How to Troubleshoot & Replace Samsung AP4219754 / DE47-20034A Microwave Temperature Control Thermostat

Watched u-tube 

After trouble shooting found open circuit on one of the protective thermostat 

Unplugged unit, Tested all the thermostats after bleeding off any existing voltage. Found the thermostat at the top of microwave that rests against the ceiling of microwave had gotten a piece of food stuck to it and caused it to overheat. The contacts were melted. Cut wire, crimped on new leads, replaced thermostat and unit fired right back up. $5 fix. Took about 35-45 minutes to take microwave down, take off shroud and rewire and replace thermostat. 

The Thermal fuse (Thermostat) had blown during normal operation, making the microwave inoperative. Replacing the thermostat solved the immediate problem, though why the fuse blew in the first place is unknown. This is a convection microwave oven and the interior normally bets pretty high. I think this is a design problem, and purchased several of these thermal fuses, 

Looked up the problem on your Web site. Checked the location of the thermostats and found the problems. The parts were an exact fit. And over night service. I will house your site again. 

I googled the SMH9187ST model number for the shut down problem. I found a you tube video that showed how to repair the same issue. I was able open up the microwave without removing it from above the range. I first unplugged the microwave. Then, I unscrewed two Philips screws from the front top of the case. This allowed the top plastic grill to slide to the left and then off. This exposed the one screw that secured the front panel. After removing that screw, the front panel slid up, and I was able to tilt it forward. I did a visual inspection. I found that the nylon insulation on one of the spade connectors had a scorch mark. This spade connector was attached to Temperature Cut Out (TCO) thermal fuse. I measured the impedance across that TCO. It was 45 ohms. According to the schematic, I found online, that TCO should be normally closed (less than 1 ohm). I found the parts breakdown online. There was second TCO in the same vicinity. Since the parts illustration was did not clearly identify which of the two part numbers went with which device, I decided to buy replacements for both TCO's. I ordered the TCO's on the weekend. They were shipped Monday, and I received them Tuesday. The faulty part was marked "KSD-120LC 0". One of the parts I received had the same marking. This corresponded to the part in the bag marked with the manufacture's part number DE47-20059B. After swapping out this part, I reassembled the microwave. My Samsung microwave is working fine now. 

Removed the panel, checked the connections. Bypassed the thermo parts I ordered with a paper clip, it worked, ordered the bypassed part and replaced, no sweat, thanks for the videos you tube... 

Internet search pointed the problem (most likely) to the thermostats and door switches. I used a multimeter to check the continuity of the parts and found problems w/ the thermostat. I did not need the switches but I misdiagnosed door switch. You need to test continuity w/ the yellow switch pressed in; this is the same as the door being closed. I tested it w/ door open which will show that the circuit is "broken" and not continuous, a rookie mistake. I replaced the thermostat and everything works fine. The actual installation is a no-brainer but it's the research / troubleshooting that the most difficult part. So do your research so you don't end up ordering unnecessary parts. 

Looked on internet for problem solution, checked thermostat with multitester - it was defective. Ordered new part, arrived in a few days. Replaced old thermostat and had it working in 30 minutes. 

Checked thermo fuses had one that was bad.