User's Manual

Lucent Technologies — Proprietary
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22-12
401-660-100 Issue 11 August 2000
Linear Amplifier Circuit (LAC) Maintenance
voltage is removed from the LAMs, thereby shutting down the RF output
power of the LAC.)
Multiple LAMs in alarm due to tripped breakers are the most common cause of
CRITICAL alarms. Other possibilities include multiple blown LAM fuses or failed
LAMs, although it is unlikely that the number of LAM failures would have been
allowed to progress to this level. This type of failure is indicated by multiple lighted
LAM LEDs at the cell site. See LAM Alarm Procedures.
NOTE:
When a CRITICAL number of LAM failures has been detected, 5-volt LAM
bias is turned off, shutting down the LAMs, and a CRITICAL alarm is
issued. The radios on the LAC will be blocked from service by the ECP in
response to the CRITICAL alarm. Once the LAMs shut down, or RF is
removed, LAM failures can no longer be detected (except for a blown fuse)
and the CRITICAL alarm will clear after about a 5-second delay. If radios
are re-applied before the cause of the CRITICAL alarm condition is
corrected, the cycle will repeat.
An LAM bias fault will also generate a CRITICAL alarm on C-Series LACs and is
indicated by simultaneously lighted LINEAR AMPLIFIER UNIT and LINEARIZER
LEDs (See Figure 22-11) at the cell site. See LAM Bias Fault Procedure.
High-level thermal alarms indicate that the LAC has overheated. The LAC will shut
itself down when its temperature reaches this level and will remain shut off until its
temperature falls to the mid-level. Overheating may be caused by the LAC being
overdriven or may be due to an LAU fan failure. This alarm will be preceded in
time by low-level (MINOR) and mid-level (MAJOR) thermal alarms and should not
be allowed to progress to the high level. (A cell site air conditioning failure should
not cause the LAC to heat up to the high-level, as long as the LAU fan is
functioning properly.) See Thermal Alarm Procedure.
SANITY Alarms
SANITY (MAJS) alarms indicate that the LAC is not responding correctly to
queries by the UN166 Alarm/FITS Interface (AFI) Board in the Radio Channel
Frame. Common causes include mis-addressed LACs, faulty alarm cables, and
incorrectly installed LAC microprocessors. SANITY alarms may also be caused by
a damaged alarm circuit in a LAC or in a UN166/AFI board.
In the presence of LAC SANITY alarms in a cell, view all LAC alarms with
suspicion. One mis-addressed or otherwise "insane" LAC will often confuse alarm
reporting for all LACs in the site. Cell 18 (paragraph B) illustrates a situation where
3 LACs are reporting SANITY alarms, as well as other alarms. This is most likely
the result of a problem with only one of the LACs.