GAI-Tronics 700 Series 24 V DC Page/Party Systems - Manual (Page 9)

Pub. 42004-140E
Installation of GAI-Tronics 700 Series 24 V DC Page/Party
®
Systems Page 9 of 13
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08/13
Step 7 — Troubleshooting the System
Hum or Buzz
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 ground or unbalanced leakage to ground. As long as the two
conductors are twisted pairs and there is no significant leakage paths or short circuits to ground, any
included 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 the ground location. By going from one junction point to
another and disconnecting the affected circuit, the ground can be located. 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 are 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, 1/2-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.
Feedback or Distortion on the System
Each page and party circuit must be loaded to the optimum 33 ohms using the line balance assembly. If
the line balance is not connected or is defective, the system will have excessive gain and will break into
feedback quite easily. Voices will also be distorted, and there will be a high level of sidetone in the
handset receiver.
Each party line is terminated with fixed 33-ohm resistor in the line balance assembly. However, an
adjustable control is provided for the page line to compensate for the number of speaker amplifiers
connected to the system. Improper adjustment affects gain and increases the level of sidetone. Please
refer to specific instructions in Step 6 for adjusting the line balance assembly.
Very Low Audio Level on One or More Lines at all Stations
It is possible for the system, or part of the system, to function with a dead short across the page or party
circuits. If this occurs, the level of the system will be very low, decreasing to minimum level in the
vicinity of the short circuit. To locate the short circuit, it is necessary to proceed in the same way as
locating a ground - checking junction points with an ohmmeter.
Cross Talk
Cross talk, or inter-channel interference, is generally caused by accidental crossing of circuits in a
junction box. To check for this condition, measure resistance between circuits of the interfering channels.
The resistance should be infinite or a very high value. Leakage or shorts to ground in two or more
circuits can result in cross talk on those circuits.