No Or Low Modulation; Figure 4-2. Vco Block Diagram - Uhf Band - Motorola ASTRO Digital Spectra 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
9
AUX2
-8V
AUX1
* MEASURED WITH VCO OUTPUT
TERMINATED INTO 50 OHMS.
68P81076C25-C
8.6
3
12
1ST
BUFFER
BUFFER
8 dBm Typical*
MODULATION
CIRCUITRY
10
MODULATION
AUX1, AUX2 HIGH 8V
AUX1, AUX2 LOW 1V

Figure 4-2. VCO Block Diagram - UHF Band

9.6
K9.4
2
ACTIVE
BIAS
2ND
X2
BUFFER
DOUBLER
FEEDBACK
BUFFER
SYNTH
1
SYNTHESIZER
FEEDBACK
_
>
_ <
4-17
TX
INJECTION
(16 dBm TYPICAL)
5
RX
INJECTION
(12 dBm TYPICAL)
GPW-5861-A
July 1, 2002