TM 11 -5820-890-20-1
CHAPTER 3
VEHICULAR RADIO CONFIGURATIONS
Subject
Para
Page
Operational Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1
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Troubleshooting Flowcharts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2
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3.1.
OPERATIONAL CHECK.
The following Operational Check for Vehicular Radio Configurations, identical in both TM 20-1 and TM 20-3
(Unit Maintenance Handbook) is used initially to identify what is wrong with a vehicular radio system and
determine what corrective action needs to be taken at Unit Maintenance. After corrective action has been taken,
this Operational Check is used a second time to verify that the system is fully operational.
The Unit Maintainer, using this Operational Check, determines if FIT-A, FIT-B, or both are to be checked, and
whether the problem radio is short range or long range. The Unit Maintainer also determines which other items
of ancillary equipment such as intercommunications systems, loudspeakers, and control-monitors, are involved
and skips those Operational Check actions that do not apply. Wiring diagrams of Short Range RT-A and
RT-B, plus Long Range RT-A and RT-B, are provided at the front of the Troubleshooting section (Paragraph
3.2) for ease of reference.
In checking vehicular radio systems that contain a Vehicular Amplifier-Adapter (VAA), the Unit Maintainer must
determine which of the five current models is present: AM-7239 SERIES. The principal difference among these
models is in the method of selecting LOCAL and REMOTE operation. The AM-7239 uses a shorting bar which is
changed by removing a cover panel on the side of the VAA. The AM-7239A uses a shorting jumper, also
located behind a cover panel. The AM-72396, AM-7239C and AM-7239D uses a LOCAL/REMOTE switch which
is visible to the left of the RT-B J7 system connector. AM-7239E uses a LOCAL/REMOTE switch which is visible
to the right of CB1. Chapter 1 provides both explanations and graphics of these differences (refer to paragraph
1.9.e). Whenever necessary, Operational Checks and Troubleshooting Flowcharts/Guides provide separate
actions by VAA model.
Corrective actions are either specifically stated (for example, Replace RT), or the Unit Maintainer is advised of
the Troubleshooting Flowchart (TS CHART) to use. Use of the Operational Check after corrective action has
been taken helps to ensure that the vehicular radio is in fact operational, and greatly reduces the possibility of
false pulls at Unit Maintenance.
RT-1523E HUB Insert relpacement
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