User's Manual

Lucent Technologies — Proprietary
See notice on first page
401-660-100 Issue 11 August 2000
22-11
Linear Amplifier Circuit (LAC) Maintenance
Preamp alarms are the most frequent cause of MAJOR alarms. MAJOR alarms
without accompanying MINOR alarms are almost always generated by the
Preamp, especially if they are intermittent. A bad Preamp or blown Preamp fuse is
indicated by a lighted LAC Preamp LED at the cell site. If a Preamp LED is not
visible upon entering the cell site, use the Radio Control Procedure to uncover an
intermittent preamp problem. See Preamp Alarm Procedure.
Multiple LAMs in alarm will also generate MAJOR alarms. This may involve from
2-6 LAMs, depending upon the LAC configuration. A tripped LAC breaker will
cause groups of LAMs to generate a continuous MAJOR alarm. Intermittent
MAJOR alarms of this type are usually accompanied by MINOR alarms, since
individual failed LAMs may not respond exactly the same to changing traffic
conditions. This type of LAM alarm is usually easy to diagnose at the cell site
since multiple LAM LEDs will be lighted. See LAM Alarm Procedures.
A blown FCA fuse will generate a MAJOR alarm in C-Series LACs. This may be
caused by the LAC being over-driven or may result from the LAC being powered-
up with too many radios turned on. A blown FCA fuse is indicated by a
continuously lighted LINEARIZER LED at the cell site. (A/B-Series LACs report a
blown FCA fuse as a MINOR alarm. The FCA fuse is not field accessible in these
LACs, however.)
A bad fan or a blown fan fuse will also generate a MAJOR alarm in C-Series
LACs, which is indicated at the cell site by a lighted FANS LED in combination with
another lighted LED indicating the particular fan, either LINEAR AMPLIFIER
UNIT, PRE-AMPLIFIER, or LINEARIZER. See FAN Alarm Procedure.
Mid-level Thermal alarms indicate that the LAC is about to overheat. Overheating
may be caused by the LAC being overdriven or may be due to an LAU fan failure.
These alarms will be preceded in time by low-level thermal alarms (MINOR) and
should usually not be allowed to progress to the mid-level. (A cell site air
conditioning failure should not cause the LAC to heat up to the mid-level, as long
as the LAU fan is functioning properly.) See Thermal Alarm Procedure.
CRITICAL Alarms
CRITICAL alarms are, in order of likelihood:
■
Multiple LAMs in alarm
■
A complete loss of LAM Bias Voltage
■
A failed component in the Linearizer
■
A High-level thermal alarm.
!
CAUTION:
A CRITICAL LAC alarm results in immediate loss of service and must
be attended to promptly.
(When a critical alarm condition is detected, bias