JRC JRL-2000F Service Manual page 9

to turn on the transistor TR3 and the eooling fan starts to rotate. ·
When the temperature of the heat sink exeeeds 80
oc,
the eomparator IC6 (2/4) or
IC6(4/4) turns on.
At this time a Low Ievei PA HEAT alarm signai is sent to the CDJ-1143eontrol eireuit
via diode CD?.
When the PA HEAT alarm is issued, the JRL-2000F displays "A3".
4)PA UNBL Alarm Deteetor Cireuit
The CFF-361 power eombiner is equipped with a sensor R7 whieh deteets unbalaneed
power when the power is eombined.
This sensor deteets the unbalaneed power and when the terminal valtage of the sen-
sor inereases, the eomparator IC1 (2/4) turns on, and the PA BL alarm signal is gener-
ated.
When the PA BL alarm is issued, the JRL-2000F displays "A4".
S)PA LOAD Alarm Deteetor Cireuit.
The CFF-361 power eombiner is equipped with a cireuit whieh deteets Vf and Vr of
the PA output terminal.
Vf and Vr are eompared by the eomparator IC2 (2/4).
When the VSWR value exeeeds 3.0 at the PA outputterminal beeause of a poor
matehing situation with the matehing eireuit, the ratio VrNf exeeeds 0.5 and the eom-
parator IC2 (2/4) ehanges from Low Ievei to High Ievei.
This eomparator output signal triggers the flip-flop cireuit eomposed of IC2 (3/4) and
IC2 (4/4), and turns over the output voltage to issue the PA LOADalarm signal.
When the PA LOADalarm is issued, the JRL-2000F displays "A9",
IC2 (1 /4) and the peripheral deviees eompose of a cireuit whieh resets the flip-flop.
6)PA OFF Cireuit
When one of the three alarm signals of the PA eontrol beeomes Low Ievei, or when
PA OFFsignal whieh foreedly turns off the power amplifier beeomes Low Ievei be-
eause of the operation of the other proteetion eireuit, a Low Ievei signal is sent to the
· inputterminal of the eomparator IC1 (4/4) via CD4 or CD6 diode OR eireuit and the
output of IC1 (1/4) turns from Low Ievei to High Ievei. '
This signal is applied to the DC amplifier whieh eontrols the bias voltage of the power
amplifiers IC3 (3/4) and IC3 (4/4), and the bias voltage of the power amplifiers is set to
-9V.
lf the bias voltage beeomes -9V, the RF power MOSFET of the power amplifier is eut
off and the output power beeomes 0 W, regardless of the existenee of the exeitation
power.
8
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