If this "solution" fixed your situation... GREAT! But for most people (read 46 pages worth) cutting power does nothing. If under warranty... sure... have a professional fix it. If not, the repair charges are more than the replacment cost. Here was my DIY fix that cost nothing, but some time. This link is on page 46 of this same thread... https://us.community.samsung.com/t5/Kitchen-and-Family-Hub/Over-the-range-microwave-oven-inputs-7-by-itself-and-prompts-to/m-p/1361952/highlight/true#M34025
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If you are reasonably handy (definition - You have screwdrivers. You know enough to disconnect the power chord), here is a fix that worked for me. Cost me some time, but no parts except some stranded wire and two wire lugs. I have a ME21F707MJT well out of warranty. My symptoms. Random keys automatically being pressed... including the lock key. Fortunately, the Start key has never activated for the potential fire hazard mentioned. Also, most keys don't work when actually pressed. And the keys that work only work some of the time. I am not a service technician. I read through much of this 46 page thread and found no DIY fix. However, I found along the way many references to a special door with GROUNDING. I just happen to fiddle with microelectronics and know the symptoms when things aren't grounded properly. It turns out, the grounding strap inside the door is expecting to reach ground via the metal hinges. This is a very poor idea for digital electronics. SIMPLY adding a wire from the grounding strap inside the door connecting to the metal chassis of the unit solved my issue completely. No random self-presses. All buttons working. The clock is now working for the first time since new. You will need to do an Internet search for your model's service manual to help you take the door apart. It was a PITA! This is digital electronics and likely running 3.3 to 5V DC. No risk of shock if you unplugged the unit. Stay away from the high voltage areas inside the chassis! Some store a charge even disconnected. Use stranded wire (must be flexible since it bends at the hinge) Only needs to be as thick as the green wire. What I used was just handy. Screw it down securely with wire lugs at both ends. Re-assemble. Enjoy. Save yourself the $400 service bill many others mentioned. Circuit board as found inside door before fix. Note green grounding wire. Add your own stranded wire to the same ground point Connect other end to any convenient chassis screw.
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