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c) Check transistors Q2, Q3, Q4 and Q5. Be sure that they are the proper type and that the emitter, base
and collector leads are in the correct holes as shown in the assembly instructions.
d) Check that the resistors just installed are the correct values as shown in the assembly instructions.
e) Check the components just installed for bad solder joints and solder bridges.
f) Check the hook switch and wires to the PC board.
9. Turn the power supply OFF. Disconnect the voltmeter. Disconnect the 1kΩ resistor and the red wire from
the power supply terminals.
10. To reverse the voltage polarity to the diode bridge, connect the free end of the 1kΩ resistor to the negative
power supply terminal and the red wire from the modular jack to the positive power supply terminal.
11. To set the power supply voltage, connect the positive voltmeter lead to the positive terminal of the power
supply and the negative voltmeter lead to the negative terminal of the power supply. Turn the power supply
ON and adjust it to 48VDC on the voltmeter.
12. To again measure the input voltage to the diode bridge, connect the positive voltmeter lead to the positive
power supply terminal and the negative voltmeter lead to point "C". Record the Input Voltage: __________
13. To measure the output voltage of the diode bridge, connect the positive voltmeter lead to the cathode of D1
(point A in Figure 6-12) and the negative voltmeter lead to the anode of D2 (point B in Figure 6-12). Record
the Output Voltage: ___________
14. To obtain the voltage across the diode bridge, subtract the Output Voltage (step 13) from the input voltage
(step 12). The difference should be between 1.3 and 1.9VDC. If the voltage difference is not within these
limits, then unplug the telephone cord from the modular jack and:
a) Be sure that the telephone is off the hook (hook switch not depressed).
b) Check diodes D1 through D4. Be sure that they are installed according to the polarity markings on the
PC board.
15. Put the receiver to your ear and gently tap the microphone. You should hear the tapping from the receiver.
If you do not hear the tapping, then unplug the telephone cord from the modular jack and:
a) Check that the speaker wires are connected as shown in Figure 6-11.
b) Check that the microphone is connected as shown in Figure 6-9.
c) Check that transistors Q2 through Q5 are the proper type and that the emitter, base and collector leads
are in the correct holes as shown in the assembly instructions.
d) Check the components just installed for bad solder joints and solder bridges.
16. Have your instructor inspect the transmit-receive circuitry and verify the tests performed.
Instructor's Approval: _________________________
17. Turn the power supply OFF. Disconnect the power supply and unplug the telephone cord from the modular
jack. Leave the resistor. It will used again for the dialer tests.
18. To avoid breaking the speaker wires, unsolder them from the PC board (see Figure 6-11). Leave the wires
connected to the speaker. They will be reconnected later.
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