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Old 01-24-2021, 03:56 PM   #1
goodpsusearch
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Default Daewoo microwave oven repair

One day my microwave oven stopped heating.

It would turn on and rotate the plate but no heat.

I removed the cover and checked components with digital multimeter.

Found that the high voltage fuse was blown.

This is not the AC fuse, if the AC fuse was blown then the oven would appear totally dead.

Then I tried to find replacement fuse on local electronic parts stores and this specific value was not available so I got the closest I could find.

I replaced fuse and tried to heat up a glass of water.

Strange noise was coming from the oven when it gave power to the magnetron, but the familiar noise of the magnetron generating the heating waves was not heard and the water not heated. Instead, I could smell some burnt electronics/plastic smell coming from inside the enclosure so I turned it off quickly and checked again.

The fuse, being of bigger current size, doesn't burn any more but something has definitely failed inside the oven.

Then googled "microwave oven works but no heating" and stumbled upon this video:

https://www.youtube.com/watch?v=9BUalRbhWG4

Turns out that on the magnetron connectors (that contain some capacitors inside), one of the connector is arcing to the case of the magnetron.

So, I ordered connector and HV diode from aliexpress/ebay. HV diode looked discolored from heat but was not able to test it with digital multi-meter (appeared open, DMs cannot test HV diode except if it's shorted). I thought it would be a good idea to replace it anyway.

So, I replaced the connector and diode and the oven now works as new!

One think I did different from the repair in the video linked above, I did not use screw terminal for the new connector terminals, I just soldered them to the magnetron as you can see in the pictures uploaded. The original terminals were welded. I hope it lasts.
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Old 01-25-2021, 08:35 AM   #2
sam_sam_sam
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Default Re: Daewoo microwave oven repair

One comment I have for you is as follows

I would have wrapped the wire around the terminal and then soldered it so you would have a solid mechanical joint plus a solid soldering joint as well

Because what you might notice is a few months from now that the stress from heating and cooling of the heater element might cause it to crack [ soldering joint ] and cause connection issues ( also vibrating of the magnetron might also cause the same problem )

I have work on some microwave ovens in the past and never seen this type of failure before

On this note where did you find this connector that you replaced could please post the website link to it

Thank you for posting your finding in this forum
__________________
9 PC LCD Monitor
6 LCD Flat Screen TV
30 Desk Top Switching Power Supply
10 Battery Charger Switching Power Supply for Power Tool
6 18v Lithium Battery Power Boards for Tool Battery Packs
1 XBox 360 Switching Power Supply and M Board
25 Servo Drives 220/460 3 Phase
6 De-soldering Station Switching Power Supply 1 Power Supply
1 Dell Mother Board
15 Computer Power Supply
1 HP Printer Supply & Control Board * lighting finished it *


These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps

Last edited by sam_sam_sam; 01-25-2021 at 08:48 AM..
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Old 01-25-2021, 06:49 PM   #3
momaka
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Default Re: Daewoo microwave oven repair

Nice work getting it fixed!

I also like that this is the older type microwave oven with line-connected transformer and cap instead of the newer "inverter" technology ones that are constantly popping here on my local Craigslist for free due to going bad more frequently.
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Old 01-27-2021, 03:03 PM   #4
goodpsusearch
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Default Re: Daewoo microwave oven repair

Quote:
Originally Posted by sam_sam_sam View Post
One comment I have for you is as follows

I would have wrapped the wire around the terminal and then soldered it so you would have a solid mechanical joint plus a solid soldering joint as well

Because what you might notice is a few months from now that the stress from heating and cooling of the heater element might cause it to crack [ soldering joint ] and cause connection issues ( also vibrating of the magnetron might also cause the same problem )

I have work on some microwave ovens in the past and never seen this type of failure before

On this note where did you find this connector that you replaced could please post the website link to it

Thank you for posting your finding in this forum
Well, I should have thought this earlier, now time will tell how long it lasts..


I bought the HV diode I replaced from here:

https://www.ebay.com/itm/5pcs-HVR-1X...72.m2749.l2649

Here is a link to the connector:
https://www.ebay.com/itm/5Pcs-Electr...72.m2749.l2649

Quality seemed to be OK but they had some visual differences (it's 5 pcs lot), they were not identical.

You can also buy the connector with screws and nuts as a kit ready to replace the shorted one from here:

https://www.aliexpress.com/item/4000...775b6555vbJAfM
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Old 01-27-2021, 03:05 PM   #5
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Default Re: Daewoo microwave oven repair

Quote:
Originally Posted by momaka View Post
Nice work getting it fixed!

I also like that this is the older type microwave oven with line-connected transformer and cap instead of the newer "inverter" technology ones that are constantly popping here on my local Craigslist for free due to going bad more frequently.
I have only heard of those inverter microwave ovens but I haven't seen one. I suppose they would be expensive, compared to the old ones. And you telling that they fail more frequently gives me another reason to not like them
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Old 01-31-2021, 10:52 AM   #6
vasser
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Default Re: Daewoo microwave oven repair

its troblesome
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Old 01-31-2021, 11:22 AM   #7
stj
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Default Re: Daewoo microwave oven repair

invertor microwaves are probably cheaper to make thanks to the filth on the metals-exchange pushing the price of copper through the roof!
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Old 02-03-2021, 11:58 AM   #8
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Default Re: Daewoo microwave oven repair

Where are the diodes in your repair? I cannot see anything in the picture matching the ebay link you shared
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Old 02-11-2021, 08:06 PM   #9
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Default Re: Daewoo microwave oven repair

Quote:
Originally Posted by goodpsusearch View Post
I have only heard of those inverter microwave ovens but I haven't seen one. I suppose they would be expensive, compared to the old ones. And you telling that they fail more frequently gives me another reason to not like them
Well, the problem with inverter ones is that any simple issue on HV/magnetron will usually destroy the inverter MOSFET/IGBT, HV diodes, and sometimes driving circuitry too. So it can get complicated (and often not worthwhile) to repair.

See, on yours, it was just a bad connection which blew out your HV fuse and HV diode. You replaced the fuse, but not the diode and didn't fix the connection at first. And with that, all you got was bad buzzing, but nothing sustained any major damage. So you fixed the bad connection and HV diode, and everything worked fine after that.

Now if this was an inverter MW, the inverter MOSFET/IGBT would have probably failed too, along with a bunch of other stuff. Basically, these inverter microwaves are similar to the inverters in LCD monitors... just made for higher voltage and much higher power output... and don't usually shut down gracefully like LCD inverters do when there is a problem. Instead, electronic parts often get sent to orbits until a fuse somewhere finally opens. In short, everything works nicely until one part fails. After that, it can all go haywire very quickly.

If you haven't seen one inside, here is one I parted out a long time ago:
https://www.badcaps.net/forum/showpo...&postcount=250
https://www.badcaps.net/forum/showpo...60&postcount=8
^ Basically, it was badly rusted and not worth the effort to repair. So I sent the parts to someone who needed them to fix another MW and scrapped the metal bits.

On that note, those "stainless steel" appliances aren't so stainless steel inside.

Quote:
Originally Posted by stj View Post
invertor microwaves are probably cheaper to make thanks to the filth on the metals-exchange pushing the price of copper through the roof!
Exactly.
The inverter transformer is tiny compared to those line-connected ones. Also don't need a huge cap and can instead get away with much smaller PP / film caps, due to higher frequency. So those inverter micros are cheaper to make.

Last edited by momaka; 02-11-2021 at 08:12 PM..
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Old 02-11-2021, 08:38 PM   #10
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Default Re: Daewoo microwave oven repair

Quote:
Originally Posted by momaka View Post
The inverter transformer is tiny compared to those line-connected ones. Also don't need a huge cap and can instead get away with much smaller PP / film caps, due to higher frequency. So those inverter micros are cheaper to make.

https://www.badcaps.net/forum/attach...6&d=1363046489
Is that all of what in this type of microwave oven really
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Old 02-13-2021, 01:27 AM   #11
momaka
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Default Re: Daewoo microwave oven repair

^ Yup, that's it.
You get a line bridge rectifier in the top left of that heatsink, a few polypropylene caps (I think one is for filtering the rectified line from the bridge, while the others are for the inverter HV section), and an IGBT or MOSFET (also mounted on the heatsink). Then there's the transformer, which is pretty small compared to the old chunky ones, and the HV diode connected on it. But that's all there is to it, really.
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