GAI-Tronics Call/Talk Installation of Call/Talk Systems - Manual (Page 4)

Pub. 42004-251A
Installation of Call/Talk Systems Page: 4 of 9
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Line Balance Assembly Adjustment
Remove the line balance assembly cover to expose the page line balance control. To set the control for
proper page circuit loading, lift the handset from the adjacent handset hook, and press the push-to-page
button. From a normal speaking distance (approximately ½ inch), blow steadily into the handset
microphone, and adjust the control to minimize receiver sidetone. This adjustment should be made only
during the initial installation of a system. However, if more than ten speaker amplifiers are added or
deleted, repeat the page line balance control adjustment.
After the final adjustment, replace the line balance assembly’s cover, and secure it with the 4 mounting
screws to discourage tampering by unauthorized personnel and to prevent the entry of contaminants.
Handset Preamp Adjustment
The screwdriver-adjusted potentiometers are located on the printed circuit board mounted on the inside of
the cover plate. R3 is the transmit level potentiometer and R13 is the receiver volume potentiometer. All
the handset preamps are factory set but may require a level adjustment due to system loading and/or long
cable runs. Party-line level checks should be approximately 0.75 V
RMS
when whistling into a handset
microphone. Adjust the transmit level if the voltage is not correct from a station. Receiver volume must be
adjusted according to the noise in the area and the preference of the user.
Speaker Amplifier Adjustment
A nameplate on the D01B module indicates the position of the thumbwheel adjustment. The speaker
amplifiers are factory set for approximately half output with a normal voice input. The output must be
adjusted to suit conditions in the area. Maximum output is 9.8 V for an 8-ohm speaker. If maximum
output is desired, whistle into a handset, and set the output for approximately 9 V for an 8-ohm speaker.
Step 6 - Troubleshooting System Problems
Hum or Buzz on the Line
A hum or buzz on the page circuit (or one or more party circuits) is usually due to either a short circuit of
one of the two conductors for each circuit to the ground or an unbalanced leakage to the ground. As long
as the two conductors are twisted pairs, and there are no significant leakage paths or short circuits to the
ground, any induced voltages are the same on both conductors and do not appear across the line.
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. By going from one junction
point to another and disconnecting the affected circuit, the ground is located. The fault could be within a
plug-in amplifier. However, most grounded circuits occur due to 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. If such isolation removes the line balance
assembly from the operating portion of the system, a 33-ohm, ½-watt resistor should be connected across
L1 and L2 of the Page/Party
®
line circuits. These resistors must be removed after completion of the tests.