Now in wide assortment watches are sold cheap. They have typical defects. So, I bought a watch with a calculator and alarm clock had a very quiet signal and "ran" up to 11 with a day.
After disassembly it became clear the reason for the quiet sound - Board in the corner there was printed conductors for the installation of a surface mount transistor. One conclusion (emitter) connected to the minus of the battery, the other (collector) - with spring contact of the piezo oscillator and the third (base) led to the chip clock. Between the base and the collector was a jumper. As a result, the crystal was supplied AC the voltage amplitude of up to 1.5 V.
The revised scheme is shown in Fig. 1.
Due to the lack of the planar transistor was installed CTA, and his body slightly crooked with a file. The Inductor L1 wound on a ferrite ring Chsh wire diameter 0.08 mm, number of turns - 650. It was established experimentally: the more turns the better. To strengthen the conclusion coils are wound in such a thin wire, in a known manner: fold the end of the wire several times to burn the varnish with a match or lighter, and then to clean fine sandpaper or a soldering iron on the aspirin.
With said throttle signal amplitude reached 12 In and the sound was heard at all room. To slightly change the tone of the signal by selecting a capacitor between the collector and emitter. The throttle stick in the right place, and the jumper circuit Board between the base and the collector slit.
The transistor in the absence of signal was closing well - the current consumption is not increased.
To adjust the clock rate is usually mounted capacitors of small capacity between the findings of the quartz resonator and the common wire (or "plus" source power). The Board has the pad for a capacitor surface installation. However, the installation of the condenser is practically not changed the speed. When you control the oscilloscope revealed that the amplitude of the voltage at the other output the quartz resonator is less than 4 times ("cold" output). When installing the capacitor 15 pF between this pin and the positive power care hours was less than 0.5 C per day.
In Fig. 2 schematically shows the elements and contact pads.
Author: V. Ananiev, Yaroslavl