GAI-Tronics 700 Series 120 V AC Page/Party Systems - Manual (Page 6)

Pub. 42004-139D
GAI-Tronics 700 Series Page/Party
®
Systems Page: 6 of 10
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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 both
conductors are twisted pairs and there are 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 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. If such isolation removes the line balance
assembly from the operating portion of the system, connect a 33-ohm, 0.5-watt resistor across L1 and L2
of the Page/Party
® line circuits. Remove these resistors 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. Speech 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 will affect gain and increase the level of sidetone. Please
refer to specific instructions above 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. Locate the short circuit in the same manner as locating a ground, by checking
junction points with an ohmmeter.
Cross Talk
Cross talk, or 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.
In a multi-party line system, it is possible to have a small amount of cross talk between channels if line
balance resistors are opened or not connected. This condition can be detected by the presence of high
sidetone in the handset.