ATT System 25 Maintenance Manual

							CLEARING SYSTEM-DETECTED TROUBLES
Interpreting Circuit Pack LEDs
During the various states of operation (start-up testing, normal operation, and
failure), CP LEDs appear as follows:
Memory [ZTN81 (V1) or ZTN127 (V2)]: The red LED on this CP lights when
power is applied and is extinguished upon successful completion of the ROM
checksum test initiated by the Call Processor CP. Failure is indicated by a
steady On red LED.
Call Processor [Z7N82 (V1) or ZTN128 (V2)]: The green LED on this CP
lights when power is applied and flashes during normal operation. When the
system resets itself, the green LED turns on and then off for a few seconds
each while the Call Processor performs its self-tests. Once testing is
complete, the green LED flashes and the Call Processor resets all port CPs.
Failure is indicated when the green LED remains steadily On or Off.
Service Circuit (ZTN85): The red LED on this circuit pack lights during self-
testing and goes off upon successful test completion. The yellow LED
flashes during normal operation, indicating that the clock generator is active
and remains On when any tone receiver on the CP is in use. Off
indicates CP not translated or a problem. The green LED is On once
translations have been loaded and remains On during normal operation.
Port CPs: The red LED on port CP lights during power-up testing and goes
off upon successful test completion. The green LED lights once translations
have been loaded and remains On during normal operation. The red LED
remains On for any port CP that fails the start-up test or fails while in use.
The yellow LED is On when any port on the CP is in use.
8-8Once the system has done either a cold or warm restart, the SAT prompts
the user with the -> after a  is entered, and normal procedures
can then be followed to read the error log, perform administrative tasks, or
sign off. 
						

							CLEARING SYSTEM-DETECTED TROUBLES
Clearing Specific System Troubles
l
l
l
l
l
l
l
l
lComplete System Failure
Common Control Trouble
Circuit Pack Trouble
Frontplane Ribbon Connector Trouble
Power Supply Trouble
Fan Assembly Trouble
Overheating Trouble
Backplane and Cabinet Trouble
Emergency Transfer Unit Trouble.
Complete System Failure
A complete system failure is caused by a catastrophic failure in the Common
Control circuitry, the power supply, the backplane, or the cabinet. Refer to
procedures in the relevant section below in the event of such a failure.
Complete system failures are rare; most failures are of a non-critical
component, such as a port on a CP.
Common Control Trouble
Failure of any of the Common Control CPs (that is, Call Processor, Memory,
or Service Circuit) is critical and requires replacement of the faulty pack(s).
Failure of these CPs can affect the entire system and may cause activation of
the Emergency Transfer Unit (ETU).
Failure of either the Call Processor or Memory circuit pack generates the
following type of error message:
FAIL: : : :
The bracketed fields contain the following information:
l  is either CPU (Call Processor) or MEM (memory)
l  is one of the following:
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							CLEARING SYSTEM-DETECTED TROUBLES
RAM TEST
ROM TEST
AA INTERFACE
DUART TEST
REAL-TIME-CLOCK TEST
BUS ERROR
WORK CYCLE
DPR TEST
MMU TEST
l specifies the specific location of the failure, such as the
address of a failed integrated circuit.
A representative common control failure message would be:
FAIL: CPU: RAM TEST: IC26:
This message identifies the failure as a Random Access Memory (RAM) test
failure in integrated circuit 26 occurring on the Call Processor CP.
After partial failure, the system continues operation and the green LED on the
Call Processor CP flashes normally.
After total failure, the system ceases operation and the Call Processor green
LED may not flash or the red LED on the Memory CP may remain steadily
lighted.
Failure can also be verified by checking the LEDs on each CP. If the Call
Processor fails, its green LED is steady on or off. If the Memory fails, its red
LED is steady on. (Note that the failure indications resemble the LED
indications during the start-up process.)
If either a partial or total common control failure is detected, remove and then
restore system power. This forces the system to perform a warm restart.
If the failure exists after system restart, remove power again and seat the
suspected faulty CP (being sure to press in all socketed devices to ensure
firm connections). Restore system power. If a common control failure
continues to exist, one of the CPs must be replaced. Determine which CP to
replace by checking the messages on the SAT and in the error log and the
LEDs on the CPs.
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							CLEARING SYSTEM-DETECTED TROUBLES
Common control error messages sometimes appear on the SAT automatically
during power-up testing. If the common control is experiencing serious
failure, error messages may appear only on the SAT and not even be sent to
the error log.
Any Memory CP problem could be caused by (1) a fault in the frontplane
connector to the Call Processor CP or (2) a problem on the Call Processor
CP itself. It does not necessarily indicate a fault in the Memory CP.
Follow the preceding instructions for Common Control CP replacement, being
sure to first save translations on tape before removing power. Replacing
either the Call Processor or Memory CP also requires the frontplane
connector to be disconnected and then reconnected.
It is also mandatory to force a Cold Start after replacement of a defective
Call Processor CP. This is done using the SAT after a restart. The Cold
Start initializes the new Call Processor with the systems CP configuration as
well as clears all status and error logs. (Old information may have been
stored on the replacement CP.)
Circuit Pack Trouble
Most CP troubles result in user complaints, discussed in Section 9 Clearing
User-Reported Troubles. Diagnosis is aided by messages in the error log
and LEDs on the CPs.
Once a faulty CP is identified, it can be replaced using the procedures in
Reseating and Replacing Circuit Packs. Refer to the information in
Interpreting Circuit Pack LEDs to understand the meaning of the CP LEDs.
If the error log notes an error related to the touch-tone receivers, the
receivers are performing below system requirements.
Touch-tone receiver problems are due to a faulty Service Circuit (ZTN85) or
Tone Detector (TN748). Replace the faulty CP.
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							CLEARING SYSTEM-DETECTED TROUBLES
Frontplane Ribbon Connector Trouble
The frontplane ribbon connector is a flat cable connecting the Call Processor
and Memory CPs at their front edges.
To reattach or replace this cable, follow these steps:
1.Remove power from the system.
2.Pull the exposed tab on the cable from one of the CPs. This exposes
a second tab at the other end of the cable.
3.Pull the second tab to remove the cable entirely.
4.Replace the cable in the reverse manner. (The cable is keyed for
correct placement.)
Power Supply Trouble
The system, due to a major malfunction, may activate the 10B Emergency
Transfer Unit. With this condition, the system may be nonfunctional, even
though the green LEDs on CPs in the other cabinets remain lighted. Failure
of the power supply in a cabinet containing only port cards (Cabinet 2 or 3)
may shut down all devices connected to that cabinet but will not shut down
the entire system.
Table 8-B lists the voltages used by the CPs and symptoms that occur when
voltages are missing. This information is useful in diagnosing power supply
or power distribution problems.
Newer models have voltage test points located on the upper right corner at
the front of the cabinet.
Older models have test points on the backplane behind the rear cover.
These test points are factory use only! Under no circumstances should the
rear cover be removed to provide access to the test points unless the power
cord has first been unplugged.
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							CLEARING SYSTEM-DETECTED TROUBLES
Table 8-B. Circuit Pack Voltages—Symptoms (Note)
Voltage/+5 volts-5 volts-48 Volts
Circuit Pack*No*No*No
Call Proc.(ZTN82,XSystem FailureXEIA FailureXETU Activated
ZTN128)
Memory(ZTN81,XSystem Failure----
ZTN127)
STARLAN(ZTN84)
XCP FailureXCP Failure--
Service Ckt.(ZTN85)XSystem Failure----
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
GD. 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:
CP—Circuit Pack
ETU—Emergency Transfer Unit
OS—Out-of-Service
* X indicates that the voltage is used by the associated CP.
Note:Ringing Voltage (not shown on the table) is used by the Tip Ring
and Analog Line CPs. Associated stations will not ring if there is a
Ringing Voltage problem.
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							CLEARING SYSTEM-DETECTED TROUBLES
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 not lighted, first check to be sure the
cabinet is receiving ac power. Be sure that the fans are running, the
connection to building ac power has been made correctly, and the power
rocker switch is On (1). See DANGER below. Then check the internal
power connections (see Figure 8-1 ).
DANGER:Do not remove rear cover to check connections before
unplugging the power cord. Simply turning off the power
switch is not enough.
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							CLEARING SYSTEM-DETECTED TROUBLES
* OLDER MODELS ONLY.
NOTE: THREE VARISTORS ARE PROVIDED. ONE VARISTORCONNECTS BETWEEN EACH OF THE FOLLOWING AC INPUTS:
BK AND WH
WH AND GN
BK AND GN.
Figure 8-1. AC Power Schematic
8-15 
						

							CLEARING SYSTEM-DETECTED TROUBLES
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 or -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, operation outside ambient temperature limits). The
power supply will recover from a shutdown automatically once the cause of
the shutdown is corrected. Recovery requires about 5 minutes with ac power
removed. The green LED visible through the fan slots on the front of the
cabinet will turn on when the power supply recovers.
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.
Power Supply Replacement
To replace the power supply, follow these steps:
DANGER:Hazardous voltages are present on some backplane pins.
1.
2.
3.
4.
5.
Unplug power cord and wait at least 5 minutes before
removing rear cover or power supply.
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 is located at the bottom of the power
supply at the front.
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. The
8-16 
						

							CLEARING SYSTEM-DETECTED TROUBLES
receptacle is mounted in the cabinet at a 45° angle relative to the
cabinet floor.
6.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.
7.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.
Fan Assembly Trouble
The fans should always be operating when the system is receiving ac power
and the cabinet switch(es) is turned on. If the fans are not operating, be sure
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, due to 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.
8-17