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2. Set the voltmeter to read 50VAC. Put the variac ON and adjust it to obtain 50VAC on the voltmeter.
3. Put the ringer switch ON. Plug in the telephone cord and position the telephone so that it is on hook (hook
switch depressed). You should hear a steady ringing from the telephone.
Variac
Isolation
Transformer
+
1kΩ 5W Resistor
Type A
Type B
Green
Red Red
4. Take the variac OFF.
5. To measure the AC voltage across the 1kΩ resistor, move the voltmeter lead from the red wire of the modular
jack to point "C". Put the variac ON. The voltage should be between 2 and 5VAC. This indicates that the
AC current drawn by the telephone is between 2 and 5mA. AC resistor voltage: _______________
6. Take the variac OFF.
7. Have your instructor verify the ringer test just performed.
Instructor's approval: _______________________
If any of the above tests should fail:
a) Check for broken wires on the keyboard, speaker, buzzer, hook switch, and telephone cord.
b) Check that the hook switch is seated properly against the switch button and that it operates freely.
c) Recheck the PC board for bad solder joints and solder bridges.
d) Recheck the PC board components. Be sure that all resistor and capacitor values are correct according to
the assembly instructions. Be sure that each transistor is the proper type and is installed properly.
Disconnect the test setup.
Green - Type A
Red - Type B
Modular Jack
Red - Type A
Green - Type B
Green
Telephone Cord
Figure 6-21
-29-
Telephone
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