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SX-200 ICP MX Technician’s Handbook
Test/Verify (Ground Start)
• Verify the far-end (CO) circuits by using a standard telephone for
incoming calls. Verify outgoing calls by using a Butt Set with a ground-
start lead (momentarily shorting the ring lead to the ground will
produce a dial tone from the far end).
• Verify the near-end (PBX Ground Start) circuits by connecting to
known working far end Ground Start circuits.
• Verify that appropriate voltages are present on Tip-Ring in each call
state.
• During off-hook condition, 18 mA DC minimum should be drawn from
the CO (typical 35-40 mA).
• Tip-Ring is polarity sensitive. PBX will be unable to initiate calls if
reversed. Reverse polarity to verify.
Table 51: Ground Start Trunk Summary
Signal
Ground Start Trunk PBX
Outgoing
Ground Start Trunk
PBX Incoming
Seize Ring lead goes active. PBX
grounds the ring lead
Tip lead goes active; 90
Vac is applied to Ring
lead in 2 sec on, 4 sec off
cadence
Seize
Acknowledgment
Tip lead goes active; Audible
Dial Tone generated; ground
returned on tip
Tip-Ring leads activated
(shorted); Loop Current
flows in line
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
CO reverses current flow in
Tip-Ring
—
Disconnect
Supervision
Near-end: PBX opens loop
Far-end: CO removes ground
from ring
Near or Far-end
termination: Loop
Current is broken