Microwave blowing fuses


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Old 02-05-16, 05:11 AM
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Microwave blowing fuses

Hi All.

I have a microwave device.
It worked fine for a few years.
Lately, after heating something up, the interior of the microwave had some steam in it.

Trying to put something else inside to warm up, I heard the magnetron starting up (the characteristic hard click and the following buzz), and the fuse blew a fraction of a second later.

I thought it was because humidity shorted out something.
(Although it operated a few times in the past after having some steam inside it)

After waiting a few days, and replacing the fuse, another try to warm something
resulted with the same phenomenon.
The fuse blew again, after the magnetron started up.

Searching for some answers, it seemed that it might be the door micro-switch.

Looking in the device, there were 4 micro-switches on the door locking mechanism.

Although all of these switches look the same, two of them seem to close the circuit when the door is open, and two of them seem to close the circuit when the door is closed.
(none of then seem to stay in the open or closed position permanently).

Can it be safe to say that these switches operate correctly ?
They do change from open to close (although not all of them in the same direction)

If these switches are functioning correctly -
what would be the next thing to check ?

Many thanks in advance for any advice and/or hint.
 
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Old 02-06-16, 01:01 AM
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Welcome to the forums.

You didn't leave a make or model so I can't answer your questions directly.

Usually if you hear the magnetron start and then the fuse blows..... the door switches are not your problem.

You could have a defective high voltage diode, HV capacitor, or magnetron.
 
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Old 02-07-16, 12:51 AM
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Thank you for the welcome, and for the quick reply.

The microwave oven does not carry any famous brand name on it.

Internal components seem to have Hyundai name on them (I'll take a closer look at the exact make and model of the main components sometime soon).

So, considering the parts mentioned, will it be worth the cost/trouble to replace these parts ?
 
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Old 02-07-16, 05:18 AM
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Counter top no, over the range maybe depending what is wrong.
 
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Old 02-23-16, 12:53 PM
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So - I had some time to play with it a bit.
The findings are:
1. Correction about the make of the internals - The Magnetron is labeled DAEWOO,
other than that, all components are printed with unknown far-east sounding names.
2. After getting some fuses - I tried disconnecting some components:
a. Disconnecting the Magnetron did not help the situation
b. Disconnecting the high voltage transformer prevented the fuse from being blown.
c. The high voltage capacitor has 1 diode connecting it's 2 leads to each other,
and another diode connecting one lead to the body of the device with
direction from the capacitor to the device body (Why would they do that ?)
3. It is a counter top Microwave oven, so as mentioned, it was nice if it could be fixed
(Both for the personal challenge and for avoiding more junk in landfills), but . . .

Thank you all for the replies.
 
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Old 02-23-16, 08:30 PM
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Playing is good but be careful. The high voltage section when operating normally runs several thousand volts and can be lethal.

The part across the cap is a bleeder resistor..... not a diode. It's job is to bleed the high voltage off the cap so that it can be handled safely. Even with that resistor it can take a while to discharge. Always use a screwdriver across it to make sure it is 100% discharged.

The following is a generic microwave schematic. The red arrow is the resistor.

Click on diagram for larger view
 
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Old 02-24-16, 10:05 AM
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Thanks for the schema.

I was wondering why they connect the diode to the body of the device -
isn't it creating a risk for someone to get a shock ?

I'm attaching a photo of the components.
The capacitor is 2100V 0.91uf
The Diode connected to the ground is HVR-1X 3 SK 1528
The "Short protector" (As it is called on the schema found on the device cover) is HVR-062 SK 1717

Looking for these parts I found:
Capacitor with the same characteristics ~ 10 USD
HVR-1X3 SK 4715 (Does that difference have any significance ?) ~ 5 USD
and
HVR 2x062H ~ 5 USD
I was not able to find any HVR 062 part only HVR 2X062 -
How bad/significant is the difference between these two parts
Again - thanks for the quick replies,
and for the patience answering questions that may seem obvious to people who are more experienced.
 
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Old 02-24-16, 10:50 AM
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If you look at the schematic I left.... you'll notice everything is tied to ground. One side of the diode is grounded as part of the circuit.

Have you checked the diode and the cap with an ohmmeter ?
A shorted component will stand out.

HVR-1X3 is a common microwave diode.
HVR 1x3 Original High Voltage Power Diode | eBay
HVR 1x3 "Original" Sanken HV Rectifier Block Diode 2 Pcs | eBay
 

Last edited by PJmax; 02-24-16 at 11:07 AM.
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Old 02-24-16, 11:16 AM
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Yes, I did :-)
I understand that the microwave body is (or at least should be) grounded,
and connecting the diode to the body connects it to the ground.
Still, I would have been more at-ease if the grounding of high voltage component is done directly to the ground, not through the device body, just for the unlikely scenario where the body's connection to the ground is broken for some reason.

Checking the components show some resistance in all directions.
It seems that the diode does not disconnect the circuit in any direction.

Regarding my previous message -
about component part number differences -
are these components identical / compatible / have the same characteristics?
 
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Old 02-24-16, 11:46 AM
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So basically you're just going to replace everything.... the shotgun method.

As far as I can tell..... the HVR-2X062 will replace the HVR-062.
 
 

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