Circuit Analysis; 10-Volt Regulator Board 19C320918G1; System Board 19D429764G1 - Ericsson MASTR II Maintenance Manual

4. Turn the SQUELCH control R2401 clockwise (to the
right) as far as possible.
5. Adjust the VOLUME control R3 on the 19C320728
service speaker until the noise is easily heard in the
speaker but is not annoyingly loud.
6. Turn the SQUELCH control counter-clockwise (to the
left) until the noise just disappears, then advance the
control another 20 degrees.
MASTR II LOCAL CONTROL BASE
STATIONS
To adjust the VOL SET control R930 and the SQUELCH
control R2401, use the following procedure.
1. Apply a 1000 microvolt on-frequency signal modulated
by 1,000 Hz with ±3 kHz deviation to the Auxiliary Re-
ceiver Antenna Jack J2402.
2. Disconnect MASTR Local Controller cable from sta-
tion input (PI 102 from J1).
3. Connect an 8.0 ohm, 5-watt resistor across J2401-9 and
10, located at the rear of the Auxiliary Receiver.
4. Connect an AC vtvm across the 8.0 ohm resistor and
adjust R930 for a reading of 6.3-volts rms on the meter.
5. Disconnect the 8.0 ohm resistor and connect the con-
troller cable to the station. Disconnect the signal gener-
ator from J2402.
6. Turn the SQUELCH control (R2401) clockwise (to the
right) as far as possible.
7. Adjust the VOLUME control on the MASTR Local
Controller until the noise is easily heard in the control-
ler speaker but is not annoyingly loud.
8. Turn the SQUELCH control counter-clockwise (to the
left) until the noise just disappears, then advance the
control another 20 degrees.
LINE COMPENSATOR ADJUSTMENT,
R12, R19
Test Equipment Required
1. Signal Generator
2. Audio Oscillator
3. AC Voltmeter
Procedure
R12 in the line compensator is used to set the 3000 Hz
level. R19 is used to set the 300 Hz level. A Test Set-up Dia-
gram is shown in Figure 1.
1. At the Satellite Receiver, apply a 1000 millivolt, 1 kHz
signal with 3 kHz deviation from the signal generator
to the receiver as shown in Figure 1. Adjust LINE
OUTPUT potentiometer R936 on Auxiliary Receiver
System Board for a reading of 0 dBm.
2. Record this level as measured at telephone line input of
the voting selector, then remove the signal generator.
3. Connect the audio oscillator to the input of the line
compensator (Hole 14 on the Line Compensator Board
or J908 on the Auxiliary Receiver System Board). Set
the oscillator frequency to 1000 Hz, and adjust the level
to produce the same level recorded at the voting selec-
tor input in Step 2.
4. Record the output level of oscillator.
5. Change the oscillator frequency to 2800 Hz. Maintain
same oscillator output level as recorded in Step 4.
6. Adjust R12 on the line Compensator Board to produce
the same level recorded at the voting selector in Step 2.
7. Change the oscillator frequency to 300 Hz. Maintain
same oscillator level as recorded in Step 4.
8. Adjust R19 on line compensator to produce the same
phone line level at the voting selector as recorded in
Step 2.

CIRCUIT ANALYSIS

10-VOLT REGULATOR BOARD
19C320918G1
The hybrid integrated circuit U801 includes the 10-Volt
Regulator and regulator amplifier. Regulator pass transistor
Q801 is mounted to the heat sink located on the printed board.
The regulator circuit provides a closely controlled supply volt-
age for the receiver, Channel Guard and other options when
present. Input voltage (A+) for the regulator is supplied from
the station power supply via J2401-2 or some other external
source.
The Auxiliary Receiver ON/OFF switch S801 (located on
the Regulator Board) is normally left in the ON position. Turn-
Figure 1 - Test Set-up Diagram
ing on the station power supply applies voltage through
S801 and input filter C801-L801 to pin 1 of the regulator hy-
brid U801. The regulator amplifier output at pin 2 of U801 is
applied to the base of Q801, causing Q801 to conduct. The
voltage at pin 3 of U801 is the regulated 10-volts output. A
high impedance source at pin 5 of U801 provides a stable 5-
volt compensation input to the receiver ICOM.
Two LEDs are provided on the front panel of the Re-
ceiver. LED CR801 (ON) indicator is illuminated when
power is applied to the regulator and switch S801 is in the
ON position. When a signal is received, the received un-
squelch sensor (RUS) voltage developed by the receiver op-
erates the RUS switch Q909 on the System Board.
Conduction of Q909 operates Q802 on the regulator board.
Conduction of Q802 turns on LED CR802 (CARRIER AC-
TIVITY light).

SYSTEM BOARD 19D429764G1

The Auxiliary Receiver System Board contains the VOL
SET control R930, the de-emphasis and line driver circuits
for remote control applications, and jacks which accommo-
date the various options available. The System Board also
mates directly with the receiver modules through J903 and
J904.
VOLUME/SQUELCH HI from the receiver audio pre-
amp is connected via J904-11 to the VOL SET control R930
and SQUELCH control R2401. The VOL SET arm is re-
turned to the receiver IFAS Board where the audio is ampli-
fied by the receiver audio power amplifier circuit. The audio
output of the PA is then connected to the speaker leads at
J2401-9 and 10. The station VOL SET control is normally
adjusted for 5-watts output and the speaker level is control-
led by the MASTR Local Controller VOLUME control. In
multiple-receiver applications, the jumper between H1 and
H2 on the 19C320918 regulator board is removed, discon-
necting A+ from the receiver PA output transformer. This al-
LBI-30766
lows the audio to be applied to the Multiple Receiver PA and
speaker and limits the current drain requirements.
In MASTR II remote applications, the VOL/SQ HI is
coupled through the LINE DRIVER circuits to the remote
audio pair. The audio is connected through the high-pass fil-
ter consisting of C907-C908 and R901-R902. This filter at-
tenuates 60 and 120 Hertz to reduce the hum and noise. The
output of emitter-follower Q901 is passed through a de-em-
phasis network C909 and R906. This network provides a 6
dB/octave rolloff. The signal is then amplified by Q902 and
fed to another emitter follower Q903.
The audio is coupled to the line driver through C914,
Q904 amplifies the signal. The LINE LEVEL control R936
is connected in the collector circuit of Q904 and allows feed-
ing the audio to the line driver Q907. Q906 serves as an
audio switch controlled by the RUS circuit. As long as the
RUS switch Q909 is turned off (receiver squelched), CR905
is forward biased allowing Q906 to conduct. Conduction of
Q906 grounds the audio path between Q904 and Q907, pre-
venting the audio from being passed to the line. When the re-
ceiver unsquelches, the RUS lead goes high. This turns Q909
on, turning off CR905 and Q906. The audio is now allowed
to pass to the output amplifier Q908 or to the line trans-
former T901. CR902, CR903 and VR901 are provided for
line-surge protection.
When the 19D417261G6 Channel Guard Board is used,
the RX MUTE lead is controlled by the Channel Guard
Board. When no CG tone of the proper frequency is present,
the board holds the RX MUTE lead at ground potential.
When a CG tone of the proper frequency is detected, the
ground on the RX MUTE lead is removed and the RUS lead
will then go high when the receiver squelch opens. Activat-
ing the CG MONITOR switch at the station control unit
causes the Channel Guard Board to remove ground from the
RX MUTE lead, allowing the receiver to operate on noise
squelch.
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