Ericsson 19A704647P1, Руководство по обслуживанию

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OVERTEMPERATURE PROTECTION
In order to protect the supply from abnormal ambient
temperature operating conditions or prolonged radio transmis-
sion, overtemperature protection was added to the supply. A
thermostat, S2, is attached to the heatsink of the supply to
monitor the operating temperature of the series pass transis-
tors. This thermostat is a normally closed switch type. When
too high an operating temperature is reached, the thermostat’s
contacts open, thus removing the AC line voltage to the supply.
When the temperature of the heatsink returns to a safe value,
the contacts of S2 close and operation is automatically re-
sumed.
OUTPUT OVERVOLTAGE PROTECTION
To protect the power supply load from possible overvol-
tage conditions due to failure of the control circuitry, an
overvoltage sensing and shutdown circuit has been included.
This circuit is composed of VR1, VR2, C8, R10, R11, R12,
Q4, and U1. When the output voltage exceeds 15 VDC, VR1
reaches its ZENER voltage and begins to conduct current.
This current develops a voltage across R12, which then trig-
gers thyristor Q4 into forward conduction. With Q4 turned
ON, a portion of the bias voltage is applied directly to the
shutdown pin of U1. With pin 8 of U1 held high, the drive to
Q3 is disabled, thus turning off the output voltage. Thyristor
Q4 remains ON until AC input power is removed. The re-
moval of AC input power interrupts the holding current
through Q4 and turns it off. Therefore, in the event of an
overvoltage shutdown, the power supply remains OFF
until the AC input power is removed and then restored either
via the main power switch, or disconnection of the AC line
cord.
INTERNAL BIAS VOLTAGE SUPPLY
Internal bias voltage to the power supply is provided by a
separate winding on transformer T1. AC input power is trans-
formed via this winding at J6 and J7 along with D2 and C9
into approximately 30 volts DC at nominal line voltage. This
bias voltage then provides power to all to the internal circuitry
of the supply.
OPERATION
1. Connect 13 Vdc output to the load using the mating
connector.
2. With the ON/OFF switch in the OFF position, con-
nect the AC power cord to a 120V power source for
parts 1, 2, 11, & 12.
For parts 3 and 14 a connector (customer supplied)
must be installed on the power cord for connections
to a 240V power source.
3. Place the ON/OFF switch to the ON position to turn
on the supply.
MAINTENANCE
For disassembly, remove 4 screws and lift off top cover.
When replacing any component be certain to use an identical
component. When replacing the thermostat mounted on the
heatsink, apply thermal compound between the two. Observe
wire routing when resoldering circuits. Failure to do so may
lead to excessive ripple or poor regulation.
TROUBLESHOOTING
When troubleshooting is required, use the guides given in
the following table to analyze defects. When a component or
assembly has been identified as defective, replace the defective
component and also check the associated components before
applying power to the unit in the event that a series of compo-
nents are defective.
When replacing any component be certain to use an iden-
tical component. When replacing the thermostat mounted on
the heatsink, apply thermal compound between the two. Ob-
serve wire routing when resoldering circuits. Failure to do so
may lead to excessive ripple or poor regulation.
Recommended test equipment for maintenance or trou-
bleshooting of this power supply includes:
•
Digital multimeter
•
50 amp DC meter
•
Resistive load
•
Oscilloscope
This unit contains dangerous voltage levels. It is
strongly recommended that defective units be
returned to the manufacturer for repairs.
If field repairs are necessary, remove input power
and then use a load resistor to manually discharge
each capacitor before working on the circuits.
WARNING
LBI-38751
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