ATT System 25 Installation And Maintenance Manual

MAINTENANCE
Table 4-B lists the test points (-5 V, +5 V, -48 V, and GND) for the power supply.
The test points are located on the upper-right corner at the front of the cabinet.
Table 4-C lists the voltages used by the CPs and symptoms
voltages are missing. This information is useful in diagnosing
power distribution problems.
Table 4-B.
Power Supply Test Points
that occur when
power supply or
TestVoltageRemarks
Points
Limits
+5+4.80+5. 15The green LED on the power supply
monitors this particular voltage...

MAINTENANCE
Table 4-C.Circuit Pack Voltage–Symptoms
Voltage/+5 volts-5 volts-48 Volts
Circuit Pack (Notes)No+5 VNo-5 VNo-48 V
Call Proc. (ZTN82,xSystem FailurexEIA FailurexETU Activated
ZTN1 28) for RI
Memory (ZTN81,
xSystem Failure----
ZTN1 27) for RI
CPU/Memory (ZTN129,xSystem FailurexEIA FailurexETU Activated
for R2, ZTN130
for R3)
STARLAN (ZTN84)xCP FailurexCP Failure-
-
Service Ckt (ZTN85
xSystem Failure
----
or ZTN131 (R3)
Hybrid Line (ZTN79)xCP FailurexNo VoicexStation OS
Tip/Ring (ZTN78)xCP...

MAINTENANCE
Each power supply has one green LED on its front that can be seen through
the fan assembly. The LED is visible through the ventilation slots on the front
cover, but the cover must be removed for diagnostic and service purposes.
This LED is always lighted when the system is receiving 5.1 volts power. The
LED is dark when there is a failure in the +5 volt power supply or power
connections, or when there is a short on the backplane.
If the green LED on the power supply is dark, first make sure...

MAINTENANCE
AC DISTRIBUTION UNIT
AC CIRDVARISTOR PWB
ASSY CM 538A1S1 SW
TO 15A
120 VAC
OUTLET
GROUND
BLOCK
Figure 4-8.AC Power Schematic
4-68 

MAINTENANCE
Power Supply Protection
Power supply outputs are protected from damage when they are subjected to
either momentary or sustained short circuits.“Shutdown” current protection
is provided at 125 percent (plus or minus 5 percent) of full load for each dc
output. Current foldback is provided for the 90 V ac output.
Output power is removed when the output voltage exceeds an internally set
trip point. The trip point is set at the factory at +6.25, +0.75 V for the +5.1 V
output for all rated line and...

MAINTENANCE
Power Supply Replacement
To replace the power supply, follow these steps:
Danger:Hazardous voltages are present on some backplane
1.
2.
3.
4.
5.
6.
7.
8.
pins. Unplug power cord from the outlet, and wait at
least 5 minutes before removing rear cover or power
supply.
Remove the front cover of the cabinet.
Remove the four No. 6-32 screws at the corners of the fan
assembly.
Unplug the fan assembly from system power by removing the two
modular plugs on the left side of the assembly.
Set the fan...

MAINTENANCE
Fan Assembly Trouble
The fans should always be operating when the system is receiving ac power
and the cabinet switch is turned on. If the fans are not operating, be sure that
the system is receiving ac power.
if the system is receiving power and the fans are still not operating, the ac
power connection to the fan assembly is faulty or the fans themselves are
faulty (for example, burned out motors).
To check the ac power connection to the fan assembly, first unplug the
power cord, and then...

MAINTENANCE
Overheating Trouble
A clogged or dirty air filter can cause the cabinet to overheat. The cabinet air
filter rests on the floor of the cabinet under the CP carrier. The air filter
should be inspected on any service call and replaced as needed (with air filter
comcode 845948348).
Caution:
To replace the
Warning:Check underneath cabinet for paper and other debris
that could clog the air filter and cause the cabinet to
overheat.
air filter, pinch it in the center and pull straight out.
To reduce...

MAINTENANCE
TEST POINT CABLE CONNECTSI
HERE. ACCESS VOLTAGE TESTADDRESS PLUG POSITION
POINTS FROM FRONT OF
(SLOT 08 NOT USED)
CABINET.
Figure 4-9.System Cabinet Backplane Wiring Side (Sheet 1 of 2)
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MAINTENANCE
Figure 4-9.System Cabinet Backplane Wiring Side (Sheet 2 of 2)
4-74