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TRANSMIT - RECEIVE TESTS (Using a power supply)
Before completing the assembly, we will want to power up and test the Transmit-Receive Section. See Figure 6-12
for these tests.
48VDC
Power Supply
+
1kΩ 5W Resistor
Type A
Type B
Green
Red
Red
CAUTION: This test and succeeding tests involve 48VDC. This voltage is potentially hazardous. Use great
care when working with these voltages. Always turn the power supply OFF before touching any wires on the
power supply, PC board or modular jack.
Test Equipment Needed (not provided)
• 48VDC power supply
• 1kΩ 5W resistor
• 48VDC voltmeter
1. Turn the power supply OFF.
2. Solder one side of the 1kΩ 5W resistor to the wire from the modular jack as shown in figure 6-12
3. Connect the other side of the resistor and the other wire from the modular jack to the 48VDC power supply
as shown in Figure 6-12.
4. Plug the telephone cord into the modular jack.
5. Set the voltmeter to read 48VDC and connect as shown in the Figure 6-12. Position the PC board so that
the telephone is off the hook (hook switch not depressed). Turn the power supply ON and adjust it for 48VDC
on the meter.
6. To measure the input voltage to the diode bridge, connect the negative voltmeter lead to the negative power
supply terminal and the positive voltmeter lead to point "C". Record the Input Voltage: _________
7. To obtain the voltage across 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 the figure). Record the
Output Voltage: ___________
8. To obtain the voltage across the diode bridge, subtract the Output Voltage (step 7) from the Input Voltage
(step 6). 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.
Green - Type A
Red - Type B
Modular Jack
Red - Type A
Green - Type B
C
Green
Telephone Cord
Figure 6-12
-19-
B
A
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