3-20 Troubleshooting
3.3.4.2 Troubleshooting Details
Prior to any detailed troubleshooting, once the cover is off, it is suggested to inspect all of the circuit
boards of the PA to look for evidence of damage. This may include loose components, charred PCB/
components, black residue surrounding components or black residue on inside of cover. This may
help to guide you to the problematic area, or indicate a secondary failure mode that may have
resulted but was not diagnosed.
The details below will indicate when DC and/or RF power is to be applied. It should be assumed that
no DC or RF power is to be applied until stated.
PA circuitry is grounded to the PA cast heat sink, and measurement equipment should be connected
to the same ground when performing any testing of the PA.
3.3.4.2.1 Troubleshooting the Fan Switch
1. Disconnect the fan connector from the feed-through capacitor on the fin side of the PA
heat sink.
2. Check for DC continuity through feed-through capacitor to determine if component
failure has occurred, and replace if necessary. Severe electrical or mechanical stress
could result in failure of this component.
3. Verify resistance of R6595 (if placed), R6596, and R6597 to determine if component
failure has occurred, and replace if necessary. A fan failure could result in over-
dissipation of these resistors.
4. Apply 28.6 V and 14.2 V DC power to the PA. Measure pin 3 of Q6590, and it should be
approximately equal to the 14.2 V input voltage to the PA (pins 1 and 4 of J6001). If not,
something between these points is disconnected. If it is, then the only way to force the
fan to turn on is to use the mule base station/repeater, and it will attempt to turn on the
fan on upon the base station/repeater boot up for a diagnostic test, at which point pin 4
of Q6590 should be approximately equal to pin 3.
5. When the fan circuit is energized during the fan test during the base station/repeater
boot up, the voltage drop across resistor R6596 should be approximately 2 V. If it is
significantly more or less than this, this indicates abnormal current draw of the fan, and
the fan should be replaced.
6. If no specific failure is found, replace the fan and/or distribution board. Recalibration and
retest is required, if the distribution board is replaced.
Technicians troubleshooting and repairing the circuit boards
must be trained, and capable of removing and replacing
surface-mount components of the appropriate package sizes.
Failure to properly install/replace any component may result
in failure and/or reduced reliability.
The PA will require recalibration if the Output Board is
replaced. Recalibration is not necessary if the RF Board is
replaced. If recalibration is not possible but is required, the PA
module will need to be replaced.
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