GAI-Tronics SSM110 Card Rack Assembly - Manual (Page 22)

Pub. 42004-669L2E
SSM110 Card Rack Assembly Installation, Operation, Maintenance Manual Page: 20 of 26
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07/07
Maintenance
General Information
Contact GAI-Tronics Service at 1-800-492-1212 for technical assistance.
Troubleshooting Guide
System Hum or Buzz
Hum or buzz on the paging speakers is usually due to a short circuit to ground on one of the two page line
conductors in the system cable. This condition is indicated on the access panel display and the PPI card
in the card rack.
To correct the problem, locate the source of the ground. Using an ohmmeter, check various junction
points of the system wiring to determine in which direction the ground can be located. Locate the ground
by going from one junction point to another and disconnecting the affected circuit. The fault could be
within a plug-in amplifier. However, most ground circuits occur in improper terminations or are caused
by small strands protruding from an improperly lugged wire.
Another source of grounds or near-grounded circuits is junction boxes filled or partially filled with water.
In many cases, there are deposits in the boxes, which, when combined with water, produce conductive or
corrosive solutions. These deposits cause leakage between circuits and can corrode the wire and
terminals.
Isolation of field wiring may be necessary for test purposes. When isolating a portion of the system from
the card rack, a 33-ohm 1/2-watt resistor must be connected across L1 and L2 of the page and party lines
to provide the proper audio line balance resistance. Remove this resistor after completion of the tests.
N OTE : The same tests also apply to the party lines.
Static Charges
In many normal installations, a static ac voltage may be read from the conductors of the page line circuits
to ground. In many cases this voltage may be as high as 50 volts or more. This voltage is induced into
the circuits by capacitance to the ac power circuit (generally carried in the same cable, and also from
power cables paralleling communication cables). This voltage is inconsequential and can be ignored.
Problems would only occur if one side of the page circuit becomes grounded.
Audio Voltage
In a properly operating system, audio voltage read across the page and party line circuits (L1 and L2) will
be 1 to 1.5 V
RMS
when an audio signal is present. The voltage will be proportional to the loudness of the
person’s voice using the handset.