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Electronics Timer Repaired
My brother gave me his kitchen timer that had a completely broken buzzer. It still did work as perfect timer but gave no sound anymore after it had fallen a few times. Likely because the magnet on the back of the device was not strong enough to stick firmly onto the refrigerator. And became quite useless afterwards.
This repair may not be all that exiting but it at least explains in detail how mini buzzers work and are constructed. In this case we speak about DC buzzers. There also are piezo buzzers and AC door bells, but they need AC signals to produce any sound. And door bells are simply connected to the secondary of a transformer (about 8V AC) and activated when the outside pushbutton is pressed.
The manufacturer of this timer is unknown, and it may not be very expensive, but it is very easy to operate this timer. We just press the SEC button to set the Seconds value, and/ or the MIN button to set the Minute value. After we press the START/STOP button the timer counts down until the set time reaches ‘0000’. And at that moment the buzzer will sound for about 60 seconds. Resetting any set time can simply be done by simultaneous pressing the MIN and SEC buttons.
The timer only needs one AAA mini penlight to work. And can also be very useful outside the kitchen when we for instance want to take a nap but do not want to miss our favorite television show or movie.
I wasn’t able to repair the broken buzzer successfully because the sound volume was sadly very low. So I ordered a couple of these mini buzzers at this link.
After I first received these they were a little bit too high, but I just was able to fit the new buzzer in the timer housing.
Although these buzzers do have a + and – pin connection, connecting the buzzer wires wrong doesn’t kill it, but it just will produce less sound. These buzzers oscillate on their own on a DC voltage of about max 5V. And do not have or need any chip inside.
I tested the buzzer on my linear regulated power supply and around 5V it needed about 200mA to function which is way too much for a battery operated timer. Therefore I checked the current of the timer after the defect buzzer was replaced with the new one at a voltage of 1.5V DC. It was very low and much lower than when the buzzer was directly connected to the DC voltage of my power supply. Which probably means that the buzzer somehow is DC PWM controlled by the timer chip. In the right frequency the buzzer is able to oscillate. But it seems that these buzzers are now out of stock.
I also ordered these similar mini buzzers which I am still waiting on:
Above photo on the right shows the back of the housing inside of the timer. It shows the battery compartment with its two wires, and in the top on the right the position of the round buzzer.
Below the inside front timer housing with LCD and the 3 button board. And on the right the other side of the board with broken off buzzer and the timer quartz.
Above photo shows exactly how these buzzers internally are designed.
I tried to repair the broken coil wires by soldering them back to the + and – connections on the buzzer. That worked but sadly the membrane produced too little volume afterwards to be heard. Next photo shows the measured coil resistance.
The specification of the new received mini buzzers stated that they have a resistance of about 16 ohm at max 5V. So my digital meter could deviate a bit from the exact value, or the new buzzers themselves are a little different. (And of course the meter’s internal fuse is here measured too).
Previous photos show what remains of the defect original buzzer. The membrane that produces the sound is not shown but was placed above the with the coil wound core in the photo on the left. And the wires normally go down and connect to the small pcb as shown on the photo on the right.
Last photo showed the magnet and the plastic housing of the buzzer in which the core with coil is placed. Followed by a diagram of this FZ0669P buzzer that shows at what frequency the most decibels are produced. And also shown the size in mm of this buzzer. Max dB is about 85dB at around 30mA at a nominal voltage of 1.5V. Its resonant frequency is 2048Hz. Even if the timer itself did not cost much, repair is still preferable because these mini buzzers are very affordable. In case given timer is out of stock, buying a new mini buzzer therefore is a very good choice. These buzzers are often also used in Arduino projects. After the mini buzzers were received in about 3 weeks of waiting, the timer was fixed in no time!
I examined the internal buzzer construction further after I had removed the membrane and magnet from the core with the about 16 ohm coil on it. And after a voltage of max 5Volt DC was applied to the repaired coil it still did oscillate! To my surprise it even without membrane or the round magnet produced sound! As it turned out they only amplify the sound.
It is a little wonder what exactly makes this small coil with core oscillate. But it must have something to do with the metal in its core and the attached bottom plate. Something we do not read about in the datasheets.
I noticed that the coil got quite hot while applying the quite high current to the oscillating coil but it didn’t damage it. And the magnet and membrane (the round metal cone plate) only enhance the buzzer in reducing the necessary DC current like in paper cone loudspeakers.
Below are two links for magnetic buzzer:
The timer is as new, and like very often, again another repair at minimum cost.
Albert van Bemmelen, Weert, The Netherlands.
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Note: You can read his previous repair article in the below link: