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
Ground
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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 FailurexNo VoicexStation OS
Analog Line (TN742)
xCP FailurexNo VoicexStation OS
MET Line (TN735)xCP FailurexNo VoicexStation OS
Loop Start (ZTN77)
xCP FailurexNo VoicexTrunks OS
Grd Start (ZTN76)
xCP FailurexNo VoicexTrunks OS
DID Trk (TN753)xCP FailurexNo VoicexTrunks OS
Tie Trk (TN760B)
xCP FailurexNo VoicexTrunks OS
Aux Trk (TN763)
xCP FailurexNo VoicexAUX. Eq. OS
Data Line (TN726)xCP Failure----
Tone Det (TN748)xTone Failure
---
-
Legend:
Notes:1
CP—Circuit Pack
ETU—Emergency Transfer Unit
OS-Out-of-Service
X—indicates that the voltage is used by the associated CP.
.Ringing voltage (not shown on table) is used by the ZTN78 and TN742
CPs. Associated stations will not ring if a ringing voltage problem occurs.
2. TN746B same as TN742
3. TN747 same as ZTN76 and ZTN77
4. TN762 same as ZTN79.
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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 that the cabinet
is receiving ac power.Be sure that the fans are running, that the connection
to building ac power has been made correctly, and that the power rocker
switch is in the ON (1) position.See DANGER below. Then check the
internal power connections (see Figure 4-8).
Danger:The power cord must be unplugged before the rear
cover is removed. Simply setting the power switch to
OFF is not sufficient.
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AC DISTRIBUTION UNIT
AC CIRDVARISTOR PWB
ASSY CM 538A1S1 SW
TO 15A
120 VAC
OUTLET
GROUND
BLOCK
Figure 4-8.AC Power Schematic
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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 load conditions.
Output power is removed when the power supply overheats for any reason
(for example, fan failure or operation outside ambient temperature limits).
Once the cause of the shutdown is corrected, remove ac power for about 5
minutes. The green LED (visible through the fan slots on the front of the
cabinet) will light when the power supply recovers. If the green LED is not
lighted, remove ac power a second time.If green LED is still not lighted,
remove all ac power.Repeat procedure a third time; if the LED is now
lighted, there is a short.Find the short, and either repair it or have it
repaired.
Although the power circuits are designed to withstand lightning surges on the
ac line with proper grounding, it is advisable to provide supplemental
protection with external protectors in high lightning activity areas.
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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 assembly aside in a safe place.
Unplug the 3-prong ac power connector that supplies building power
to the power supply. This connector is located at the bottom front of
the power supply.
Reach into the cabinet, between the power supply and the port
carrier. At the rear of this narrow space is the multipin dc power
connector that connects the power supply to the backplane.
Remove this connector by squeezing the tabs on the top and bottom
of the plug and pulling the plug up and away from its receptacle.
Remove the four No. 10-24 screws on the left side of the cabinet
(viewed from the front). These screws secure the power supply in
position.
Pull up on the top lip of the power supply and carefully slide it out of
the cabinet. The power supply rests on the cabinet floor. There are
no additional anchors or guides.The power supply weighs about 4
pounds.
To reinstall a new power supply, follow the preceding steps in
reverse order.
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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 remove the four No. 6-32 screws at the corners of the
assembly. Carefully lift the fan assembly away from the cabinet. Check the
two modular plugs attached on the left side of the assembly. If the plugs are
securely attached, the fan assembly itself is faulty and must be replaced.
To replace the fan assembly, remove the modular plugs at the left side of the
assembly. Reconnect these plugs to a known good fan assembly, and
reinstall the new fan assembly by setting it in place in front of the power
supply and replacing the four No.6-32 screws at the corners of the
assembly. (Without fans, the power supply will overheat and the system will
automatically shut down.)
Danger:Whenever the power supply shuts itself down (due to
overheating, shorting, etc.), unplug the power cord and
wait at least 5 minutes before restoring power.
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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 risk of fire, air filter must be in place during
operation.
Backplane and Cabinet Trouble
The backplane provides power, TDM bus connections, and station and trunk
interconnections. Each carrier has 12 universal slot positions. Any port CP
can be installed in any slot.Connection to the corresponding stations or
trunks is made through the backplane to the appropriate cross-connect field.
Danger:Hazardous voltages are present on some backplane
pins. Unplug the power cord and wait at least 5 minutes
before removing the rear cover.
Figure 4-9 provides a rear view of the cabinet backplane (rear cover must be
removed). Typical backplane pin designations are noted on Figure 4-9 for
pins 355, 254, and 056 located on slots 4, 3, and 1, respectively. Address
plug locations for Cabinets 1,2, and 3 are also noted. The address plug
position assigned slot 8 is reserved for future use. Seven leads (BAO through
BA6, see Figure 4-10) are tied to corresponding logic levels to uniquely
identify each CP slot in the system, including multiple cabinet systems. The
logic values on leads BA4 and BA5 are used to identify the cabinet (Cabinet
1, 2, or 3) and are tied through the cabinet address plugs to either +5 V dc or
ground, as appropriate.Lead BA6 is tied to ground.
An address plug inserted on a cabinet’s backplane (pins 19 and 20) at slot 5
designates the cabinet as Cabinet 1, slot 6 = Cabinet 2, and slot 7 = Cabinet
3.
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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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Figure 4-9.System Cabinet Backplane Wiring Side (Sheet 2 of 2)
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