Harris Platinum HT EL 2000LS, Technical Manual

Page: 76 / 90

supply pins and the wiring to its slot. If no problem is found in
the power supply or connections, then the problem could be on
the control board, either in the control logic or the comparator
thresholds. See the procedure for checking for correct Over/Un-
der Voltage Fault Threshold located on page A-17 in this section.
Over Temperature Fault (5 blinks) — The module can be
damaged if it is not cooled properly while operating. To protect
the amplifier, each quarter module has a temperature sensing
circuit that signals the control board to disable the power ampli-
fier if the temperature of any quarter module temperature exceeds
80
o
C. When this occurs, the logic disables the module, and
commands the red LED to blink five times.
First, check the cabinet air filters and module heatsink for accu-
mulated dust. Verify that the cabinet air plenum is providing
proper air flow to the module slot. Measure the air inlet tempera-
ture, it should be below the maximum temperature rating of 50C.
If the temperture is more than a few degrees above outside
temperature, the air supply system may not be adequate. If an
improper module fault is is suspected, allow the module to cool
for a time, then try the following: 50 Volts to the module
and, without enabling it, check the voltages at test point TP-1 on
each quarter module center board. This voltage represents the
temperature of the heatsink at the location of the temperature
sensor. The voltage is calibrated to be 2.30 Volts at a temperature
of 25
o
C. The calibration control is R2 on each quarter module
board. The voltage at TP1 is compared against a reference voltage
of 5.82 Volts generated by a voltage divider.
Measure the quarter module temperature reporting inputs at U13
pins 5,7,9, and 11. If any quarter module input is lower than the
reference check for an overheated quarter module, an incomplete
temperature reporting circuit, or failure of a quarter module bias
and temperature reporting circuit. If the reference voltage is
lower than all the temperature reporting lines, the outputs of U13
should be high, and the output of U5 should be low, and the
module should not be reporting a temperature fault. If a tempera-
ture fault is reported check for proper operation of comparator
U 1 3 , S c h m i t t t r i g g e r U 5 , o r p o s s i b l e PA L fa i l u re.
Pass FET Failure Fault (6 blinks) — Should one of the pass
FET DC switch transistors fail to a shorted condition, the control
board will sense it and blink the red LED six times. The pass
FETs are 60 amp 100 Volt MOSFETs used as DC switches to
enable and disable the module as necessary by applying or
removing DC from the quarter modules.
CAUTION
IF A PASS-FET FAILURE IS INDICATED, THE MODULE CANNOT
BE TURNED OFF EXCEPT BY TURNING OFF THE PA CABINET
OR BY DISABLING THE POWER SUPPLY WHICH POWERS THE PA.
A MODULE INDICATING PASS-FET FAILURE SHOULD NOT BE
REMOVED FOR SERVICE WITH POWER APPLIED, AS COMPO-
NENT DAMAGE COULD RESULT.
A shorted pass FET (drain-source short) is normally confirmed
by measuring the resistance from the red 50 Volt wire of any
quarter module to the +50 Volt pins of the input connector with
an ohmmeter.
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 col-
lector 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.
A.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 LED’s 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 regulator’s 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 Illumi-
nated — 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 will 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 indi-
cation is sometimes a normal condition in PA modules used in
the drive chain of a transmitter whose output power is signifi-
cantly below 30 kW.
If this is not the case, then the cause for loss of drive could be
either in the module or in the transmitter cabinet. First, check for
normal exciter and transmitter output levels.
Platinum™ Series
A-10 888-2457-001
WARNING: Disconnect primary power prior to servcing.