Bell System Practices 1A Installation And Maintenance page 3

4.00
MAINTENANCE
Always remove power cord from. the
power outlet when working on control
unit.
4.01
For maintenance on control units, proceed
as follows:
• Check that power cord is connected to com-
mercial power outlet.
• Press ON button. If pilot light fails to
light, test power supply outlet with a neon-
lamp voltage tester or equivalent.
• When commercial power is entering the
control unit, and amplification seems to be
deficient in either receiver or transmitter
circuit or both, replace the amplifier unit
with one known to be serviceable.
• If changing the amplifier clears the trouble,
interchange the tubes, one at a time, from
good amplifier to defective amplifier. Orient
them so that the red mark on the tube base
faces both the top of the card and the dot
near the top end of the socket.
If this does
not clear the trouble, it can be assumed
that trouble is internal in the amplifier.
Leave serviceable amplifier in place and
return defective amplifier according to local
instructions.
Note:
Do not change amplifier gain controls.
• If trouble still persists, replace complete
control unit.
SECTION C70.201.01
4.02
Fluorescent lights, transformers, motors,
or other similar apparatus may cause an
inductive noise in the loudspeaker. Grounding the
amplifier chassis may eliminate this noise. In cer-
tain areas, local ordinances may not permit
grounding. Be guided by local instructions.
• The ground wire should be run separately
from a mounting screw inside control unit
to a radiator or an electrical conduit
system.
• If this does not eliminate noise, it can be
assumed that the ground is poor, and the
ground wire should be run to a cold water
pipe instead.
Where the regular transmitter (U1-type
receiver) is troubled by inductive inter-
ference fr.om power 3ource, the trouble
may be remedied by 'ltSing a 658A trans-
mitter ( HC3 receiver with a cpld-rolled
steel shield). These tra,mmitters are
completely interchangeable but used
onJ,y on a maintenance basis.
4.03 After working on equipment, test the com-
plete system. For lAl speakerphone test
call, refer to 3.00.
5.00 RADIO INTERFERENCE
Where radio interference is experienced in
the telephone set, a suppressor may be installed.
See C Section entitled Radio Signal Suppression
in Telephone Sets.
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