Microwave Beeper, noise reduction, Modification

Our Fridgidare microwave Model FFCM1155US has a very harsh, annoying, and ear piercing beeper to indicate that the microwaving done. Also it continues unless you press the off button, which is sometimes difficult to press correctly. There is a way to get it to stop after its three beeps when you open the door, but, if you open the door during beep one, two, or three of the three beep cycle it will continue through all three beeps and then stop.

Here's how I modified the beep to be lower volume and, we think, a little less harsh. I opened the unit by removing three screws for the top/sides cover and found the beeper, on the circuit card on the left side and the "speaker" is the round thing in the black plastic holder. See Photo 1 below.

Photo 1: The Beeper Circuit Card
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I tried different capacitors and even a resistor in combination. The first tested was a 10 μf capacitor but the volume was too weak to be hard except in a quiet kitchen. Next I tried a 4.7 μf capacitors but it was also a bit too weak, low in volume, so I then tested a 1 μf 50 V capacitor across the beeper and this can be heard in the next room weakly but not two rooms away while listening to the radio or watching TV or computer youtube.

Note: The positive connection for the beeper is the outer ring of the beeper. The center connection is the return. See Photo two and three below.

Photo 2: Closeup of the Beeper
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Photo 3: Beeper Capacitor Tests
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HINT: Solder as far away from the ends of the wires attached to the beeper since the center one comes off very easily, learned from experience, and then it is somewhat difficult to solder it back on. I measured the DC voltage across the beeper while it was beeping and found that alone the beeper voltage measured about 9V. With the final capacitor the voltage was about 16V. I forgot to get out the oscilloscope to capture the wave form but I suspect it is a quarewave since it is so harsh to listen to. This means that the peak voltage could be substantually higher than the voltages measured. Because of this, and because I had many more 50V capacitors in the box than any other voltage, I used a 1 μf 50V cap which can, sort of, be seen in Photo 4. I sorry I didn't check this photo before closing up the microwave case because the capacitor is so out of focus. It can be seen to the right of the group of wires ending in the white connector.

The wire used was 24 gauge single strant wire because it was stong enough to keep its shape once wound around the wires seen between the beeper and the - out of focus - capacitor in the photo.

Photo 4: Beeper and 1 μf Capacitor
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Phil Karras, KE3FL
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