5.3
Isolating Noise Problems
If noise or hum is present on the resident’s phone line after installation of the 1812 telephone
intercom system, use the procedure on the next page to find and correct the source of the noise. This
procedure will require the use of a telephone test set (DoorKing p/n 1800-050 or equivalent).
Typically, noise is usually introduced into the system because of incorrect wiring, poor quality of wire,
wire runs exceeding maximum distances, phone and high voltage power wires running in the same
conduit or in very close proximity to each other, a wrong type transformer was substituted, or the
phone lines, power lines or 1812 circuit board is grounded.
1. Place the BYPASS switch in the BYPASS mode (slide switch to right). If noise goes
away, problem is with phone in/out wiring, power wiring, or 1812 unit. Place the BYPASS
switch in the ENTRY SYSTEM mode (slide switch to left) and proceed to step 3. If noise
is still present when switch is in the bypass mode, disconnect C.O. wires and HOUSE
wires from bypass switch. Connect the C.O. wires to the HOUSE wires. If the noise goes
away, the bypass switch is bad and needs to be replaced. If noise is still present, contact
the telephone company for service.
2. Remove all external items connected to the 1812 unit, such as back-up batteries, relay
connections, push button switches, or time clocks. All terminals should be free of any
wiring except terminals 1 and 2 (PHON IN WIRES), terminal 3 (CASE GROUND WIRE),
terminals 4 and 5 (PHON OUT WIRES), and terminals 17 and 18 (16 VAC POWER
WIRES). If noise is still present, proceed to step 2. If noise is gone, the source of the
noise is one of the external devices that were connected to the 1812. Reconnect them
one at a time until you find the item that is the source of the noise.
3. Remove the PHON OUT wires from terminals 4 and 5 at the 1812 unit. Connect your
handy phone directly to the loose PHON OUT wires. The wires should be dead and you
should not have any dial tone on these wires. If you do have dial tone, the 1812 is wired
incorrectly. Disconnect power immediately and refer to the wiring information section in
this manual.
4. Disconnect your handy phone from the PHON OUT wires (step 3). Remove the PHON
IN wires from terminals 1 and 2 at the 1812 unit. Connect the PHON IN wires to the
PHON OUT wires. This completely disconnects the 1812 unit from the circuit. Check the
phones in the house. If the noise is gone, problem is with or in the 1812 unit, or with the
power supply or power wiring. Reconnect the PHON IN wires to terminals 1 and 2, and
the PHON OUT wires to terminals 4 and 5, then proceed to step 5. If the noise is still
present, problem is with the PHON IN or PHON OUT wires running from the 1812 unit to
the bypass switch. These wires will need to be replaced and/or re-routed to correct the
problem.
5. Disconnect the 16 VAC wires from terminals 17 and 18. If the phone line is now clear,
the problem is in the 16 VAC power run. Check the power lines for a ground, or running
next to high voltage wires, or an improper wire size and insulation, or too long of a wire
run. If noise is still present, go to step 6.
6. If noise is still present at this step in the trouble shooting sequence, this would indicate a
short to ground internally in the 1812 unit. Remove the 8-pin front panel terminal strip
from the circuit board, and check for noise again. If noise is gone, this would indicate a
problem with the microphone board, speaker, push button, or lights on the front panel
assembly. Check for any shorts to ground on any of these components or wiring. Check
to be sure that none of the wires are pinched. If noise is still present, check the wires
entering the back of the 1812 box and be sure that none are pinched. Be sure that these
wires are not touching the back of the 1812 circuit board, possibly causing a short to
ground. If all of the above steps fail to identify the source of noise, contact DoorKing for
additional assistance.
1812-161-E-1-10
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