Comdial DX-80 Technical Manual page 73

Symptom(s)
(Continued)
Telephone/ CPU Heartbeat
Terminal apparatus LED flashing
dead and 408M/
408E/DPM8
module
Heartbeat
flashing but
one or more
digital
telephones are
not
functioning.
Note: Digital telephones use only one twisted cable pair for power, data control and voice com-
munications. There are no fuses for station interface protection. Instead, a current sensing
Polly-switch limits excessive current going to each terminal connection. If a station cable pair is
shorted or a telephone's DC power supply is damaged, the Polly-switch will temporarily open to
protect the KSU Module circuitry.
Digital telephone Digital Volt/
erratic operation: Ohm Meter
- Erratic LED/LCD
operation
- Faint data noise in
the background
during
conversations
October, '03
Diagnostic Cause(s)
Aid
Shorted station
cabling.
Bad Telephone
Cable distance
is too long for
gauge of wire/
cable used.
Non-standard
telephone
cable being
used.
Multiple
digital
extensions
being fed from
one common
cable or on the
same cable
pair.
Comdial
DX-80 Installation & Maintenance
Action
At the KSU, power the system down and
remove the power cord from the AC outlet.
Remove the KSU cover (four screws).
Disconnect all station wiring on the affected
408M, 408E, or DPM8 and connect one
known-good DET directly to one of the
interface ports. Replace the KSU cover and
retest with this phone. If this telephone works
OK, follow the above procedures to test each
interface port. If any port is found bad replace
the module. If no port is found bad, replace the
wiring/cabling.
If the above test yields all working ports and
no cabling errors, test each connected
telephone one at a time until the bad telephone
is discovered. Replace the telephone.
If a digital telephone is not receiving clear
2B+D signaling from the KSU, test as follows:
1. With station cable cross-connect (jumper)
wire removed and telephone unplugged, place
a short circuit across the inside wiring cable
pair at the user end (jack) of the cable.
2. With a DVM, measure the short circuit
resistance one way. The short-circuited cable
pair ohm reading should not exceed ____
ohms.
Each digital telephone should operate on one
dedicated, unshielded, twisted pair cable to
avoid data noise and interference between
adjacent cable pairs.
73