3.Adjust the spectrum analyzer reference level and center frequency to display the 400 Hz modulation frequency eight divisions peak-to-peak.

4.On the spectrum analyzer press (mCTRL), AM/FM DEMOD , AM DEMOD ON, and set the sweep time to 5 seconds.

5.Vary the volume and listen for the variation in speaker output level. Clipping is normal on the highest settings.

6.If the audio is not working correctly monitor the signal at A4U704 pin 3 with an oscilloscope. The signal should be 190 mV rms *25% (with +5 V of dc bias). If the signal measures outside these limits, the fault is prior to the audio amplifier (block T)

7.If the signal is correct, troubleshoot the audio amplifier and speaker.

IF Section 8-41