Ericsson 19D901841G2, Maintenance Manual

Page: 2 / 10

A directional coupler, W19, and detector CR1 provide a
voltage, proportional to the power out, to the power control.
POWER CONTROL
On the Power Control Board, the voltage from the detector
is compared to a stable DC reference voltage in a high gain
comparator, U2A. The comparator drives a DC amplifier, Q4
and pass transistor Q6 that supplies control voltage to the RF
board.
Thermistor RT1 is connected to the PA heatsink and, by
controlling the operation of Q2 and Q3, provides a power
cut-back for ambient temperatures that exceed 70 degrees
centigrade. Conduction of Q3 gradually decreases the power
set voltage applied to Q4. The DC reference voltage is provided
by Q1, U3, R17-19, and C5.
In other special applications of this power control board,
U2-B, CR1, and Q5 provide a low power alarm. U1 is used to
select one of four individually adjustable power levels.
R1, R4, R7, and R10 are factory adjusted values.
Copyright© August 1987, General Electric Company
This amplifier is not field repairable. Should service
become necessary, the complete power amplifier
assembly must be returned to the factory for servicing.
NOTE
The RF Power Transistors used in the transmitter contain
Beryllium Oxide, a TOXIC substance. If the ceramic, or
other encapsulation is opened, crushed, broken, or
abraded, the dust may be hazardous if inhaled. Use care
in replacing transistors of this type.
WARNING
LBI-38134 LBI-38134
1