Daewoo microwave oven repair

[goodpsusearch]

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.

[sam_sam_sam]

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

[goodpsusearch]

Originally Posted by sam_sam_sam

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

[momaka]

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.

[goodpsusearch]

Originally Posted by momaka

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

[momaka]

Originally Posted by goodpsusearch

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.

Originally Posted by stj

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.

[sam_sam_sam]

Originally Posted by momaka

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

[stj]

invertor microwaves are probably cheaper to make thanks to the filth on the metals-exchange pushing the price of copper through the roof!

[SluggerB]

Where are the diodes in your repair? I cannot see anything in the picture matching the ebay link you shared

[momaka]

^ 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.

[goodpsusearch]

I haven't yet seen a microwave oven with rusty cabinet. This is Panasonic not some cheap Bulgarian brand such as Arielli which is very popular here in Greece for the very low prices of its product line.

I don't know where this was stored, but the inside of the cooking chamber shouldn't rust like this. The oven doesn't look too old too to justify this level of oxidation.

[momaka]

Originally Posted by goodpsusearch

I don't know where this was stored, but the inside of the cooking chamber shouldn't rust like this. The oven doesn't look too old too to justify this level of oxidation.

I know, but unfortunately I've seen this quite often on my local classifieds with various modern microwaves (and occasionally some old ones too, but a lot more rarely - seems the old stuff are indeed better built/welded/painted.)

Originally Posted by sam_sam_sam

They used to sell special microwave paint for touch bad spots for inside the microwave shell

But I have not seen any for a very long time

Yeah, people just don't want to bother fixing anything anymore. A lot of things are getting too cheap to the point where it's cheaper / less effort to throw away the old/broken and buy new. And it seems more and more appliances make designs that are "not user-serviceable".

In regards to the touch-up paint... mine certainly needed more than just a few "touch-ups"

Originally Posted by redwire

Never seen rust in ovens, but habit is to leave the door open after cooking to air it out.

I suspect that's part of the reason why, too. Seems people just don't bother to clean up their spills and don't air out their MW when cooking something for very long nowadays. Otherwise, I doubt the relatively high humidity where I live (at least in the summer and parts of fall and spring) could do this kind of damage. After all, our MW is over 20 years old and still no signs of rust spots anywhere in the chamber. There are a few small ones starting to show up on the door where it bumps into the chamber (so I'm guessing the opening and closing of the door after all these years started these spots, and they eventually grew a bit... but still far from being anything significant.)

On that note, I grew up in Eastern Europe in the 90's, when getting a new appliance (especially a "Western" one like a microwave) was almost like a family celebration, lol. One of our more "wealthy" (at the time, anyways ) neighbors got a MW in the early 90's, and you bet they treated it with the utmost care.

But now? No one really cares, I think. Just use, abuse, and throw away when it's broken, then buy new again.

Originally Posted by eccerr0r

Considering that it costs $12 to mail something to my parents if it's 2 pounds and $18 if it got to $3, shipping heavy copper + laminated iron MOTs is part of the overall cost that shift towards transistors and flyback transformers...

Yup.
Well, it's a saving all the way around. Copper is getting more and more expensive - often to the point where it's cheaper to put several complex ICs and a complex overall design, just to save a little bit of copper in a transformer or wherever else. Of course, back when ICs and transistors (especially high-power ones) were expensive, it probably did make more sense to keep designs simple with less of these and more heavy passive parts. Just look at any wall adapter - despite having a few 10's of components and ICs, if not more, it's still cheaper than a regular iron-core transformer... and offers better regulation and lower standby consumption too (not to mention wide voltage input most of the time as well.)

[goodpsusearch]

Originally Posted by sam_sam_sam

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 )

BTW the oven still working and warming my food every day

Originally Posted by SluggerB

Where are the diodes in your repair? I cannot see anything in the picture matching the ebay link you shared

here:

https://www.badcaps.net/forum/attach...9&d=1611525320

https://www.badcaps.net/forum/attach...0&d=1611525320

on the bottom right, near the large AC capacitor

[sam_sam_sam]

They used to sell special microwave paint for touch bad spots for inside the microwave shell

But I have not seen any for a very long time

[eccerr0r]

Considering that it costs $12 to mail something to my parents if it's 2 pounds and $18 if it got to $3, shipping heavy copper + laminated iron MOTs is part of the overall cost that shift towards transistors and flyback transformers...

Speaking of microwave troubles, my 1.5KW oven had bad caps that ended up destroying a relay. I jury rigged another open frame relay to replace it as I didn't have a sealed one in my junk pine, I'd expect it to fail due to environmental issues (cooking vapors) but so far it's still working, and I still haven't ordered that "correct" relay.

And my parents already threw out two microwave ovens due to rust...

[redwire]

I found a Panasonic inverter microwave oven in the trash, took it apart and yes it's very light no heavy transformer. Instead it's all electronics, IC's IGBT. It' s battle of high tech that china, korea can not come up with or understand, and good old heavy low tech.

My microwave oven is dying, I can see the light bulb flicker bright/dim constantly so something is cutting out intermittently. I tried putting it on a power meter but it averages the readings and next I should try a fast ammeter.

Never seen rust in ovens, but habit is to leave the door open after cooking to air it out.

[stj]

Originally Posted by redwire

My microwave oven is dying, I can see the light bulb flicker bright/dim constantly so something is cutting out intermittently. I tried putting it on a power meter but it averages the readings and next I should try a fast ammeter.

put a couple of turns of wire around the live wire and hook your scope-probe to it.
you should get inductivly coupled current on the screen.

[eccerr0r]

Anyone bodge fix microwave oven diode failures with a pile of 1N4007's?

[redwire]

I think they are too slow switching, I know 1N5408's are worse and blow up in series, when I used three at 2kV.
Even though it's a 50/60Hz sine-wave, the dV/dt is very fast and it takes over 5usec for the diode to turn off, and by then they aren't splitting the voltage across them equally and poof. Maybe if you used a bunch of matched parts it might work. Fast-recovery is needed I think.
A CL04-12 is 12kV at 450mA and around 13 diodes in the string for American Semiconductor, vs 10 at hung lo. But no switching (off) time spec given.

[stj]

that gets me thinking, i wonder if a microwave oven diode or maybe 2 in series can be used to repair old crt monitors or scopes with the diode in the anode cable.
those old fuse-shaped diodes are almost impossible to find now.