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11. Unplug the telephone cord from the modular jack.
12. Peel the backing off of the buzzer side of the buzzer pad and place it on the buzzer as shown in Figure 6-6a.
The pad goes directly on top of the three buzzer wires. Peel the second backing off of the buzzer mounting
pad and stick the pad onto the solder side of the PC board as shown in Figure 6-6b. Note: When mounting,
be sure that you allow room for the Pulse/Tone Switch and Hook Switch.
13. Continue to the Transmit-Receive Section.
Figure 6-6a
TRANSMIT-RECEIVE
Circuit Description - The Tip and Ring inputs are fed to a diode bridge made up of diodes D1 through D4 (see
schematic diagram). The bridge insures that a positive voltage is fed to the telephone circuit regardless of the
polarity of the input. This is done to protect the integrated circuit and other components that may be damaged
by a reversal of polarity.
When the hook switch is not depressed, the telephone is ready to transmit and receive. The incoming signal
from the Central Office is sent via R20 and C6 to the speaker amplifier made up of transistor Q5. This amplifier
drives the speaker.
Transmission begins when you speak into the microphone. The microphone used is an electret type. This type
of microphone is made up of a capacitor with a dielectric material which holds a permanent electric charge.
Sound waves striking a plate of this capacitor cause the plate to vibrate and thus generate a small voltage
across the capacitor. This voltage is amplified by a Field Effect Transistor (FET) mounted inside the microphone.
The signal from the microphone is then amplified and sent to the Central Office via the local loop. A portion of
the signal is also sent to the speaker amplifier to provide the desired sidetone.
Buzzer Pad
Location of
Pulse/Tone Switch
-15-
Location of Ringer Switch
Buzzer
Hook Switch
Figure 6-6b
Location of
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