Mitel Sx 200 El/ml Technicians Handbook

Troubleshooting and Repair
71
Troubleshooting
Loop Start Line/Trunk
The Loop Start Line/Trunk serves the standard domestic applications 
and small businesses that have key systems and PBX applications. 
Figure 13:  Loop Start Line/Trunk
Table 6:  Loop Start Line/Trunk Summary
SignalLoop Start Line PBX 
OutgoingLoop Start Line PBX 
Incoming
SeizeTip-Ring leads activated 
(shorted); Loop Current flows 
in line90Vac is applied to Ring 
lead in 2 sec on, 4 sec 
off cadence
Seize 
AcknowledgmentLoop Current...

Technician’s Handbook
72
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.
Receipt of DigitsAudible Tones -...

Troubleshooting and Repair
73
Troubleshooting
Ground Start Trunk
The Ground Start Trunk serves most PBX-CO connections in an analog 
environment.
Figure 14:  Ground Start Trunk
Table 7:  Ground Start Trunk Summary
SignalGround Start Trunk PBX 
OutgoingGround Start Trunk 
PBX Incoming
SeizeRing lead goes active. PBX 
grounds the ring leadTip lead goes active; 90 
Vac is applied to Ring 
lead in 2 sec on, 4 sec off 
cadence
Seize 
AcknowledgmentTip lead goes active; Audible 
Dial Tone generated; ground...

Technician’s Handbook
74
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...

Troubleshooting and Repair
75
Troubleshooting
Direct Inward Dial (DID)/Loop Trunk 
You use the Direct Inward Dial (DID)/Loop trunk primarily in analog DID 
applications; rarely in PBX-PBX Loop Tie trunk applications.
This trunk uses current reversal to signal supervision information and 
provides digit flow capability in both directions, when the trunk is in the 
loop/tie mode.
Figure 15:  Direct Inward Dial (DID)/Loop Trunk 

Technician’s Handbook
76
Table 8:  Direct Inward Dial/Loop Trunk Summary
SignalDID/Loop Trunk PBX 
OutgoingDID/Loop Trunk PBX 
Incoming
SeizeTip-Ring leads are activated 
(shorted); Loop Current flows 
in lineTip-Ring leads are 
activated (shorted); Loop 
Current flows in line
Seize 
AcknowledgmentImmediate Dial - Tip-Ring 
leads stay active
Outgoing Wink - Tip-Ring 
leads toggle 
Loop Current direction Delay 
Dial - Tip-Ring leads reverse 
Loop Current following 
seizure; reverse again when 
ready to...

Troubleshooting and Repair
77
Troubleshooting
Test/Verify (DID)
Verify the far-end circuits by the use of a standard telephone for 
outgoing calls.
Verify the near-end circuits by connecting to known working DID/Loop 
circuits.
Verify that appropriate voltages are present on Tip-Ring in each call 
state.
During off-hook condition, 20-25 mA should be drawn from the far-end.
Ear & Mouth (E&M) Trunk
You use the E&M trunk in Tie Trunk applications. The E&M trunks 
support all the signaling information.
The...

Technician’s Handbook
78
Figure 16:  E&M Trunk - Type I (2-wire) 

Troubleshooting and Repair
79
Troubleshooting
Type V
Type V is used in applications where short distance direct back-to-back 
operation is desired. The M-lead invert is required at both ends. 
Figure 17:  E&M Trunk - Type V (4-wire)
Table 9:  E&M Trunk Summary
SignalE&M Trunk PBX 
OutgoingE&M Trunk PBX 
Incoming
SeizeM lead goes active (voltage 
is dependent on Type I or 
Type V operation)E lead goes active
Seize 
AcknowledgmentImmediate Dial - E Lead 
stays idle. Outgoing Wink - 
E Lead toggles...

Technician’s Handbook
80
Test/Verify (E&M)
Loop back to self whenever more than 1 E&M type V circuit is available.
Verify far-end circuits by activating near-end M lead and listening for far- 
end dial tone.
Verify near-end circuits by activating near-end E lead and listening for 
near-end dial tone.
Verify that appropriate voltages are present on E&M leads in each call 
state.
DigitsM toggles (Rotary) or DTMF 
through audio pathE toggles (Rotary) or DTMF 
through audio path
Stop DialE lead goes active;...