HP 8562E Service Manual page 354

3. Adjust the HP 85623 spectrum analyzer reference level and center frequency to display the
400 Hz modulation frequency eight divisions peak-to-peak.
4. On the HP 85623 spectrum analyzer, press (m), B/FM DEMOI), Mf DF,MOD flly, and
set the sweep time to 5 seconds.
5. Vary the volume and listen for the variation in speaker output level. Clipping is normal at
the highest volume levels.
6. If the audio is not working correctly, monitor the signal at A4U704 pin 3 with an
oscilloscope. The signal should be 20 mV peak-to-peak f25 percent (with t2.5 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 9-39