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HARRIS
888-9058-001
WARNING: Disconnect and lockout AC primary power prior to servicing
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If open pass FETs are suspected check the voltage at collector (case) of Q1 of the
Module Control Board as the module is enabled and disabled. This voltage is fed
through resistance to the gate of the pass FETs. When Q1 collector is high (enabled),
+50 Volts should appear at the quarter modules. When Q1 collector is low (disabled),
no voltage should be present at the quarter modules.
If a fault is suspected in the gate voltage circuit, trace signals back through CR4, R58,
and C9 to the oscillator U4. Pin 7 should show a triangle wave with peaks at 0 and +15
Volts. Buffer U7 pin 14 should be low if enabled. PAL U1 pin 12 should be low if
enabled, and +5 Volts if disabled.
8.3.4 Isolating Other Failures
This section includes troubleshooting procedures for situations where a problem is not
indicated as a fault by the module logic and control circuit, and no blink code is given.
Amplifier Module Will Not Enable, Has 50 Volts Applied To It But No LEDs Will
Light:
The cause could be a loss of the 15 Volt DC supply in the module. Check the
following:
If fuse F1 on the module control board is open, check for a short circuit on the 15 Volt
line after the 15 Volt regulator.
If resistor R80 on the module control board is open, look at the 15 Volt regulator U11
itself. The regulators tab is internally connected to its output, and thus must be isolated
from the chassis. Use an ohmmeter to check whether the regulator tab has shorted to the
chassis.
Amplifier Module Will Not Enable, Has a Steady Red LED Illuminated and Will
Not Change to the Green LED Illuminated:
A possible cause could be that the module
control board is not receiving the enable command from the slave controller. Try
enabling the module on the bench or on extender, or try the swap test after reading the
precautions in section A.3.2. If the module now enables, use a multimeter to check the
enable wiring in the transmitter cabinet.
If the module still does not enable while in a different cabinet slot, check the continuity
of the yellow enable wire inside the module. This wire runs from the black plastic
power connector on the module rear panel to a feedthrough capacitor, then to J1-12 on
the module control board. If this wire is intact, then the module control board is
probably defective. The module is normally enabled by grounding this control line.
Module Has Only 1/2 Green LED Illuminated and Low or No RF Output:
The
module has been enabled but little or no RF drive has been applied to the quarter
modules. This indication is given only in PA modules; drivers have both green LEDs on
during an enable condition, regardless of drive level. This indication is sometimes a
normal condition in PA modules used in the drive chain of a transmitter whose output
power is significantly below 30kW.