No Or Low Modulation; Figure 4-2. Vco Block Diagram-Uhf Band - Motorola ASTRO Digital Spectra Plus Service Manual

Troubleshooting Procedures: VCO Procedures

4.3.2.4 No or Low Modulation

Under standard test conditions with a 1 kHz tone injected and 4.5 kHz deviation, there should be 700
mV (RMS) ±20% present on P0601-10. If this level is not present, troubleshoot the modulation circuit
on the carrier board and then troubleshoot the audio circuitry. If the proper level is present,
troubleshoot the modulation circuitry on the VCO kit. If no failure exists, replace the VCO.
-SL +SL
P0601
4
OSC
PINSHIFT
CIRCUITRY
P0601
6 11
-8V
AUX1
* MEASURED WITH VCO OUTPUT
TERMINATED INTO 50 OHMS.
6881076C25-D
8.6
3
12
BUFFER
BUFFER
8 dBm Typical*
MODULATION
CIRCUITRY
10
9
AUX2
MODULATION
Figure 4-2. VCO Block Diagram—UHF Band
9.6
2
1ST
X2
DOUBLER
FEEDBACK
BUFFER
SYNTH
SYNTHESIZER
FEEDBACK
_
AUX1, AUX2 HIGH 8V >
AUX1, AUX2 LOW 1V _ <
TX
INJECTION
(16 dBm TYPICAL)
K9.4
5
ACTIVE
BIAS
2ND
BUFFER
1
RX
INJECTION
(12 dBm TYPICAL)
GPW-5861-A
October 28, 2002
4-17