Repair of 31 Year Old Samsung Microwave Oven
My +31 year old Samsung model M6146 Microwave oven manufactured in december 1991 suddenly last week after a loud bang ended its lifelong service. Luckily I still had another old 800Watt working microwave oven to cook my meals in the meantime. Which gives me plenty of time to fix my old Samsung Classic Collection oven waiting for the new replacement parts to arrive.
See manufacturing date ‘1991 12 02’ in above photo! Which was just about a few months after I had my own apartment in 1991. In that period (+31 years!) until yesterday 17-2-2023 this microwave oven worked splendidly. All that time serving my life saving hot meals and drinks! Until the 0.91 uF 2100WVAC capacitor apparently shorted with a big loud bang and took the 5KV HV 0.7A safety fuse with it.
About replacing the original now shorted HV 0.91uF capacitor by for instance a used good 0.97uF also 2100(W)VAC capacitor, it probably won’t make much difference. And after observing all the adverts on these HV caps it seems that they often sell slightly different values around the 1uF value only depending on the value that at that moment was measured. And all for the same price.
So even if we search to order for that exact 0.91uF capacitor it still will be uncertain if we will get that exact same capacitor delivered to our door.
And the used good replacement high voltage 0.97uF capacitor came out a very similar microwave oven that had all the parts my Samsung had but without the special 5KV 0.7A glass safety fuse. Next photo shows the original now completely shorted 0.91uF capacitor.
Next photo shows the new glass high voltage safety fuse that was ordered:
Next photos show the completely burned through 5KV 0.7A hv safety fuse that was hidden in the white plastic holder. Followed by a photo of the Samsung label sticker that was at the oven back.
After measuring the microwave ‘tube’ filament it still showed a intact internally electron emitting spiral. Without any unwanted short to the outside metal to the anode of the mw ‘tube’. But from what I read it may still be uncertain if the ‘tube’ is still good to go when measured this way by just using our multimeter. But in case the ‘tube’ no longer heats up my meals and drinks I will know for certain it is a goner! Provided that it not again also burns through my replacement hv safety fuse that protects the secundary microwave power transformer with its about 2KV high voltage output from shorting out! Which no doubt already saved my microwave hv voltage power transformer from going to kingdom come.
And in case the microwave ‘tube’ indeed is gone I do have another spare used one to replace it with and check out.
Next photo shows the probably still good microwave ‘tube’ type OM755(31)-D with measured good filament. Followed by more photos of my longlife but momentary out of order good old trusted Samsung 700 Watt oven. That according to online info probably after all that time no longer provides the same amount of microwave power emission effectively. But still dissipates the same input power.
That is because the microwave ‘tube’ in time deteriorates slowly from its new state.
Above photo shows the front of my Samung Classic Collection microwave oven. Next photo shows the topview of my oven after the metal cover was removed. Also the one-time round metal safety temperature fuse mounted in the top of the microwave metal ‘tube’ holder (with brown and red wire in the middle) was still fine measuring a very low ohmic value. And also the long glass 8A 250V fuse was still fine.
Above circuit shows a clear example of how this microwave oven and many other ovens work!
Following photo shows a good close-up sideview onto the OM755(31)-D ‘tube’ and the hv power transformer. Everything looks still very good after 3 decennia of frequent daily use apart from some dust on the cooler fan. (which I cleaned up a bit after this photo was taken).
Above photo shows the used but good replacement high voltage 2100VAC 0.97uF cap that was used to replace the now original defect capacitor.
My Samsung microwave oven is back in action as soon the new 5KV 0.7A fuse is received and connected. This way again safely connecting the about 2000V coming out of the HV transformer secundary to the right connectorside of the 0.97uF high voltage capacitor. (Which is the + side of the transformer wire in the above given example circuit). So for just spending 2,26 euro (mainly on shipping!) ordering a new safety fuse, my oven will be fixed and ready. Again at minimal costs!
But anyway…Whatever you do…Be happy, always stay safe and try to be successful!
Albert van Bemmelen, Weert, The Netherlands.
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Maurice
March 3, 2023 at 7:59 pm
Nex time Albert you can order the high voltage fuse also at for example farnell. Thats faster. But i think that repair shops have them.
In dutch
Je kunt ze ook bestellen bij winkels als farnell. Daar komen die van mij vandaan. Maar ik denk dat er ook genoeg andere winkels ze kunnen hebben.
Ik heb er 10 bij farnell meebesteld met vrienden en kreeg er per ongeluk 50. Maar mocht ze houden van van farnell. Dus ik heb er voldoende. Mocht je er nog nodig hebben vraag maar aan jestine of je mijn mailadres mag hebben. Dan stuur ik er op, ik woon in Nederland
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You can also order them from stores like farnell. That's where mine come from. But I think there are plenty of other stores that can have them as well.
I ordered 10 from farnell with friends and accidentally got 50. But if she likes farnell. So I have enough. If you need any, just ask Jestine if you can have my email address. Then I will send it, I live in the Netherlands
Albert van Bemmelen
March 3, 2023 at 10:53 pm
That is most friendly of you Maurice, but I already ordered 3 of them including fuseholder. Because I noticed that after desoldering the old now defect fuse inside the white holder that the fuse was thicker than standard fuses (and both wires with the thicker metal fuse holderclips were soldered onto the bigger glass fuse inside the white holder housing too!). Which meant that I needed a new 0.7A fuse with new matching plastic holder. Why I couldn't just use the old holder with only a new replacement fuse that is most likely thinner in diameter. And it can't be just any current of course either. So I appreciate your offer but now I'll just wait for the 3 ordered fuses to arrive. A few months ago I also ordered a type 25AA256-I/SN-ND IC EEPROM 256KBIT SPI 8SOIC, for making a large reflow oven (PE magazine april/may 2022). But sadly that chip is still postponed at Digikey for yet another year until march 2024! And apparently no firm is able to deliver this chip and many other chips faster. But I'm hoping that Mouser will be able to deliver this chip long before that time! (I ordered that chip from both firms since Mouser also was able to provide the necessary 32bit PIC processor were no other firm in the world could!)
Albert van Bemmelen
March 3, 2023 at 11:46 pm
PS: Je mag rustig mijn emailadres hebben Maurice. Jestine kan je die vast geven. Het kan immers altijd handig zijn een andere elektronica hobbyist te kennen. Zeker wanneer die ook in Nederland woont. Al is het maar voor uitwisselen van gewenste technische informatie. Het aantal elektronica hobbyisten in mijn eigen Woonplaats is sowieso erg beperkt. Ik zit trouwens ook op Facebook hoewel ik verder niet vaak chat of zo. Maar plaats daar zo af en toe mijn nieuwste elektronica bouwsels. Ook over 3D geprinte uitbreidingen. Met vriendelijke groet (;)
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PS: You can safely have my email address Maurice. Jestine can give it to you. After all, it can always be useful to know another electronics hobbyist. Especially when he also lives in the Netherlands. Even if it is only for exchanging desired technical information. The number of electronics hobbyists in my own hometown is very limited anyway. I'm also on Facebook, although I don't chat often or anything. But occasionally post my latest electronics builds there. Also about 3D printed extensions. Yours sincerely (;)
Albert van Bemmelen
March 4, 2023 at 8:23 pm
PS: today I luckily found the required 25AA256T-I/SN sop8 Eeprom on eBay. 5 NEW pcs free shipping here but it will not be until around the 16th of may that they will arrive.
Tito Kanshulu
March 3, 2023 at 8:05 pm
Excellent explanation, excellent repair Van Bemmelen. Keep it up
Albert van Bemmelen
March 4, 2023 at 6:04 pm
If I do Tito I'm hoping it will not be because so many devices in my home start to go all out of order! (lol)
Like my desperately needed Microwave oven.
Parasuraman S
March 3, 2023 at 8:43 pm
Well done! A good re-life work for a sturdy MO in your usual professional way!
Albert van Bemmelen
March 5, 2023 at 1:07 am
I hope the ordered set 5KV 0.7Amp fuses with matching holder won't take too long before they arrive. Because these larger devices simply take up too much space in my living room. I already had ordered products twice before in over 7 months that never arrived from Aliexpress. Like small Grease tubes specially for (3D) printers and other mechanic moving machines. I hope that
this third time ordered finally will arrive.
Albert van Bemmelen
March 13, 2023 at 9:14 pm
The above mentioned Grease tubes that were already ordered invain on Aliexpress twices before, finally arrived last week on 10 march after they were ordered for the third time which in all took at least about 11 months of useless waiting!
Paul
March 3, 2023 at 11:59 pm
The HV Capacitor value is probably quite critical as their accuracy is usually 3%, better than the usual 5%.
Albert van Bemmelen
March 4, 2023 at 3:26 pm
In case the deviation is indeed that critical Paul, and my replacement hv cap with 0.97uF is too far from the original 0.91uF value, it still will be hard to get the exact desired cap value as they all are measured and sold around a value of about 1uF. And if it doesn't work as espected I always can also exchange the mw-tube that came with the 0.97uF hv capacitor. But I'm hoping that won't be necessary.
Imoudu.O
March 4, 2023 at 4:10 am
Thank God that your magnetron is still in good shape, there are times when it tested good with the use of dmm, it fails on load.Thanks for sharing sir.
Albert van Bemmelen
March 4, 2023 at 5:59 pm
Indeed Imoudu, it is quite unusual that frequent daily used electronic products still work after all those years!
Yogesh Panchal
March 4, 2023 at 11:38 pm
Good Fix!Albert
Albert van Bemmelen
March 6, 2023 at 6:37 pm
Strange sellers that sells these HV Microwave capacitors. Like this seller that sells 1uF caps as universal replacement caps. But his advert also mentions free shipping at an additional shipping price of about 8,15 Euro. Which is more than the capacitor costs.
Albert van Bemmelen
March 8, 2023 at 11:33 pm
Addendum: Today 8 March 2023 two wired fuseholders with 0.7A 5KV fuses were received. Sadly both had different clips on each side with on one side the correct clip and on the other side a wrong smaller one. They both should be the normal wider clips. Like my original fuseholder was. Only after replacing the smaller clip the 5KV wire connection could be restored and my old Samsung microwave oven was fixed and working like a brandnew oven!
Waleed Rishmawi
March 9, 2023 at 4:10 pm
in my country it is very difficult to find such high voltage fuse in the hard ware stores i mean but I go the junk yard very often and buy broken microwave ovens and I always find some that is still intact and of course use the other parts for the repair in the shop. it is time consuming but eventually I will order a lot on Ali express and keep them in the shop just to save time going to the junk yard. thanks for sharing and have a blessed day
Albert van Bemmelen
March 9, 2023 at 6:52 pm
With those clips I of course meant the Faston type! (Dutch: Kabelschoen)