Motorola ASTRO XTSTM 4000 Detailed Service Manual page 84

5-22
RX RF–Page 2
Remove SH04 and measure
2nd LO at C560 on
VHF: 42.6 MHz
UHF: 71.1 MHz
RX_SSI_CLK (R1123)
RX_SSI_FSYNC (R1125)
RX_SSI_DATA (R1124)
digital signals
bit clock rate (Fbit)
at RX_SSI_CLK
RX_SSI_FSYNC =
20 kHz sync pulse
RX_SSI_FSYNC
May 28, 2008
1
2nd LO, VHF: 42.6 MHz, UHF: 71.1 MHz
about 356 mVpp
PCB side 2
No
Signal
Present?
Yes
LO Freq.
OK?
No
3
Yes
Measure
Observe
0 to 3 Vdc
No
Levels
5
OK?
Yes
Measure
Fbit = No
4
1.2 MHz?
Yes
No
5
OK?
Yes
Troubleshooting Charts: RX RF
2nd LO DC bias
No Check Voltage
Q551-c
= 5.0 Vdc?
Yes
No
Q551-e
= 3.7 Vdc?
Yes
Remove SH11 and
inspect 2nd LO VCO
Visual
No
examination
OK?
Yes
Replace
Q550
RX_SSI_DATA =
24-bit I, 24-bit Q,
8-bit AGC. AGC
varies with RF level
No
RX_SSI_DATA
OK?
Yes
Go to
VOCON RX
AUDIO flowchart
Regulator U1
Replace
Q551
Repair
Defects
5
6871620L01-C