Vocon Rx Audio - Motorola ASTRO XTS 5000 Detailed Service Manual

5-24
RX RF—Page 2
Measure 2nd LO at
TP501 (UHF & 700-800)
or TP18 (VHF)
on PCB side 2
Present?
LO Freq.
VHF: 42.6 MHz
UHF: 71.1 MHz
700-800:
107.4 MHz
Measure
RXCK, P1-5
RXFS, P1-6
RXDO, P1-12
Observe
0 to 3 Vdc
digital signals
Measure
bit clock rate
(Fbit) at RXCK
1.2 MHz?
RXFS = 20 kHz
sync pulse
October 14, 2003
1
2nd LO, 700-800: 107.4 MHz, VHF: 42.6 MHz, about 356 mVpp
No
Signal
Yes
OK?
No
3
Yes
Levels No
5
OK?
Yes
Fbit = No
4
Yes
No
RXFS
5
OK?
Yes
Troubleshooting Charts: RX RF
2nd LO DC bias
No
Q501-c
= 5.0 Vdc?
Yes
No
Q501-e
= 3.7 Vdc?
Yes
Remove SH501
(UHF & 700-800)
or SH502 (VHF), inspect
2nd LO VCO
Visual
No
examination
OK?
Yes
Replace
Q502
RXDO = 24-bit I,
24-bit Q, 8-bit
AGC. AGC varies
with RF level
RXDO
OK?
Yes
Go to
VOCON RX
AUDIO flowchart
Check Voltage
Regulator U1
Replace
Q501
Repair
Defects
No
5
MAEPF-27471-B
6881094C31-C