Motorola Astro Digital Mobile Radio Xtl5000 Detailled 6881096c74 B Manual

6881096C74-BMay 25, 2005
Troubleshooting Procedures: VHF (136–174 MHz) Band Main Board Troubleshooting 4-7
4.6.3 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 1*, AUX 2*, AUX3*, and AUX4* lines do not conform to required output frequency in
Table 4-5, troubleshoot the synthesizer.
If the AUX 1* to AUX 4* voltages are correct but the synthesizer feedback level is not within the 
range indicated, troubleshoot the...

May 25, 20056881096C74-B
4-8Troubleshooting Procedures: VHF (136–174 MHz) Band Main Board Troubleshooting
Figure 4-1.  Frequency Generator Unit DC Power Supply Distribution (VHF)
MAEPF-27803-O_VHF
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
U3750
3.0V Regulator
Y3750 16.8
MHz Reference
Oscillator and
U3752 BufferQ3756
8.2V Superfilter
Q3753,Q3754
TX VCOs
and...

6881096C74-BMay 25, 2005
Troubleshooting Procedures: VHF (136–174 MHz) Band Main Board Troubleshooting 4-9
Figure 4-2.  Frequency Generation Unit Block Diagram (VHF)
Table 4-6.  LV Frac-N U3751 Pin Descriptions (VHF)
Pin No.Pin NameDescription
1AUX2 Auxiliary logic output, high selects Low TX VCO
2AUX3 Auxiliary logic output, high selects Low RX VCO
3AUX4 Auxiliary logic output, high selects High RX VCO
4LOCK Lock detect—logic high indicates in-lock condition
5PD_VDD 3.0-V supply (phase detector)
6GROUND...

May 25, 20056881096C74-B
4-10Troubleshooting Procedures: VHF (136–174 MHz) Band Main Board Troubleshooting
13
VRO 3.0-V supply for reference oscillator warp circuitry
14VMULT2 Not used
15VMULT1 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...

6881096C74-BMay 25, 2005
Troubleshooting Procedures: UHF Range 1 (380–470 MHz) Band Main Board Troubleshooting 4-11
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...

May 25, 20056881096C74-B
4-12Troubleshooting Procedures: UHF Range 1 (380–470 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 1 (380–470 MHz) Band Main Board Troubleshooting 4-13
4.7.2 FGU Troubleshooting Aids
The following illustrations are additional service aids for troubleshooting the frequency generation 
unit.
•Figure 4-4 is a block diagram of the DC distribution for the frequency generation unit.
•Figure 4-5 on page 4-14 is a block diagram of the frequency generation unit.
•Table 4-9 on page 4-14 describes the function of pins on the LV Frac-N IC U5752....

May 25, 20056881096C74-B
4-14Troubleshooting Procedures: UHF Range 1 (380–470 MHz) Band Main Board Troubleshooting
Figure 4-5.  Frequency Generation Unit Block Diagram (UHF Range 1)
Table 4-9.  LV Frac-N U6751 Pin Descriptions (UHF Range 1)
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 clock...

6881096C74-BMay 25, 2005
Troubleshooting Procedures: UHF Range 1 (380–470 MHz) Band Main Board Troubleshooting 4-15
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
4-16Troubleshooting Procedures: UHF Range 1 (380–470 MHz) Band Main Board Troubleshooting
Figure 4-6.  Waveform Representation During Programming of the LV Frac-N IC (U5752)
NOTE:The above waveforms are representations only.
4.7.3 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 4-8 on page 4-12, troubleshoot the synthesizer. If the AUX 
pins are correct, but the...