Clear-Com PS-702 - Manual (Page 15)

P S - 7 0 2 T W O - C H A N N E L P O W E R S U P P L Y
2 - 3
SYSTEM CHECKOUT
Before you turn on the power:
Check Termination
There should be one and only one termination for each channel in the system.
This termination is usually set to on at the main station or power supply. To
ascertain that only one termination is present on the channel, perform the
following test:
1. Using a multimeter, measure the resistance between pins #1 and #3 on
one of the Channel A XLR connectors at the rear of the unit.
2. If the channel is terminated properly, then the resistance should measure
approximately 4 kOhm. A very high channel resistance means the
channel is not terminated. Channel resistance of 2 kOhm indicates a
double-termination. If a double-termination is indicated, locate the other
power supply or main station and set its termination to off.
Note: The location of the termination switch varies with model. On some
products, the termination switches are on the rear panel; on others
they are inside the unit. Consult the unit’s manual for the location.
3. Repeat for the other channels.
4. Check resistance between chassis ground and pin #1. Using an ohmmeter,
measure the resistance from pin #1 on the main station or power supply to
chassis ground. The measurement should read 10 Ohms. A high reading
(over 100 Ohms) indicates that the 10 Ohm resistor in the unit has failed
and requires replacement. Failure to perform the replacement will result
in an audible “buzz” in the system. A reading of less than 10 Ohms (or a
short) typically indicates that the shell and pin #1 of one of the
interconnect cables are shorted together. Test the individual cables until
the culprit is located and repair or replace the cable.
Note: Pin #1 and the shell of the XLR plug on the interconnect cables
should NOT be connected together.
Check Intercom Cable Resistance
For minimal crosstalk, the ground resistance of the intercom cables should be
as low as possible, preferably less than 2 Ohms. Disconnect an intercom line
from the main station or power supply. At the point in the intercom line
furthest from the unit, connect a clip lead jumper between pins #1 and #2.
Back at the “powered” end, use an ohmmeter to measure the resistance
between pins #1 and #2. A value of less than 4 Ohms is ideal.