System 412 (430-0460) Troubleshooting Faxback Doc. # 6497
This model functions on standard, loop start, phone lines just as you have
at home. It is designed to connect to two RJ14 jacks which have two lines
in each, total of 4 lines.
The home or business should be wired with standard, twisted pair, station
wire. Each pair should have a twist every two feet or less. Under no
circumstances should the flat silver colored cable be used or line cords
longer than those supplied with the phone. If improper cabling is used on
this 4 line phone or any of our other 2 or 4 line phones the customer will
probably experience crosstalk coupling. IE, they can hear another
conversation on their line.
The intercom, paging and data for line status indication is carried via RF
carrier (285kHz, 320kHz, and 430kHz) over phone lines one or three. An
intercom call can be in progress at the same time that normal phone calls
are in progress with no interference between them.
The wiring can be either "home run" or "looped". "Home run" means that
each phones cable goes back to a central location. "Looped", sometimes
called "Daisy chained" means the cable is looped from one phone to the next
in the shortest path this saving cable. The system will normally function
properly with a total of 1000 feet of station wire for all phone. If ten
phones are used in the system the average run can be 100 feet.
When running telephone cable never lay the cable adjacent to AC power
cable. Keep at least a foot or two away and cross AC power cable at right
angles. Do not run the phone cord near florescent lights. A buzzing
sound will occur on the phone line if it is too close to AC power and
florescent lights.
A. RFI - The System-412 is somewhat sensitive to 144 to 150MHz RF signals.
Those frequencies are used by ham radio operators and by local police,
and emergency services. A few cases have been documented where an
installation is a few blocks from a hospital or police station and their
radios cause calls to be dropped, lights to turn on when there is no
call, noise on the line, improper ringing, etc.
Many potential remedies have been tried but with little success. Below
is a list of things to try:
1) Keep cable lengths and line cords an short as possible.
2) Add choke cores such as the 273-104 to the line cord where it
connects to the back of the phone, to the handset cord where it
connects to the base of the phone and to the AC power cord at the
back of the phone. Depending on the length of the customers cabling
adding the choke core to the phone line could effect the maximum
length that the phones can be spaced. Check and make sure that all
phones will still communicate with each other.
3) Try moving the position of the phone in the office. Many times moving
the phone across the room will reduce the interference. This
frequently works when the interference signal is coupling directly
into the phone rather than coming in on the phone line.
4) Try moving the RF carrier switch on the back of the phone from
position 1 to 3. This switch selects the line that the intercom and
data RF carrier signal are applied to.
5) In the source of interference can be determined and the frequency is
known it is possible the phone company repair office will be willing
to help. They may be able to add an RF interference filter at the
network interface (phone company interface with the customers
building). It is important to try to isolate the interference source
first as they, the phone company, will expect the problem to be in
the customers equipment.
B. CROSSTALK - The System-412 is no more sensitive to crosstalk than any
other system. In fact all radio shack multiline phones are tested and
verified to have greater than 70dB of isolation between lines. This is
well below the audible threshold. The problem normally is caused by
coupling from one pair in the house wiring to another. Possible
solutions are:
1) Remove any long line cords or modular extension cords such as 279-
363/373.
2) Make all station wire runs as short as possible.
3) Use station wire (278-872/873/1310) to connect up phone jacks. Do not
use the flat silver cable such as 278-365/366.
4) Connect a phone at the network interface with all house wiring
disconnected. Place a call to a number that will give a long
recording such as the National Weather Service. Put that call on
hold and call someone on the other line. Listen for crosstalk. If
the problem is still there, the source is in the phone company cable.
If it is not, the problem is probably in the customers cable.
5) If the customer has a crosstalk problem and the above conditions have
been met, it may become necessary to use a separate cable to connect
each line. The cables that are already there can be used for two
lines and two additional cables will have to be added for the other
two lines. If this method is used, do not tie the cables together,
just leave them separated a little to help reduce coupling from one
cable to another.
C. LINE STATUS COMPATIBILITY - The line status indicators on this model
work by getting a digital signal from another phone on the system
telling it to light, blink or turn off a light. This is a different
method than is used on our other two and four line phones with full
line status.
The System 208, 209, 411 and some others work by sensing the DC voltage
on the phone line. Normally the phone line voltage is 48 volts when
the phone is hung up. When the user goes off hook the voltage at the
phone drops 5 to 10 volts. The phone senses this change and turns the
line indicator on steady. When the phone is placed on hold, the line
voltage increases to between ten and twenty volts. Again this is
sensed by the phone but in this case the indicator blinks. This type
system is not compatible with the digital method used in the System-
412. There is no resolution to this incompatibility other than
acquiring a compatible phone.
D. If you use a non-412 System phone/fax/device on a 412 System, the line
status will not work.
(/all-04/25/95)