HP 8924C Assembly page 562

Chapter 14, Diagnostics Descriptions
Description Of Audio Diagnostics (AFDIAGS3)
Modulation Distribution External Paths
562
This test checks the ability of the A34 Modulation Distribution assembly to route
an external modulation signal to the monitor output of the A34 assembly. It also
checks the ability of the A34 assembly to adjust the level of an external
modulation signal. The paths which relate to internal inputs are checked in the
previous test.
This test checks the Modulation Distribution assembly's path from the rear-panel
MODULATION INPUT to the Monitor Select output. Before doing this, the path
from Audio Frequency Generator 1 to the Monitor Select is checked to assure that
the audio source can be used as an external test signal via the front-panel AUDIO
OUT connector. The paths are illustrated in
Audio Generator 1 is the signal source for all measurements (internal or external).
The signal is DC except where AC coupling is checked (Path 7). Measurement
±
limits are 10% of nominal when a signal is expected at the output, and
when the signal is absent (this occurs when the Modulation Select Source Switch
is set to open and when DC is applied to blocking capacitor of Mod In AC/DC
coupling). However, the limit on DAC-gain controlled amplifiers is
±
nominal 40 mV.
In Path 1 the integrity of the internal signal at the AUDIO OUT connector is
tested. In Path 2 the signal is routed externally to the MODULATION INPUT
connector where it is measured through the shortest path (which goes from the
output of the Modulation Input Buffer Amplifier to the Monitor Multiplexer
Select Source switch).
The strategy for checking the DAC-controlled external level amplifier is similar to
the strategy for the previous test. This amplifier has two variable-gain stages: (1) a
stage which sets the level based on user input and (2) a fine-adjustment stage
which is factory- or user-calibrated to correct for variations in overall path gain.
Stage 1 is tested with a "walking 1"; stage 2 is tested at one point (DAC set to
255).
The external attenuator is checked for gains of 1 and 0.1.
The failure codes for the Modulation Distribution assembly's external paths are as
follows:
through
figure 59 figure 61
N:\mkt\MANUALS\HP8924C\ALR\diagnos.fb
.
±
40 mV
±
10% of