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...

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...

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...

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...

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...

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...

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...

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...

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,...