operating voltage in case of a high voltage
transient coming in the AC power line.
It is recommended that spare MOV’sof
the appropriate size be carried asspare parts
for each transmitter. If severe transient con-
ditionsexiston thepowerlineand theMOV
fails frequently other transient suppression
means should be utilized to eliminate this
problem.
The three phase input to the transmitter in
the standard GATES FIVE is monitored for
correct phase and amplitude. This helps to
protect the three phase transformer from
damage due to a severe phaseimbalance (or
loss). This detector monitors all three lines
of AC and provides a contact closure when
the AC is correctfor operation.This contact
closure is wired in series with the cabinet
interlock.
The negative side of the high voltage
power supply is returned to cabinet ground
through a shunt resistor A19R7 which is
used to measure power supply current.
The positive voltage is applied to the PA
modules via connections at the PA Current
shunt A19R6.
The supply voltage is set by the primary
taps of A19T1 to allow line voltage adjust-
ment from 197 volts to 251 volts with 11
volt steps.
During the turn on sequence resistors are
connected in series with the primary of the
highvoltagetransformerto limit thecapaci-
tor charging current to a safe value. When
the primary voltage builds up to a near
normal level, the Run contactor, K2, closes
and allows full voltage to be applied to the
primary of the transformer.
5.3.10. Low Voltage Power Supply and
IPA Power Supply
5.3.10.1. Introduction
The purpose of the low voltage power
supply is to provide a +/-20 volts supply for
all control and driver functions in the trans-
mitter. The LowVoltage Supplyis not regu-
lated, however individual boards that
require regulation will do on-board regula-
tion for 15 and 12 volt applications. The
Low Voltage Supply provides 60 to 120
VDC to the IPA module.
5.3.10.2. Description
The IPA and +/-20 volt power supply
transformer is A20T1.Ithas 208/240inputs
plus taps for +/-11 volt variations to com-
pensate for AC line variations. The low
voltage secondary ofthe transformeris cen-
ter tapped with two MOV’s(MetalOxide
Varistor) across the secondary terminalsfor
transient protection the same as on the high
voltage power supply.
The center tap of the low voltage secon-
dary is grounded and full wave rectifier
diodes rectify each half of the secondary
voltage to produce +20 volts at 2 amps
maximum and -20 volts at 2 amps maxi-
mum.
The IPA portionof A20T1 secondarycon-
sists of a common tap plus 5 tapsto provide
a range of voltages to control the proper RF
drive level to the PA modules.
The low voltage power supply is not
step/started and is on whenever AC power
is applied to the transmitter. If the circuit
breaker in the base of the cabinet is ON the
pilot light on the front panel in the base of
the cabinet will be illuminated.
Since this is a low voltage power supply,
there are no interlocks on the rear panel
controlling this power supply.
5.3.11. Airflow Sensor
5.3.11.1. Introduction
An air flow sensor circuit, located in the
air inlet for both fans, provides protection
against a fan failure by sensing wind chill.
If a fan fails, the lack of wind chill is de-
tected, and the transmitter shuts down. An
audible alarm sounds to signify a fan fail-
ure.
5.3.11.2. Description
The function of the Air Flow sensor is
based on a comparison of voltage outputs
from individual temperature sensing de-
vices. One sensingdevice (U3) is unheated,
such that it samples the ambient tempera-
ture. There are two other sensors (U2 and
U4); one for each fan, and they are heated
by resistors R2 and R1, respectively.
If a fan stops running, the corresponding
heated sensor increases in temperature,
whereas the ambient sensor is unaffected.
As the heated sensor increases in tempera-
ture, the voltage difference climbs. When
the pre-determined threshold is crossed,
comparator U1 triggers, and closes the on-
board relay, K1. Contacts of this relay in-
terrupt the contactor coil circuit (K1 in the
AC drawer). At the same time, the relay
provides voltage to the audible warning de-
vice and the red led, DS1. Also, the status
of the remote contacts change position.
As soon as relay K1 closes, power for the
heated sensors is removed. This allows
them to cool down so that you may restart
the transmitter.
5-6 888-2314-001 Rev. T: Jan. 1996
WARNING: Disconnect primary power prior to servicing.
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