Figure 4-2. Frequency Generation Unit Block Diagram (Vhf); Table 4-6. Lv Frac-N U3751 Pin Descriptions (Vhf) - Motorola ASTRO Digital XTL 5000 Detailed Service Manual

Troubleshooting Procedures: VHF (136–174 MHz) Band Main Board Troubleshooting
5.0V
16.8MHz OSC
3.0V
Regulator
U3750
CLOCK
SYN_SEL
From
Controller
DATA
MOD_IN
PHASE
DETECTOR IAS
Q3755 RX and
Q3750 TX
9.3V
8.2V
Super Filter
Q3756

Figure 4-2. Frequency Generation Unit Block Diagram (VHF)

Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
6881096C74-B
3.0V
3.0V
16.8MHz Reference
U3752
VOLTAGE
MULTIPLIER
3.0V
D3758 and
3.0V
VMULT3
VMULT4
AUX1
AUX2
U6751
IOUT
IADAPT
Mod Out
C3809
ias 1
ias 2
AUX3
AUX4
SFIN
SF ASE
PREIN
Lock
SFOUT
8.2V

Table 4-6. LV Frac-N U3751 Pin Descriptions (VHF)

Pin Name Description
AUX2 Auxiliary logic output, high selects Low TX VCO
AUX3 Auxiliary logic output, high selects Low RX VCO
AUX4 Auxiliary logic output, high selects High RX VCO
LOCK Lock detect—logic high indicates in-lock condition
PD_VDD 3.0-V supply (phase detector)
GROUND Ground (digital)
DATA SPI data I/O
CLK SPI clock
CEX SPI enable line—active low
MODIN Modulation input from controller
VMULT4 Multiplier clock output
VMULT3 Multiplier clock output
to Controller and
Receiver ack End
8.2V
D3757
8.2V SW
8.2V SW
Tx VCOs
Q3753
Q3765
Q3763
Q3754
LOOP
FILTER
Q3751
Q3766
Q3764
Q3752
Rx VCOs
Prescaler Input
Lock Detect
to Controller
Keyed
9.1V
TX
TX
uffers
Injection
8.2V SW
8.2V SW
9.3V
RX
RX
uffers
Injection
8.2V
RF
Q3757
Feedback
MAEPF-27804-O_VHF
May 25, 2005
4-9