Comnet MLS II MLSH041, Руководство по обслуживанию

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LBI-38425A ALIGNMENT AND TROUBLESHOOTING PROCEDURES
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3. Adjust the VOLUME control for rated power output of 4 watts (4.0 Vrms across the
4 ohm load) using the Distortion Analyzer as a voltmeter.
4. Make distortion measurements according to manufacturer’s instructions. Reading
should be less than 5%. If the receiver sensitivity is to be measured, leave all
controls and equipment as they are.
Service Check
If the distortion is more than 5%, or maximum audio output is less than 4 watts, make the
following checks: Battery and regulator voltage, low voltage will cause distortion.
Audio Gain (refer to Receiver Troubleshooting Procedure).
FM Detector Alignment (refer to Receiver Alignment).
STEP 2: Usable Sensitivity (12 dB SINAD)
If Step 1 checks out properly, measure the receiver sensitivity as follows:
1. Apply a 1000 microvolt, on-frequency signal modulated by 1000 Hz with 3 kHz
deviation to J1.
2. Place the RANGE switch on the Distortion Analyzer in the 200 to 2000 Hz distortion
range position (1000 Hz filter in the circuit). Tune the filter for minimum reading or
null on the lowest possible scale (100%, 30%, etc.).
3. Place the RANGE switch to SET LEVEL position (filter out of the circuit) and
adjust the input LEVEL control for a +2 dB reading on a mid range (30%).
4. Set signal generator output to 0.3 V. Switch the RANGE control from SET LEVEL
to the distortion range. Readjust Distortion Analyzer SET LEVEL as required until
a 12 dB difference (+2 dB to –10 dB) is obtained between the SET LEVEL and
distortion range positions (filter out and filter in).
5. The 12 dB difference (Signal plus Noise and Distortion to noise plus distortion ratio)
is the “usable” sensitivity level. The sensitivity should be less than rated 12 dB
SINAD specifications with an audio input of at least 2 watts (2.83 Vrms across the 4
ohm receiver load using the meter).
6. Leave all controls as they are and all equipment connected if the Modulation
Acceptance Bandwidth test is to be performed.
Service Check
If the sensitivity level is more than rated 12 dB SINAD, check the alignment of the IF
stage as directed in the Alignment Procedure.
STEP 3: Modulation Acceptance (Bandwidth or IF Bandwidth)
If Steps 1 and 2 check out properly, measure the bandwidth as follows: