Samsung MC28h5015cs Combi-Microwave Oven Repair
Recently the Samsung Microwave oven of my sister’s friend no longer heated up with microwaves. After that only the heater elements in this Samsung mc28h5015cs Smart Oven could still be used as a regular oven.
The internal 5KV 800mA HV glass fuse was defect and I found small metal splinters in one side of the oven. But not clear was from where those metal fragments came. The HV diode tested fine when measured with a voltage of about 9V DC on its Anode. The HV diode cathode was connected directly to the metal ground of the oven. The oven heater elements in total use 1500 Watt of power.
And the Microwave oven part uses 1400 watt of max power. In total this oven needs a firm 2900 Watt of power. And there was no short in the HV capacitor and its capacity and ESR value were fine.
And all temperature safety fuses were fine too. So it was logical to assume that the OM75P type microwave generator was the culprit here. One safety fuse was placed on top of the OM75P ‘tube’ and another one on the cover that housed the internal light. No other defects were found. The heater elements and other fuses were fine too. And a new OM75P generator and new HV fuses with fuse holder were ordered. In the meantime while still waiting for the new parts to arrive the oven was being used as regular oven. That has many selection options as next front panel photo shows.
Following photo shows how the top of the MW generator type OM75P is mounted with only 2 screws. The symmetrical bottom side of this ‘tube’ doesn’t need 2 extra screws because there the generator just firmly slides into 2 metal holder openings of the oven housing.
The HV diode is connected with its Anode to the HV capacitor and with its Cathode directly to metal ground (Earth). Following photo shows how the fuse holder with defect 5KV 800mA glass fuse was mounted. (HV transformer output goes through HV fuse to the second male faston connector of the HV capacitor).
A new OM75P tube was surprisingly just about 25 euro free shipping. And 3 glass 5KV 0.8A HV fuses with universal holder were less than 5 euro including shipping costs.
Sadly one side of those HV glass safety fuse holder wires had the wrong 4.8mm female faston connectors where only 6.3mm were needed on both sides. Strangely the seller didn’t take notice on my request for only 6.3mm fastons. So much for the statement ‘universal’ fuse holders. Why I also had to order 6.3mm female faston connectors to replace the wrong 4.8mm wire side. And therefore also a special quite expensive HS-40J universal crimping tool with 9 different exchangeable jaws for all kind of connectors was ordered.
Another odd thing was that the new ‘tube’ looked different because some of the cooling plates inside the new metal housing of the OM75P were placed on top of each other instead of at some distance to each other like in the original ‘tube’ was the case. But luckily the Microwave oven worked again like new after the replacement OM75P was installed and connected. However time will tell if the internally differently placed metal cooling plates have a shorter life span or some other issue.
To make sure that the generated Microwave energy matched the on the label given Power rating I also measured the amount of energy that was used. And that exactly matched the given value of 1400 Watt! Next photos show the transformer with label and the front panel wiring. Followed by the new OM75P tube with the protective package in which it came.
Above last photo shows why we here need to order new 5KV fuses complete with holder because the wires with fuse holder are simply undetachable soldered or other ways fastened onto the defect glass fuse. Previously I already tried in vain to remove the wires with their fuse holders from such a defect fuse with my hot air solder station and also with my Ersa MS6000 solder station. And the only time I finally was able to remove both fuse holder wire sides from the defect glass fuse those holders were the wrong too wide size for the regularly used smaller glass fuse size.
But the fuse holders ordered for this repair had the right universal detachable fuse holders that can be re-used by simply replacing the glass fuse. Apart from the one side wrong used size female faston connector. And those glass HV fuses also can be bought separately too!
As in other Microwave repairs here the HV transformer with HV diode and HV capacitor act as a voltage doubler circuit to provide about 4000V DC to the ‘tube’. About 2KV AC comes out of the transformer that charges the HV capacitor thanks to the rectifying HV diode. And as soon as the polarity of the transformer AC voltage changes and the diode no longer conducts and no longer rectifies and no longer charges the capacitor, both HV cap voltage and the 2KV transformer voltage add in the circuit up to a total of about 4KV DC. The transformer at the same time also provides current to the tube’s filament.
After testing the oven by successfully heating up food and cooking some milk the oven was brought back to my sister’s friend. And only if the fully repaired Samsung oven still works to their full satisfaction in about 3 months from now, I am happy to collect something for the repair and the
ordered parts. But that is because we never can be completely sure about the quality of the new received parts that may vary in design, specs and so lifespan.
And bad luck happens like I recently experienced again when I had to return a very expensive almost brand new and hardly used Minisforum UM790 Pro mini computer with 64GB DDR5 memory and 1TB SSD installed back using expensive Express shipping to Aliexpress (an address in Hong Kong). Apparently the manufacturer had sold me a partly defect computer with AMD graphic processor that failed to work at refresh rates higher than 60 Hz! Where refresh rates up to max 144 Hz were promised! Sadly the AMD graphic driver kept repeatedly reporting that the hardware had still faults all related to a partly defect AMD chip on its mainboard. (AMD gpu and cpu are most likely one chip module and require a complete replacement of the mainboard and this computer they are integrated on). My 27 inch Asushom monitor easily handles refresh rates up to 165Hz which revealed the problem with this Minisforum UM790 computer. Which may likely have resulted in buyers that are completely unaware of this issue when more Minisforum computers with faulty GPU processors are sold!
I did have a 2 year warranty on this special computer but it already took me at least 4 months before any service was given. And at this moment I am still waiting on a new replacement Minisforum pro computer that hopefully this time is correctly made and also decently tested which it probably wasn’t! (or this fact was known but secretly hidden?).
Anyway, this was another easy Microwave oven repair at almost no cost that hopefully will last longer than the just about 6 years it previously had survived thus far without giving any problem.
Sadly only a service-friendly well known manufacturer like Tektronix made, and probably still makes, products that easily last 30 years or more!
Albert van Bemmelen, Weert, The Netherlands.
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Note: You can read his previous article on Brandnew HDMi 3 to 1 switch box behaving erratic from strangly behaving bad led port 2
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Albert van Bemmelen
January 2, 2024 at 10:19 pm
Update about the in the article mentioned Minisforum UM790 Ryzen 9 Pro computer: Apparently also the in the meanwhile received new replacement mini computer had the same issue with the AMD gpu driver. That kept reporting it still needed additional PCI upgrades that apparently could nowhere be found.
This driver was still missing: Device PCI\VEN_1002&DEV_15BF&SUBSYS_B0021F4C&REV_C1\4&18a4ba32&0&0041
But after a whole day of online updating the refresh rate finally could be set to a monitor frequency upto 144 Hz max. So although the AMD gpu driver still failed to completely update without afterwards always giving this fail report, the AMD gpu was not at all defect as was told by Minisforum!
Which meant that the previous computer was returned to HongKong for the wrong reason. Therefore Minisforum should in fact warn any buyer for this AMD driver error that exists but is no reason at all to assume it is defect! That wrong Minisforum assumption did cost me an extra +100 euro for express shipping and import custom fees that were not compensated!
Also be aware that most cheap HDMi switch selectors only work at low 60Hz refresh rates! (That was not why my AMD gpu refresh rate previously only worked at 60 Hz because it didn't work when it was directly HDMi cable connected to my monitor either).
Yogesh Panhchal
January 5, 2024 at 5:08 pm
Albert, Be specific when buying third party products, Just check technical requirement of the device for the purpose you are Buying for. this type of products most of the time gives compatibility issue.
this type of tiny Computers are made only for dust free & cool environment and are difficult to repair because of availability of Spares; all ports like HDMI/ USB/VGA from the out side it looks normal but from the inside it has different package which can not be replaced with normal one.
I still prefer to use Normal ATX form factor PC.
Albert van Bemmelen
January 5, 2024 at 10:35 pm
Understood. The Minisforum UM790 AMD Ryzen 9 pro computer was especially bought for 3D scanning purposes and for editing and compressing video files. The 64GB DDR5 with 1TB ssd with 16 AMD gpu cores is so much faster than our normal big tower computers and probably cheaper too.
For instance instead of waiting for a file to convert to MP4 in about 2 hours it now only takes about 12 minutes to convert.
ATX form factor computers always require a lot more space and an expensive mainboard with matching expansion cards and they probably use more power too and are never really expandable either. They also are limited to the used main processor core and maximum size of memory that can be installed. They for sure never easily go up to 64GB of DDR5 RAM why these new mini computers are the state of the art!
Parasuraman S
January 3, 2024 at 12:09 am
Another head-reeling article with complex explanations of technicalities handling two subjects, which of course had relations of its own. Many thanks for sharing your expert handling experiences and technological explanations.
Waleed Rishmawi
January 3, 2024 at 8:54 pm
good job on the detailed repair stuffed with information. about the fuses? you have to order them on line all the time? I always buy faulty microwave ovens and use them for parts and these fuses are always available. it is a very good idea to keep parts in the shop for such repairs. have a blessed day
Albert van Bemmelen
January 3, 2024 at 9:24 pm
True but I rarely find such old used microwave ovens.
Although I found one last year with a still good but used HV 1uF 2100V DC max capacitor in it that fixed my Samsung Classic 700 Watt microwave oven that had a shorted HV ecap after +30 years of use. And afterwards I wrote an article about that oven here on Jestine's blog. I also try to collect spare parts but I do not have a shop neither a lot of space left. So these days I mostly collect small smd parts with Arduino and other microcomputer module parts to make new test equipment and other stuff with.
Yogesh Panhchal
January 5, 2024 at 8:23 pm
Good Job! Albert
Imoudu.O
January 6, 2024 at 5:59 am
Albert
Most of problem-ladden devices come from china, so avoid buying from there if you can.At times i use stuff from scrabs.Thanks for sharing.
Andrea Del Corso
January 8, 2024 at 1:07 am
Come sempre..un ottimo intervento con relative spiegazioni!Grazie per la condivisione di tutte le informazioni.
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As always...an excellent post with explanations! Thanks for sharing all the information.
Albert van Bemmelen
January 12, 2024 at 9:27 pm
Update about the mentioned MINISFORUM Venus UM790 Pro Mini PC AMD Ryzen 9 7940HS computer in the article. The replacement pro computer I received afterwards also reports the mentioned device driver issue that another update is still needed. However according to Minisforum that device message can simply be ignored because all their computers with that AMD gpu show that same message which doesn't effect its graphics performance. This AMD device is recognized as PCI-bus196, device 0 , function 0.
But the previously also reported device error that amdwddmg is not started is gone now after another AMD driver update online on 6 januari 2024. It now shows oem52.inf is configured in the Events window of this device driver.
And as promised Minisforum now refunds at least so much as my Express shipping costs for returning the first UM790 Venus pro mini computer to HK. Although I also paid now twice for VAT and import handling fees to Customs. Which also was about the same as the Express shipping costs were. (>70 Euro!)
The first AMD gpu showed vertical lines on my monitor screen, and refused to display refresh rates higher than 60 Hz why it was returned to HK.
Everything now works splendidly !, and I now no longer think that it was a bad idea to buy this superfast and compact Minisforum Ryzen 9 pro computer. Which only uses at max about 120 Watt of energy from a mini matching 6.35A 19V power adapter. It also has a huge 64GB DDR5 size of memory and a 1TB ssd and runs on a superfast processor.
The computational power of this superfast mini computer will be very needed for 3D scanning (Kinect2 and Creality CRscan01), and also for electronic simulations.