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Troubleshooting Procedures: UHF Range 1 (380–470 MHz) Band Main Board Troubleshooting
Figure 4-3. Waveform Representation During Programming of the LV Frac-N IC (U3751)
NOTE: The above waveforms are representations only.
4.6.5
No or Low Output Power (TX or RX Injection)
In addition to the schematic and theory of operation, refer to the transmitter injection troubleshooting
flowchart and the receiver injection trouble shooting flowchart in Chapter 5. The charts will guide you
through a sequence of tests and checks designed to isolate problems in the Transmitter or receiver
injection strings.
4.6.6
No or Low Modulation
In addition to the schematic and theory of operation, refer to the transmitter no TX Audio
troubleshooting flowchart in Chapter 5. The chart will guide you through a sequence of tests and
checks designed to isolate problems in the Transmitter Audio section of the FGU.
4.6.7
Troubleshooting the Back-End
Refer to
"5.6.4 RX Back-End—Poor SINAD or No Audio (136–174 MHz)—Part 1 of 3" on page
4.7
UHF Range 1 (380–470 MHz) Band Main Board Troubleshooting
This information will help you troubleshoot the RF section of the UHF Range 1 (380–470 MHz) band
XTL 1500 radio. Use this information, along with the theory of operation and troubleshooting charts,
to diagnose and isolate the cause of failures.
Prior to troubleshooting, it is important to review the theory of operation, including specific
precautions and troubleshooting methods. Because much of the radio's circuitry operates at high
frequencies, measurements must be taken very carefully. Notes and cautions are added to the text
to alert you to this need in areas of greatest sensitivity. However, the need for extreme care does
exist in all measurements and tests.
4.7.1
Display Flashes "FAIL 001"
This display indicates a synthesizer "out-of-lock" condition. The following information will help to
trouble shoot the frequency generation unit to the component level. Perform the following checks to
determine the mode of the Fail 001:
1. Determine if the "out-of-lock" condition occurs in either receive mode, transmit mode, or both.
Also, check other frequencies programmed in the unit if available.
2. To determine if the "out-of-lock" is frequency or VCO dependant, place the unit into RF TEST
Mode, as described in the ASTRO Digital XTL 1500 VHF/UHF Range 1/UHF Range 2/700–
800 MHz Mobile Radio Basic Service Manual (6815853H01) and step through each test
channel.
mode channel. In addition,
of operation for each VCO.
6815854H01-A
Pin 9 (Chip Select)
Pin 7 (Data)
Pin 8 (Clock)
Table 4-7 on page 4-12
indicates the frequency and Aux logic level for each test
Table 4-8 on page 4-12
MAEPF-27805-O
provides information about the frequency
4-11
5-15.
June 15, 2005
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Table of Contents
Troubleshooting
