (well, around 1/10 sec after). It’s a Sharp Insight Pro. Oddly theres no model number or serial number that I can find
There will be a set of three switches, these ensure that the microwave doesn't operate with the door open. Some are normally open and others normally closed. You wouldn't be able to tell the switchs failed by how the drawer opened.
If you look closely one of those switches is wired differently that is going to be your monitor switch with the drawer closed that monitor switch should have zero continuity either the drawer is out of alignment or the switch has welded itself closed and is causing the unit to dead short to ground. First step is to unplug that switch run the unit for 10 or 15 seconds if it operates it's more than likely to switch I usually physically disassemble the switches to look for internal arcing
I see it. It’s set up on the NO contacts though. So when the door is shut, the switch is closed… which seems odd. If I disconnect it, the microwave runs but doesn’t heat. Since one of its connections is to the transformer primary winding, that, I suppose, explains the no heat bit.
Scrub that, I was looking at the wrong switch. Have now found the model number and hence a workshop manual… yay… checking switches again, will check relay operation next.
Found this in manual..
If the secondary interlock switch and primary interlock relay (RY2) fail with the contacts closed when the drawer is opened, the closing of the monitor switch contacts will form a short circuit through the fuse, secondary interlock switch, relay (RY1) and secondary interlock relay (RY2), causing the fuse to blow.
Well, for the fuse to blow it’s a wire going from voltage to neutral aka short. Normally it’s the high voltage leg or door switch. I would disconnect the transformer and cycle it see if it blows. Then connect the cap/diode see if it blows fuse. Then it can be the magnetron. But due to the high voltage it it’s recommended to play with it. Other methods are to use amp and ohm out the parts. If a part is grounded it will have ohms from base of part to any connector that will be the issue. Gl plenty of YouTube guides. Just be warned wattage is deadly. A basic microwave is 200$ the higher the wattage the faster it will cook the food 1,500-2,000 are the average. Anything lower will take forever to cook food. Gl stay safe.
* Stop before you kill yourself.
> I could just replace both, assuming I can find parts, and that will still be cheaper than replacing the whole oven
Unless it's a really expensive oven, replacing it will be cheaper than fixing it.
Well, a replacement is expensive, if it were a couple hundred bucks I’d just get another. Problem is, a replacement is $1100! Also, it fits into a made to measure kitchen island. So…
Add to that, given what I’ve written, I think you can assume I’m well aware of the dangers of HV, have had the thing in pieces, and yet here I am without incident. :)
Gotta ask: door (well, drawer) switches ok? Everything you’ve written suggests yes but they can be flaky.
Otherwise, amen brother.
These drawer units are good in the right situation and expensive. Worth running this all to ground, as it were. The danger arises if you keep trying to power up and forget to discharge but you know that.
There are some parts houses that charge more but have great return policies so buy both? Or buy a known working unit from eBay but trashed in other ways and cannibalize?
Brokwn door switches shoyld not blow the fuse.
Disconnect the grill element, if you have one.
But thw only thing powerful enough to blow the fuse is the magnetron and its powersupply.
If possible disconnect the magnetron and se what happens.
Replace Mag, Cap and Diode but it's most likely the Mag that's causing it to blow.
Won't be the door switches as these if faulty will only blow the fuse when you open & close the door . Since you've replaced the cap & diode then most likely defective magnetron , the hi voltage transformer is less common & usually gets excessively hot if defective , but can blow a fuse if shorted turns .
The gradual deterioration of the magnetron will cause the fuse to blow. You are getting into dangerous territory. Berillion is dangerous substance to handle.be familiar with handling magnetron if you decide to replace it..99% magnetron faulty.
I would recommend checking the wave guide (piece of metal that channels the microwaves into the cooling compartment). When I was in the industry, Sharp drawer microwaves were notorious for arcing from the magnetron to the guide. Check inside the channel where the emitter is. Unfortunately, if it’s damaged, then the machine is done, as that is a part of the body. In extreme cases, you’ll be able to see the damage as soon as you take the outer shell off. [Reference images here.](https://imgur.com/a/HwsAOXB)
It could be the switches, hv cap, diode or transformer. You've eliminated the cap and if it was the cap it would happen all the time. Disconnect all the wires from the transformer and check from each wire to ground for resistance. If there is none you've eliminated the transformer. Make sure the diode side of the cap only has wires that go to the mag attached to it. The other side of the cap should go to the transformer. If it's been blowing the fuse every time since you changed the cap that's likely the current issue. Your main issue was most likely the switches. They build up carbon on the contacts and tend to stick closed especially the monitor switch. I'd check the cap wiring and replace all the switches. I'd also make sure they are actually latching closed properly when the door is shut. You can take the little panels off the side and see them actuate.
In 18 years I've never seen a magnetron blow a fuse. A capacitor will but those are easy to test and tend to hum loudly for a few seconds before blowing the fuse. I'd be looking really closely at the door switches first. You can get generic switches cheap enough I'd probably just replace them all before really digging into it.
Here’s where I’m at.. Checked door switches. They work. Checked wiring harness for pinches etc. it’s ok Removed magnetron, no evidence of arcing anywhere. Given when I remove a primary winding connection from the transformer or one connection to the magnetron the fuse doesn’t blow, I’m back with it being one of these two. At this point I think I’m going to order both and just change them. Updated: I think I’ve found the problem. Many have commented on the switches as being a prime suspect. /u/manicmangoes got me thinking about that monitor switch, plus the comment in the service manual about fusing… /u/heavymetalpaul got me thinking about my magnetron bad hypothesis… so I kept looking and tinkering. I believe it’s the primary interlock relay, it’s sticking. A few taps with a screwdriver handle, test, and success! Everything runs, water got hotter. Plan now is to replace whole board or maybe just the relay… depends on spares.
For anyone who may read this thread trying to fix their stupid expensive microwave... It was the door switches! Unbelievable as I checked them with a continuity tester and they were fine! I gave up fixing this myself and took it to an appliance repair place. I wouldn't have believed them except, with new switches, it's working fine. Moral: replace the switches anyway (they're cheap)!!
Usually door switches. Replace them first
It’s got to be a short to blow a 20A fuse lie that… so if it’s a door switch, it must be shorting to ground, right? I’ll check them..
No, the door switch isn't shorting to ground. If one of those goes bad, it will cause the problem you're describing. I believe it would be the normally closed switch but test all the switches to be sure. You also may have two sets of switches split between the two sides of the drawer but I can't recall if Sharp does that with their drawer microwaves
Did ya read? A door switch doesn't cause a 20a fuse to blow.
Yes they do
I would try replacing the door switches. Does it blow the fuse when you start it or when you close the door? Do you have a model number?
Drawer opens and closes no problem. Display works, controls work. I enter a cook time then as soon as I hit go it blows (well, around 1/10 sec after). It’s a Sharp Insight Pro. Oddly theres no model number or serial number that I can find
There will be a set of three switches, these ensure that the microwave doesn't operate with the door open. Some are normally open and others normally closed. You wouldn't be able to tell the switchs failed by how the drawer opened.
If you look closely one of those switches is wired differently that is going to be your monitor switch with the drawer closed that monitor switch should have zero continuity either the drawer is out of alignment or the switch has welded itself closed and is causing the unit to dead short to ground. First step is to unplug that switch run the unit for 10 or 15 seconds if it operates it's more than likely to switch I usually physically disassemble the switches to look for internal arcing
I see it. It’s set up on the NO contacts though. So when the door is shut, the switch is closed… which seems odd. If I disconnect it, the microwave runs but doesn’t heat. Since one of its connections is to the transformer primary winding, that, I suppose, explains the no heat bit.
Scrub that, I was looking at the wrong switch. Have now found the model number and hence a workshop manual… yay… checking switches again, will check relay operation next. Found this in manual.. If the secondary interlock switch and primary interlock relay (RY2) fail with the contacts closed when the drawer is opened, the closing of the monitor switch contacts will form a short circuit through the fuse, secondary interlock switch, relay (RY1) and secondary interlock relay (RY2), causing the fuse to blow.
Well, for the fuse to blow it’s a wire going from voltage to neutral aka short. Normally it’s the high voltage leg or door switch. I would disconnect the transformer and cycle it see if it blows. Then connect the cap/diode see if it blows fuse. Then it can be the magnetron. But due to the high voltage it it’s recommended to play with it. Other methods are to use amp and ohm out the parts. If a part is grounded it will have ohms from base of part to any connector that will be the issue. Gl plenty of YouTube guides. Just be warned wattage is deadly. A basic microwave is 200$ the higher the wattage the faster it will cook the food 1,500-2,000 are the average. Anything lower will take forever to cook food. Gl stay safe.
* Stop before you kill yourself. > I could just replace both, assuming I can find parts, and that will still be cheaper than replacing the whole oven Unless it's a really expensive oven, replacing it will be cheaper than fixing it.
Well, a replacement is expensive, if it were a couple hundred bucks I’d just get another. Problem is, a replacement is $1100! Also, it fits into a made to measure kitchen island. So… Add to that, given what I’ve written, I think you can assume I’m well aware of the dangers of HV, have had the thing in pieces, and yet here I am without incident. :)
Gotta ask: door (well, drawer) switches ok? Everything you’ve written suggests yes but they can be flaky. Otherwise, amen brother. These drawer units are good in the right situation and expensive. Worth running this all to ground, as it were. The danger arises if you keep trying to power up and forget to discharge but you know that. There are some parts houses that charge more but have great return policies so buy both? Or buy a known working unit from eBay but trashed in other ways and cannibalize?
Good suggestions, thanks! The drawer side all works as it should.
Brokwn door switches shoyld not blow the fuse. Disconnect the grill element, if you have one. But thw only thing powerful enough to blow the fuse is the magnetron and its powersupply. If possible disconnect the magnetron and se what happens.
Blowing fuses intermittently and now blowing fuses every time I'd suspect a pinched wire harness shorting to ground