Motorola Astro Digital Mobile Radio Xtl5000 Detailled 6881096c74 B Manual

6881096C74-BMay 25, 2005
Troubleshooting Procedures: UHF Range 2 (450–520 MHz) Band Main Board Troubleshooting 4-17
4.8 UHF Range 2 (450–520 MHz) Band Main Board Troubleshooting
This information will help you troubleshoot the RF section of the UHF Range 2 (450–520 MHz) band 
XTL 5000 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,...

May 25, 20056881096C74-B
4-18Troubleshooting Procedures: UHF Range 2 (450–520 MHz) Band Main Board Troubleshooting
NOTE:The UHF band radios use high-side injection with an IF frequency of 109.65 MHz; therefore, 
the receive VCO frequencies are 109.65 MHz higher than the selected radio channel 
frequencies.
NOTE:If a failure is indicated in any of the VCOs, whose operation is defined in the table above, then 
the respective circuit should be checked to ensure proper bias is being applied to the...

6881096C74-BMay 25, 2005
Troubleshooting Procedures: UHF Range 2 (450–520 MHz) Band Main Board Troubleshooting 4-19
4.8.2 FGU Troubleshooting Aids
The following illustrations are additional service aids for troubleshooting the frequency generation 
unit.
•Figure 4-7 is a block diagram of the DC distribution for the frequency generation unit.
•Figure 4-8 on page 4-20 is a block diagram of the frequency generation unit.
•Table 4-12 on page 4-20 describes the function of pins on the LV Frac-N IC U5752....

May 25, 20056881096C74-B
4-20Troubleshooting Procedures: UHF Range 2 (450–520 MHz) Band Main Board Troubleshooting
Figure 4-8.  Frequency Generation Unit Block Diagram (UHF Range 2)
Table 4-12.  LV Frac-N U6751 Pin Descriptions (UHF Range 2)
Pin No.Pin NameDescription
1AUX2 Auxiliary logic output
2AUX3 Auxiliary logic output
3AUX4 Auxiliary logic output
4LOCK Lock detect—logic high indicates in-lock condition
5PD_VDD 3.0-V supply (phase detector)
6GROUND Ground (digital)
7DATA SPI data I/O
8CLK SPI...

6881096C74-BMay 25, 2005
Troubleshooting Procedures: UHF Range 2 (450–520 MHz) Band Main Board Troubleshooting 4-21
15
VMULT1 Not used
16INDMULT Not used
17— No connection
18REFSEL Not used
19FREFOUT Not used
20AVDD 3.0-V supply (analog)
21VBPASS Not used
22GND Ground (analog)
23XTAL1 16.8 MHz reference oscillator input
24XTAL2 Not used
25WARP Reference oscillator warp output
26SFCAP Superfilter bypass node
27SFBASE Superfilter control node for Q5752
28SFOUT Superfilter output
29— No connection
30SFIN...

May 25, 20056881096C74-B
4-22Troubleshooting Procedures: 700–800 MHz Main Board Troubleshooting
Figure 4-9.  Waveform Representation During Programming of the LV Frac-N IC (U5752)
NOTE:The above waveforms are representations only.
4.8.3 Out-of-Lock Condition
The probable cause of an out-of-lock condition is a failure in the synthesizer circuit. If the voltages on 
the AUX lines do not conform to Table 4-11 on page 4-18, troubleshoot the synthesizer. If the AUX 
pins are correct, but the supply switch...

6881096C74-BMay 25, 2005
Troubleshooting Procedures: 700–800 MHz Main Board Troubleshooting 4-23
4.9.1 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...

May 25, 20056881096C74-B
4-24Troubleshooting Procedures: 700–800 MHz Main Board Troubleshooting
3. Continue troubleshooting by using the Fail 001 troubleshooting chart in Chapter 5.
4.9.2 FGU Troubleshooting Aids
The following illustrations are additional service aids for troubleshooting the frequency generation 
unit.
•Figure 4-10 on page 4-25 is a block diagram of the DC distribution for the frequency generation 
unit.
•Figure 4-11 on page 4-26 is a block diagram of the frequency generation unit....

6881096C74-BMay 25, 2005
Troubleshooting Procedures: 700–800 MHz Main Board Troubleshooting 4-25
Figure 4-10.  Frequency Generation Unit DC Power Supply Distribution (700–800 MHz)
MAEPF-27803-O
13.8 VDC
from Battery or
Power Supply
Q0503
Switched A+
Switched A+
(SW_A+)
9.3V
Regulated
5.0V
Regulated8.2V
RegulatedK9.1
3.0V
Regulated U0950
9.3V Regulator
U0505
5.0V Regulator
U6750
3.0V Regulator
Y6750 16.8
MHz Reference
Oscillator and
U6752 BufferQ6759
8.2V Superfilter
U6754 TX VCOs
and
U6755 RX VCOs
U6751...

May 25, 20056881096C74-B
4-26Troubleshooting Procedures: 700–800 MHz Main Board Troubleshooting
Figure 4-11.  Frequency Generation Unit Block Diagram (700–800 MHz)
Table 4-15.  LV Frac-N U6751 Pin Descriptions (700–800 MHz)
Pin No.Pin NameDescription
1AUX2 Auxiliary logic output, high selects U6754 OSC2
2AUX3 Auxiliary logic output, high selects U6755 OSC1
3AUX4 Auxiliary logic output, high selects U6755 OSC2
4LOCK Lock detect—logic high indicates in-lock condition
5PD_VDD 3.0-V supply (phase detector)...