800 Mhz Band; Vco Hybrid Assembly; Out-Of-Lock Condition; Figure 4-3. Vco Block Diagram-800 Mhz Band - Motorola ASTRO Digital Spectra Plus Service Manual

4-18
4.3.3

800 MHz Band

Use these instructions along with the Theory of Operation, the block diagram, and the schematic to
help isolate failures, first, to the individual circuits, and finally to the failing piece part.

4.3.3.1 VCO Hybrid Assembly

The VCO hybrid substrate is glued to the carrier board. The hybrid is not a field-repairable assembly.
If a failure is indicated in this assembly, replace the entire carrier board.

4.3.3.2 Out-of-Lock Condition

The probable cause of an out-of-lock condition is a failure in the synthesizer circuit. (See
Section 4.1.4.2 on page
table in Figure 4-3, troubleshoot the synthesizer.
If the AUX 1* and AUX 2* voltages are correct but the synthesizer feedback level is not within the
range indicated, troubleshoot the first buffer on the VCO carrier board. If no problem is found with the
first buffer and the level out of the VCO is below that indicated on the block diagram, check J straps
MP9656-MP9668. If no problem is found with these, replace the entire carrier board.
If the AUX 1* and AUX 2* voltages are correct and the synthesizer feedback level is correct but an
out-of-lock condition persists, troubleshoot the synthesizer.
OSC
VCO HYBRID
CARRIER BOARD
October 28, 2002
4-7.) If the voltages on the AUX 1* and AUX 2* lines do not conform to the
+1.0 dBm 1ST
DOUBLER
Min
BUFFER
PAD
SYNTH FEEDBACK
RX = 370.675 - 379.675
TX = 403.000 - 412.000
TA = 425.500 - 434.500
-
FREQUENCY
AUX1
RANGE
RX HI
TX HI
TA LOW
Figure 4-3. VCO Block Diagram—800 MHz Band
Troubleshooting Procedures: VCO Procedures
TX/RX
SWITCH
2ND
BUFFER
PAD
6.0 dBm + 7 dBm
-
AUX2 OUTPUT FREQUENCY
HI 741.35 - 759.35
LOW 806.00 - 824.00
LOW 851.00 - 869.00
TX TX = 806 - 824
INJ TA = 851 - 869
741.35 - 759.35
RX INJ
GPW-6395-O
6881076C25-D