Abell A-82 - Power Supply System; Control System Overview

ABELL A-82 UHF Service Manual
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6） Antenna converting switch and LPF
Before the RF signal arrive the Antenna terminal, the signal from RF amplifier go through a lowpass
filter and transmit/receive converting circuit. Transmit/Receive converting circuit is made up by D200,
D301 and D302. D200, D301 and D302 are open in the transmit mode, and shut down in the receive
mode.
7） Power Control
Power control circuit, stabilize the transmiting output power by AGC(Auto-control gain cuicuit). Voltage
comparing circuit, IC201(2/2) compare the voltage obtained from the final current by the reference
voltage set by microprocessor. The power control voltage is in direct ratio to the difference value
between the reference voltage and auto-detecting voltage from IC 201(1/2). The output voltage control
the field-effect tube amplifier, keep the output power constant. Transmit output power can be adjusted
by CPU, change the output power by modify of reference voltage through CPU.
8） Temperature protecting circuit
When the temperature of thermistance is up to 80 , protecting circuit will enable Q209 to protect final 
amplifier Q203 from overheating.
5．Power supply
The 5V pwer of CPU(5C) is provided by inputing 7.5V to A15, low level output by CPU(IC1 Pin15)
close Q15 to provide 5V power. In normal work mode, CPU(IC1 Pin33) output high level, contol Q18
provide 5V power for PLC. In transmiting mode, CPU(IC1 Pin34) output high level, control Q18 provide
5V power for TXC, in receiving mode, CPU(IC1 Pin35) output low level, control Q10 provide 5V power
for RXC.
6．Control system
The IC1 CPU operates at 9.8304MHz