GE MLSH041 Maintenance Manual page 23

LBI-38438A
ALIGNMENT AND TROUBLESHOOTING PROCEDURES
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.
5.3.5.3 STEP 3: MODULATION ACCEPTANCE BANDWIDTH (OR IF
BANDWIDTH)
If Steps 1 and 2 check out properly, measure the bandwidth as follows:
1. Set the Signal Generator output for twice the microvolt reading obtained in the 12 dB
SINAD measurement.
2. Set the Range control on the Distortion Analyzer in the SET LEVEL position (1000
Hz filter out of the circuit), and adjust the input LEVEL control for a +2 dB reading
on the 30% range.
3. While increasing the deviation of the Signal Generator, switch the RANGE control
from SET LEVEL to distortion range until a 12 dB difference is obtained between
the SET LEVEL and distortion range readings (from +2 dB to –10 dB).
4. The deviation control reading for the 12 dB difference is the Modulation Acceptance
Bandwidth of the receiver. It should be more than ±7 kHz.
SERVICE CHECK
If the Modulation Acceptance Bandwidth test does not indicate the proper width, refer to
the Receiver Troubleshooting Procedure.
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