Service manual

Shure LX2 Hand-Held Transmitter
Preliminary Tests11
25D1006 (CG)
Check the Transmitter
AUDIO ANALYZER
12.5 – 18.9 VDC
ANTANT
OUTPUTS
HI Z
BAL
MIC LINE
POWER
AB
LX4 RECEIVER
TRANSMITTER SHOWN WITH
BATTERY CUP REMOVED, AND
AUDIO TEST HEAD ATTACHED.
Audio Test Head
PT1840
LX2 Transmitter LX4 Receiver Audio Analyzer
Power switch: PWR Power switch: ON Frequency: 1 kHz
Gain: Min Gain: Max Amplitude: .775 V
Mute switch: MUTE Squelch: Mid Filters:
Low-Pass (30 kHz): ON
High-Pass (400 Hz): ON
Figure 5. Transmitter Functional Test
1. Disconnect the rf signal generator from the receiver and turn the
rf power off. Monitor the receiver’s unbalanced audio output with
a 3.3 kΩ load and the audio analyzer. Turn the receiver’s volume
control to its maximum setting.
2. Use an audio test head to input audio into the hand-held trans-
mitter.
3. Turn the LX2 ON.
4. Inject a 0.775 V, 1 kHz signal from the audio analyzer into
the audio test head. Transmitter gain should be set to minimum.
Verify the following:
S the amplitude from the receiver’s unbalanced output equals
400 mVrms ("90 mV)
S total harmonic distortion (THD) is < 0.75%
5. Change the frequency of the audio generator to 100 Hz and
disengage the 400 Hz high-pass filter from the audio analyzer.
Verify that the audio level is –.5 dB ("0.5 dB) relative to the level
measured above.
6. Change the frequency of the audio generator to 10 kHz and
reengage the 400 Hz high-pass filter. Verify that the audio level,
relative to that measured above, is 0 dB, "2 dB.