8-3. FAULT IN SPECIFIC STATION ONLY
Find the cause according to the following table if the fault
lies with a specific station only, not with all stations.
CHECK-ITEM
CAUSE
Dialing can not
be made at privacy
off mode.
LMU Lamp is
off.
* Disconnection of both T & R-Lines.
* Guard resistor 330
ft
on LMU is
burned out due to T & R-Lines
short.
Specific Lamp
on LMU is
brighter than
normal.
* T & R-Lines are shorted.
LMU Lamp is
on in normal.
* Fault in the station.
(Replace PCB board.)
Specific key does
not operate.
Replace the
station and
make sure that
the station
is not faulty.
* Fault in key board switch or
matrix circuitry.
* Fault in the dial generator.
(Replace PCB board.)
Calling tone can
not be heard.
Dialing tone can
not be heard on
dialing.
Sound from the
other party can
not be heard.
Same sympton
remains even
if the station
is replaced.
* Short or open in R-Line.
* Fault in the demodulation cir-
cuitry on LMU.
(Check LM-380, MT-547.)
Becomes normal
if the station
is replaced.
* Disconnection of R-Line or im-
proper connection of the station
connector.
* Fault in MT-547 on LMU.
* Station fault.
Sound is not trans-
mitted to the other
party.
Same sympton
remains even
the station
is replaced.
* Short or open in T-Line.
* Fault in the modulation cir-
cuitry on LMU.
Becomes normal
if the station
is replaced.
* Fault in MIC circuitry of the
station. (Replace MIC or PCB)
On dialing, noise
is heard by the
called party.
Same sympton
remains even
the station is
replaced.
* One of T-Lines is disconnected.
Becomes normal
if the station
is replaced.
* Fault in MIC element.
* Fault in T-Line of the station.
* Low frequency oscillation of
MIC AMP. (Faulty bypass capaci-
tor)
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