Receiver Test Procedures; Test Procedure - GE MLSH041 Maintenance Manual

ALIGNMENT AND TROUBLESHOOTING PROCEDURES

5.3.4 Receiver Test Procedures

5.3.5 Test Procedure

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5. Check that the squelch opens at an input signal level corresponding to 8 dB SINAD
(±1 dB).
6. Remove ground from J701-7 or re-enable Channel Guard.
These Test Procedures are designed to help you service a receiver that is operating, but
not properly. The problems encountered could be low power, poor sensitivity, distortion,
and low gain. By following the sequence of test steps starting with Step 1, the defect can
be quickly localized. Once the defective stage is pin-pointed, refer to the "Service
Check" listed to correct the problem. Additional corrective measures are included in the
Troubleshooting Procedures. Before starting with the Receiver Test Procedures, be sure
the receiver is tuned and aligned to the proper operating frequency and the transmitter is
operating properly.
5.3.4.1 TEST EQUIPMENT REQUIRED
1. Distortion Analyzer
2. Signal Generator
3. 6 dB Attenuation Pad, and 4.0 ohm, 6 Watt Resistor
5.3.5.1 STEP 1: AUDIO OUTPUT AND DISTORTION
Measure Audio Power Output as follows:
1. Apply a 1000 microvolt, on-frequency test signal modulated by 1000 Hz with 3.0
kHz deviation to antenna jack J1.
2. With 4 Watt Speaker: Disconnect speaker plug if present. Connect a 4.0 ohm, 6 watt
load resistor across the external speaker loads
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).
5.3.5.2 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.
LBI-38438A