Ericsson MDX SERIES, Service Manual, Page: 8 / 14

Low Speed Data and Channel Guard Check
1. Turn on the 11 Hz signal (low speed data). Verify TX
modulation is 0.75 kHz
±
0.25 kHz. Adjust R250 for mini-
mum deviation.
2. Turn on 150 cps data and verify transmit modulation is 750
±
0.25 kHz.
RECEIVER ALIGNMENT
Frequency Set
1. Verify that the transmitter is on frequency as described in
the transmitter alignment procedure.
2. Inject a strong on-channel signal (-50 dBm) at the antenna
input J101.
3. Monitor J501 with a frequency counter and adjust L508
for a reading of 455 kHz
±
100 Hz.
IF Tuning
1. Monitor J501 pin 1 with an AC voltmeter (pin 2 is ground).
Inject an on-channel signal at the antenna jack modulated
with a 1 kHz tone at 3 kHz deviation.
2. Adjust L504, L506, and L507 for a peak on the voltmeter.
Adjust the level of the generator to keep the signal at J501
out of limiting (approximately -65 dBm)
3. Repeak the coils.
Quadrature Detector Adjustment
1. Inject a strong (-60 dBm) on-channel signal at the antenna
jack modulated with a 1 kHz tone at 3.0 kHz deviation.
2. Monitor the VOL/SQ HI output at J705-3 with an AC
voltmeter and adjust L509 for a peak indication on the
meter.
Receiver Audio Level
1. Inject a strong on-channel signal at the antenna jack modu-
lated with a 1 kHz tone at 3.0 kHz deviation.
2. Monitor VOL/SQ HI at J702-4 on the audio board with an
AC voltmeter. Adjust R513 on the RF board for a reading
of 1.5
±
0.1 Vrms.
Squelch Adjust
1. Select any channel. Apply a signal modulated with a 1 kHz
tone at 3.0 kHz deviation to the antenna jack.
2. Press and hold the SCAN button on the radio and use the
Volume Up/Down to open/close the squelch.
3. While monitoring SPKR HI J725-3, adjust the signal gen-
erator for 8 dB SINAD.
4. While holding the SCAN button press the Volume Down
button until you hear a pop (squelch fully closed). Now
press the Volume Up button until the squelch just opens.
5. Check adjustment by turning signal generator RF level
down slowly until squelch closes. Slowly bring RF level
back up. Squelch should open at 8 dB SINAD.
POWER DISTRIBUTION
Refer to the Power Distribution Block Diagram for an
understanding of the distribution of A+, SW A+, and the
regulated voltages throughout the radio.
A+
A+ (+13.8 volts nominal) enters the radio on the power
cable and is connected to the system board. A+ feeds MOSFET
switch Q903 which provides SW A+ power to the audio
amplifier board through A5 J902 and A6 J901. A+ is also
applied to the display board through A6 J707 and P707 on the
display board.
A+ leaves the system board on J903 and feeds the PA board
and RF transistor Q151 through feedthru capacitor assembly
Z903. D905 on the system board provides reverse polarity
protection for the radio. D904 provides overvoltage positive
spike protection on the system board A+ lead. A+ leaves the
board on J151 and supplies power to PA module U101 and
Q101 on the RF board. Q101 supplies the power control
voltage to the PA module.
ALIGNMENT PROCEDURE
To align the radio, test mode operation should be used as described in the Test Preparation section. Refer to the assembly diagrams
for board location and to Figure 3 for adjustment and test point locations.
Figure 3 - Location Of Controls And Adjustments, RF Board
LBI-38851 LBI-38851
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