Comark IOX Series Technical Service Bulletin

This service bulletin provides a troubleshooting table for the Comark IOX and DCX series of
UHF television transmitter. The information contained in this table is the compilation of inputs
from Comark customer service representatives, field service engineers, design engineers, and
customers. If you would like to make an addition or correction to this table, please send your
information to the Comark Customer Service department via e-mail to
csfeedback@comarktv.com
Symptom
"Soft Start" failure prevents
application of high voltage.
Beam voltage OK when HV is
isolated, but sags significantly
(>5kV) when IOT is
connected. Possible positive
grid current alarms or severe
distortion of transmitted
waveform.
Beam voltage is 2/3 of
nominal value e.g. 22kV
instead of 33kV.
Beam voltage is unstable, bi-
stable (jumping between two
values).
Beam will not come on due to
cabinet interlock alarm, yet all
safety devices connected to
cabinet interlock line are in
proper positions.
High voltage is stable in beam
mode but drops out with
cabinet interlock alarm after
REV H - 10 January 2007
Technical Service Bulletin 030328
IOX / DCX Troubleshooting Table
Problem / Solution
480VAC Three Phase Power
Missing phase in 480V feed to beam supply primary. Trace three-phase voltages back from
beam supply disconnect with voltmeter to find where missing leg disappears.
Possible partial failure of CB3 motorized breaker. Check for presence of three-phase 480V
at output terminals of CB3 when closed. Replace CB3 as necessary.
Possible failure of HV rotary switch or outdoor disconnect. Check for 480V at output
terminals of suspected device. Replace faulty components as necessary.
To prevent damage to CB3 breaker, HV rotary switch, step-start contactors, and other 480V
devices, check tightness of terminal connections at regular intervals as part of a
preventative maintenance program.
Missing phase in 480V feed to beam supply primary. Trace three-phase voltages back from
beam supply disconnect with voltmeter to find where missing leg disappears.
Possible partial failure of CB3 motorized breaker. Check for presence of three-phase 480V
at output terminals of CB3 when closed. Replace CB3 as necessary.
Possible failure of HV rotary switch or outdoor disconnect. Check for 480V at output
terminals of suspected device. Replace faulty components as necessary.
Missing phase in 480V feed to beam supply primary. Trace three-phase voltages back from
beam supply disconnect with voltmeter to find where missing leg disappears.
Possible partial failure of CB3 motorized breaker. Check for presence of three-phase 480V
at output terminals of CB3 when closed. Replace CB3 as necessary.
Possible failure of HV rotary switch or outdoor disconnect. Check for 480V at output
terminals of suspected device. Replace faulty components as necessary.
Possible high voltage breakdown of 60 ohm filter resistors in HV beam supply. Extinguish
high voltage and inspect beam supply resistors. Replace resistors as necessary.
Possible over-temperature condition in step-start resistors. Step start resistor temperature
sensor is also part of cabinet interlock line. Condition typically occurs after frequent HV on-
off cycles in a short period of time. Allow step start resistors to cool down for ten minutes.
Interlock will clear itself as resistors cool.
Step-start overheating may also be due to open phase leg on K32 step start contactor.
Remove 480V and connect voltmeter across contactor terminals for one phase. Reapply
480V and read voltage drop across contactor while engaged. Repeat measurement for all
three phases. Look for non-zero voltage drop on one phase leg. Replace K32 as necessary.
Note: other devices in cabinet interlock line are HVPS door, HVPS ground hook, HVPS oil
level switch, HV key interlock system.
Possible over-temperature condition in step start resistors due to high resistance condition
in one or more legs of K32 step start contactor. Step start resistor temperature sensor is
also part of cabinet interlock line. Remove 480V and connect voltmeter across contactor
Technical Service Bulletin 030328
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