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10. To measure the input voltage to the telephone, connect the positive voltmeter lead to the negative terminal
of the power supply and the negative voltmeter lead to point C. The voltage reading should be between 5
and 12.5VDC. Input Voltage: _________________
11. To measure the input current to the telephone, measure the current in the 1kΩ resistor. Connect the positive
voltmeter lead to point "C" and the negative voltmeter lead to the negative power supply terminal. The
voltage reading should be between 35 and 45VDC. Resistor voltage: _______________
12. Have your instructor verify the DC tests just performed.
Instructor's Approval: ________________
VOICE TEST
- Refer to Figure 6-20 for the voice test configuration.
1. Turn the power supply OFF. Connect the components, including the oscilloscope, as shown in the Figure 6-20.
2. Set the Ringer switch to ON and position the telephone so that it is off hook (hook switch not depressed).
Set the tone/pulse switch to the pulse position.
3. Set the voltmeter to read 48VDC. Turn the power supply ON and adjust it for a reading of 48VDC on the
voltmeter.
4. Set the oscilloscope as follows:
Coupling
Sweep
Sensitivity
6. Speak into the microphone in a normal voice. The peak-to-peak amplitude of the voice signal on the
oscilloscope should be between .2 and .5V. Voice signal amplitude: ________________
7. Set the oscilloscope as follows:
Coupling
Sweep
Sensitivity
8. Press the 8 button and sync the oscilloscope on the positive transition of the input signal. You should see
the telephone input voltage waveform shown in Figure 6-14. The peak-to-peak amplitude should be 35V
minimum. Input voltage amplitude: ________________
9. Have your instructor verify the Voice Tests just performed.
Instructor's Approval: ________________________
10. Turn the power supply OFF.
RINGER TEST
- Refer to Figure 6-21 for the ringer test configuration.
1. Set the variac to 0 and connect the variac, isolation transformer, 1kΩ resistor, modular jack, and voltmeter
as shown in the Figure 6-21. Do not connect the telephone cord.
AC
10mS / Division
0.1V / Division
DC
50mS / Division
10V / Division
-28-
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