HP 8924E, Assembly

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Chapter 14, Diagnostics Descriptions
Description Of Audio Diagnostics (AFDIAGS3)
N:\mkt\MANUALS\HP8924C\ALR\diagnos.fb
Modulation Distribution Internal Paths
The Modulation Distribution assembly paths that relate to inputs from the two
Audio Frequency Generators are tested. The paths are the same as in the
Preliminary Audio Paths test; however, the circuits are tested more thoroughly by
varying settable parameters (gain and attenuation). The paths are illustrated in
figure 57, "Modulation Distribution Internal Paths 1 to 4," on page 560
and
figure 58, "Mod Distribution Internal Paths 5-8 (Paths 9-11 check Internal Pre Mod
Filters)," on page 561
.
The audio sources are set to AC. The measurements at the DVM are always DC
since the signal is routed to the Peak Detector in Audio Analyzer 2 (this is not
shown in
figure 57
and
figure 58
). Measurement limits are
±
10% of nominal
±
10
mV offset when a signal is expected at the output, and
±
10 mV when the signal is
absent (when Attenuator 2 is set to open).
In this test, a “walking 1” (that is, 0, 1, 2, 4,…, 128, 255) is programmed into the
gain-control DAC of the Level Amplifiers. In normal use the highest DAC setting
is 200. The system gain was discussed in the Preliminary Audio Paths test.
Attenuator 1s are set to attenuation’s of 1 and 0.1. Attenuator 2s are set to
attenuation’s of 1, 0.01, and open. Do not confuse Attenuators 1 and 2. There are
two Attenuator 1s, AFG1 Attenuator 1 and AFG2 Attenuator 1; there are two
Attenuator 2s, AFG1 Attenuator 2 and AFG2 Attenuator 2.
There are three low-pass filters (150 Hz, 250 Hz, and 20 kHz) in the path for
AFG2. The three filters are tested in measurement paths 9, 10, and 11 (not shown
in
figure 58
).