Some buttons on microwave oven don’t work

[chssvl]

I have a two year old Samsung MC28H5125AK microwave oven. A month or so some buttons stopped working (annoyingly, this sometimes includes the “start” button rendering the oven useless). Which buttons work and which don’t seems to change every now and then. I took appart the oven and checked the ribbon from the button pannel to the main module and it is well connected as this is sometimes cited as a fault with most microwave ovens. I even used a multimeter to check that the circuit between the two boards was OK and this is indeed OK.

Any other thoughts on what could be the problem? My guess is that the PCB control module is probably the culprit and needs replacing, but given that a replacement is about 2/3 of the price of the oven, I would hate to buy a replacement only to find out that this wasn’t the fault.

Thanks in advance

[electrofix]

the way most of these buttons work is using a sytem called a crosspoint switch. using hoizontal and vertical wires to the switches

lets say there are 4 wires vertically and 3 horizontal. if you connect wire 1 vert to wire 1 horiz you get say number 1. If you connect 1 vert to 2 horiz you get 2 and so on. what this means is if one wire breaks it affect a number of switches

this may well be just the switch membrane but i cant promise.

looking at the switch you may be able to find which wire connect to the start sw and trace it back to the connector. You can then you a multimeter to check the switch is operating although you will need someone elses help to push the button while you measure

Dave

[chssvl]

Thanks! For reference I found a picture of the switch membrane at https://ineedparts.eu/products/control-board-for-samsung-mc28m6075cs-microwave-oven-de96-01040a. So, just to make sure that I understand, what should happen is that if, for example, for the button on the lower-right it goes back to the first and third connectors in the ribbon. Then, using the continuity test function in my multimeter, if I put the leads on the first and third connectors of the ribbon and press the button, I should get a beep for continuity, otherwise the membrane might be broken, right?

Thanks again.

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[electrofix]

may not beep, some do and some dont but on a resistance scale it will go from very high to very low when its pressed

Dave

[chssvl]

Thanks Dave. Unfortunately the way the ribbon is soldered and glued to the membrane doesn’t allow me to clearly see where each connection leads. However, I used the terminals in the ribbon and tested all possible combinations of the terminals while pressing a button at a time until I got a beep (or at least a change in the resistance). So, for example, for the “stop” button I got a beep with “pins” 6 & 16. I seem to have gotten a beep, even with some of the buttons that work intermittently and a “chronic” one, but didn’t get anything with one of the “chronic” buttons. However, I might have skipped a connector when trying them all out so wouldn’t take it as a fully reliable indicator.

It is really odd. In the morning of the 14 buttons in the pannel, five (including the start button) weren’t working. After all this testing there are five that are still not working – four that were not working in the morning and a new one. However, the start button is now working. Everything else in the pannel including the display and the know seem to be working fine.

[electrofix]

thats odd as normally if its a broken address line things would not change unless the break was as it passes through the start button

there will be 3 tracks going to some buttons. one track is a common and links on to the next switch so that accounts for 2 tracks at the sw. the third track feeds the info back to the board. if the common line breaks at the switch then everything after that wont function

Dave

[chssvl]

Thanks. I ordered a new membrane and we’ll see if that does the trick or not. If that doesn’t do the trick then I’d imagine it’s the PCB. In any case, fingers crossed. Thanks a lot for the help

[chssvl]

Update. Tried out the new membrane and got the exact same problem. I’m guessing that means that it definitely has to be the PCB, right? Also, the start button has stopped working again. To be honest I’m almost tempted to just sell this MW for spares and get a new one. Quite disapponted with Samsung’s quality. Bought a Samsung TV at the same time as this MW and it also starting showing some faults after 1.5 years or so…

[electrofix]

not a great lover of samsung to be honest. phones may be ok but their domestic appliances leave a lot to be desired.

Dave

[chssvl]

Yes, lesson learned the hard way. Any recomendations in terms of MW brands? Before getting this one we used to live in flats with built-in MWs – all from brands that don’t seem to sell stand-alone ovens (e.g. Siemens). Thanks again

When I remember the Sanyo MW that my parents had and that was still going more than 25 years after they purchased it…

[electrofix]

bosch, siemans and neff microwaves are availability in both integrated and none integrated units but they all use panasonic works

Dave

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