AT&T System 25 - Manual (Page 240)

MAINTENANCE
Once a faulty CP is identified, it can be replaced using the procedures in
“Reseating and Replacing Circuit Packs” under “Routine Maintenance. ”
Refer to the information in “Circuit Pack LEDs” under the “General
Maintenance Information” 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
ZTN131 [R3]) or Tone Detector (TN748). Replace the faulty CP.
Frontplane Ribbon Connector Trouble (Release 1 Only)
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
If a major malfunction occurs, the system may activate the 109 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 CPs (Cabinet 2 or 3) will
shut down all devices connected to that cabinet but will not shut down the
entire system.
Check the green LED on PS (visible through the fan slots on the front door).
If extinguished, PS is shut down.
Remove ac power from the cabinet for
about 3 minutes. Turn on ac power. Green LED lighted, PS overheated (fan
defective), or current overload. Check all boards in cabinet for problems.
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