Ericsson GE MASTR II 19A149979P1, Maintenance Manual

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tors. C9 serves as a resonating capacitor across the secon-
dary taps of the transformer.
The transformer steps the input voltage down to ap-
proximately 28 Vac across two secondary windings. Each
winding drives two separate full wave bridge rectifiers con-
sisting of D1A, B through D4A, B. The rectifiers are dual
diode packages and are mounted on heat sink HS 1. During
the first half of the period diodes D1B, D2A, D3B, and D4A
are conducting and delivering current which is summed at
the input to the high current filter. During the second half of
the period diodes D1A, D2B, D3A, and D4B are conducting
and also delivering current which is summed at the input to
the high current filter. The high current filter consists of C1-
C4, C7, L1, and R1. It is designed to reduce the output rip-
ple to less than 100 mV p-p for any current load up to 15
amps. It also keeps transient responses greater than 22 volts
and less than 30 volts. Resistor R1 is a 30 ohm, 50 watt re-
sistor that serves two functions. One, it acts as a bleeder re-
sistor to discharge the capacitors when the supply is turned
off. Two, it provides a minimum current load to prevent the
output voltage from ever rising above 30 volts under any
load condition. The high current filter sources up to 15 amps
through the 20 amp fuse F2 to the high current output port
F801A on the rear wall of the chassis. F801A-1 and F801A-
2 are A + and A-, respectively, and connect to the transmitter
power amplifier.
The two secondary windings are also center tapped to
produce a step-down voltage of around 14 Vac which is also
fed to the two full wave bridge rectifiers. During the first
half of the period, diodes D2A and D4A provide a conduc-
tion path for current going to both the high current filter and
the low current filter. During the second half of the period,
diodes D1A and D3A provide the conduction path for cur-
rent going to the high current filter and the low current fil-
ter. The low current filter consists of C5, C6, L2, and R2. It
is designed to reduce the output ripple to less than 100 mV
p-p for any current load up to 3 amps. It also keeps transient
responses greater than 11 volts and less than 18 volts. Resis-
tor R2 is a 100 ohm, 10 watt resistor that serves two func-
tions. One, it acts as a bleeder resistor to discharge the
capacitors when the supply is turned off. Two, it provides a
minimum current load to prevent the output voltage from
ever rising above 18 volts under any load condition. The
low current filter sources up to 3 amps through the 5 amp
fuse F3 to the low current output port J801 on the rear wall
of the chassis. J801-1, 2, 3 and J801-4,5,6 are A+ and A-,
respectively, and connect to the receiver and system cir-
cuitry.
The power supply is rated for a nominal 26.0 Vdc for a
15 amp load out of F801A and for a nominal 13.0 Vdc for a
3 amp load out of J801 (receiving and transmitting simulta-
neously). When receiving only (a 3 amp load out of J801)
the output voltage is less than 15.8 Vdc at J801 and less
than 29.0 VDC at F801A.
MAINTENANCE
For disassembly, remove 8 screws and lift off top cover.
Disassembly is required before working on the power sup-
ply. When replacing any component be certain to use an
identical component. Thermal joint compound is required
between diodes D1, D2, D3, and D4 and the heat sink.
TROUBLE-SHOOTING
The trouble-shooting procedure in Table 1 may be help-
ful in isolating a defective component or assembly in a mal-
functioning power supply. When a component or assembly
is identified as defective, replace the defective component
with an identical component. Be sure to check associated
circuitry for any other damaged components before apply-
ing power to the unit.
ADJUSTMENTS
This power supply has no adjustments or controls other
than the ON/OFF switch.
INSTALLATION
The power supply is normally installed in an EIA 19
inch wide rack of a MII base station cabinet. It can also be
installed in a 19 inch wide stand alone open rack.
To avoid electrical shock, disconnect power supply
from the AC input power source before removing or
replacing any component or assembly.
WARNING
Insure that ventilation holes in the unit are not ob-
structed when the unit is mounted or in operation.
NOTE
LBI-38551
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