HP 8924E, Assembly

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Chapter 14, Diagnostics Descriptions
Description Of Audio Diagnostics (AFDIAGS3)
N:\mkt\MANUALS\HP8924C\ALR\diagnos.fb
Preliminary Audio Paths
This test checks the ability of the A4 Modulation Distribution assembly to route
an audio signal from Audio Frequency Generators, to the monitor select switch,
and to the AM and FM modulators. It checks that the audio leaves the A4
assembly, but does not check whether it actually gets to the AM and FM
modulators. The test that follows this one (Modulation Distribution Internal
Paths) does the fine-resolution testing of the circuits.
This is a test of the integrity of the Modulation Distribution assembly. It verifies
the functioning of the signal-routing switches. The nine paths in this test are
shown as heavy lines in
figure 51
through
figure 56
.
NOTE: In these figures, three circuits on the Modulation Distribution assembly (AFG1 Amplifier,
AFG1 Level Amplifier, and AFG1 Attenuator 1) are combined into one circuit block labeled
AFG1 Circuits. This also applies to AFG2. Refer to
figure 58 which explicitly shows these
circuits.
Measurement limits are
±
10% of nominal when a signal is expected at the output
(Paths 1, 3, 5, 6, 7, and 9). The limits are
±
20 mV when the signal should be
absent (Paths 2, 4, and 8). It is also as important to check paths which are intended
to block signals (that is, that expect no output) as it is to check paths that should
pass signals.
Paths which block signals are open switches (in Paths 2 and 4) or blocking
capacitors with DC applied (in Path 8).
All paths are stimulated with DC except Path 9. Path 9 checks the DC blocking
capacitor that couples signal to the front-panel AUDIO OUT port. Path 9 is the
only path that uses a Peak Detector.
All measurements in this test are made with fixed level and gain parameters. Only
signal-routing switch settings and the waveform of Audio Frequency Generator 2
are changed. The fixed settings are as follows:
• Level of Audio Frequency Generators 1 and 2 (AFG1 and AFG2) set to 1 V.
• Frequency of Audio Frequency Generator 2 set to 1 kHz in AC.
• Gain of AFG 1 and 2 Level Amplifiers set to 0.784 (DAC set to 200 out of a maximum
of 255).
• Attenuation of AFG1 and AFG2 Attenuator 1 set to 0 dB.
• Attenuation of AFG1 and AFG2 Attenuator 2 set to 0 dB.