6-24 888-2408-002
WARNING: Disconnect primary power prior to servicing.
Troubleshooting
6.11.6 A or B#_OT, PA Over-Temperature
The temperature of each PA is sensed by thermistor, RT1 (located on each
individual amplifier board). If the temperature reaches 100°C, the transmitter will
mute and disconnect the problem PA via the isolation switch. If one of the
thermistors or its wiring is shorted the temperature indication will be 155°C.
6.11.7 A or B#_OUT, PA Out Fault
This is the interlock fault for each PA. Two of the edge connector contacts on each
PA, J1-A and J1-V, are shorter than the others. They will not make contact unless
the PA is fully engaged in the Z Plane connector. If the PA is not inserted, these two
contacts are open and the controller will disconnect the PA from the system and
report the fault in the Fault Log as A#_OUT or B#_OUT (where # is a number from
1-8). This information also shows up in the Diagnostics Display “Status Menus”
under PA Status. To check the status of each PA press [STATUS C, then C or D to
check Z Plane A or B].
6.11.8 A or B#_ISO, PA ISO Temperature Fault
The fault threshold for the PA Isolation load resistors is 150°C. These resistors are
located on the Isolation Boards mounted on each side of the PA. Normally the ISO
resistors have minimal current flow through them and run about 40-100°C. If the
amplifier connected to the ISO resistor has a difference in phasing or amplitude
compared to the other three amplifiers in its foursome, then the resistor will try to
absorb the imbalance, increasing its temperature. The bigger the imbalance the
faster the temperature rises. Each resistor has a thermistor attached to it with a
special epoxy to sense the resistor temperature. When 150°C is exceeded (or
predicted to do so), the fault log will register an A#_ISO or B#_ISO fault (where #
is a number from 1-8), the transmitter will be muted for 120mS, the problem PA will
be switched out and the mute released. This overload is actually a predicted
overload based on the measured temperature rise in the ISO load over a given
amount of time. This means the ISO resistor will not actually get to 150°C before
the system trips, but that the system will switch out the problem PA if that
temperature would have occurred based on the ISO resistor rate of temperature rise.
To monitor the ISO resistor temperatures on the Diagnostics Display by Z-Plane
press [METERING C,C].
NOTE:
The individual PA ISO resistor temperatures can vary quite a bit but are to be
considered okay if they are under ambient temperature + 75°C. For example,
with an ambient temperature of 25°C the PA ISO temperatures are okay if
they are under 100°C (25°C + 75°C).
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