Mitel SX-200 ICP - 1.0 5020, Technician'S Handbook

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225
Basic Troubleshooting and Repair
Test/Verify (Loop Start)
• Verify far-end (CO) circuits by using a standard telephone set in place
of the Loop Start trunk circuit.
• Verify near-end (PBX Loop Start) circuits by connecting to a local PBX
ONS circuit.
• Check for appropriate voltages on Tip-Ring in each call state.
• During off-hook condition, 18 mA DC minimum should be drawn from
the CO (typical 25-40 mA).
• Some Key/PBX systems may be polarity sensitive; reverse Tip-Ring to
verify.
Table 41: Loop Start Line/Trunk Summary
Signal
Loop Start Line PBX
Outgoing
Loop Start Line PBX
Incoming
Seize Tip-Ring leads activated
(shorted); Loop Current flows
in line 90Vac is applied to Ring
lead in 2 sec on, 4 sec
off cadence
Seize
Acknowledgment Loop Current and/or dial tone
generated —
Digits Loop Current toggled (Rotary)
or DTMF —
Stop Dial — —
Receipt of Digits Audible Tones - Busy,
Reorder, Ringback dependent
upon digits dialed and called
party condition —
Answer Supervision Some COs can reverse
current flow
Tip-Ring leads activated
(shorted); Loop Current
flows in line
Disconnect
Supervision Near- end termination: PBX/
Telephone can break Loop
Current Near- end termination:
PBX/Telephone can
break Loop Current