Audio Level Adjustments - Shure LX4 Service Manual

Shure LX4 Diversity Receiver

Audio Level Adjustments

OUTPUTS
HI Z
ANT
BAL
B
MIC LINE
RF SIGNAL GENERATOR
AUDIO ANALYZER
LX4 Receiver
Power: ON
Squelch: Mid
Note: Remove the 33KΩ resistor from test point TPA4 and TPB4.
Note: The amplitude may have to be adjusted so that neither the HI EXT nor the LO EXT LEDs
on the rf signal generator are on. This amplitude should be between 1.4 and 1.5 V rms.
Note: Place a jumper between TPB7 and ground to mute channel B for channel A alignment.
(Place a jumper between TPA7 and ground to mute channel A for channel B alignment.)
Service Procedures
POWER
ANT
A
12.5 – 18.9 VDC
DC BLOCK
Audio Analyzer
Output amplitude: 1.46 V rms
Gain: Max Frequency: 1 kHz
400 Hz High-Pass: ON
30 kHz Low-Pass: ON
Figure 5. Audio Level Adjustments Test Setup
1. Set the rf signal generator frequency to the same as the LX4, its
modulation to FM, its modulation source to EXT, its FM deviation
to 15 kHz, and its amplitude to –60 dBm.
2. Set the audio analyzer's audio frequency to 1 kHz and its
amplitude to 1.46 V rms.
3. Connect the output of the audio analyzer to the input of the
rf signal generator.
4. Place a probe on TPA5, U1, pin 1 (TPB5) and adjust
L110 (L210) for maximum ac voltage.
5. With the probe still on TPA5 (TPB5), adjust R59 (R58) for
0.775 V ± 50 mV rms (1 kHz tone).
Repeat this test for channel B.
18
TPA5
TPB5
R59
L110
R58
NOTE: DC VOLTAGES ARE PRESENT AT MOST
RF TEST POINTS. USE A DC BLOCK ON THE
RF SIGNAL GENERATOR TO PROTECT
TEST EQUIPMENT.
Rf Signal Generator
Modulation: FM
Filters: Mod source: EXT
L210
Frequency: carrier
Amplitude: –60 dBm
Deviation: 15 kHz
25D1008 (BK)