Motorola Astro Digital Mobile Radio Xtl5000 Detailled 6881096c74 B Manual

							6881096C74-BMay 25, 2005
Troubleshooting Charts: Flowcharts5-51
5.6.37 RX Back-End—Poor SINAD or No Audio (700–800 MHz)—Part 2 of 3
Figure 5-39.  RX Back-End—Poor SINAD or No Audio (700–800 MHz)—Part 2 of 3
No
33 1
TP6001
= 5.0V?
No
Ye sYe s
TP6001
= 0.0V? No
Ye s Freq
VCO 75.6
MHz? Measure
control voltage
at TP6001
Inspect 2nd LO VCO
for missing parts or
solder defect
Ye sNo Visual
inspection
OK?Repair defects
and/or replace
suspect parts
Replace
varacter diode
D6051
MAEPF-27807-O
TP6001
VOLTS DCNOMINAL
FREQ (MHz)
0.0
1.6
4.0
5.068.0
71.1
75.6
77.0 
						

							May 25, 20056881096C74-B
5-52Troubleshooting Charts: Flowcharts
5.6.38 RX Back-End—Poor SINAD or No Audio (700–800 MHz)—Part 3 of 3
Figure 5-40.  RX Back-End—Poor SINAD or No Audio (700–800 MHz)—Part 3 of 3
No
3
3
32
DC
voltage at
R6007 =
0.0V?
Ye s No
Ye s Freq of
CLKOUT

						

							6881096C74-BMay 25, 2005
Troubleshooting Charts: Flowcharts5-53
5.6.39 Low or No RX Injection Signal (700–800 MHz)
Figure 5-41.  Low or No RX Injection Signal (700–800 MHz)
MAEPF-27810-O
Approx.
5V on
Q6762-C?START
Low or No RX
Injection Signal
No
No
Ye sNo
Ye s Ye s
Approx.
4.5V (–1V) on
Q6763-D?62
Ohms across
R6801?
Check RF path
from RX VCOReplace
Q6763 Check Q6762 and
DC Bias Circuitry;
replace if
necessary
Replace R6801
and Q6763 
						

							May 25, 20056881096C74-B
5-54Troubleshooting Charts: Flowcharts
5.6.40 Low or No TX Injection Signal (700–800 MHz)
Figure 5-42.  Low or No TX Injection Signal (700–800 MHz)
MAEPF-27811-O
Approx.
5.5 - 6V on
Q6764-C?START
Low or No TX
Injection Signal
No
Ye s
Check RF path
from TX VCOCheck Q6764 and
DC Bias Circuitry;
replace if
necessary
Approx.
5.5 - 6V on
Q6765-C?No
Ye sCheck Q6765 and
DC Bias Circuitry;
replace if
necessary
Approx.
8.5 - 9V on
Q6766-C?No
Ye sCheck Q6766 and
DC Bias Circuitry;
replace if
necessary 
						

							6881096C74-BMay 25, 2005
Troubleshooting Charts: Flowcharts5-55
5.6.41 No TX Audio (700–800 MHz)
Figure 5-43.  No TX Audio (700–800 MHz)
MAEPF-27814-O
1.0Vpp
at R6782 or
VN_T67770?No
Ye s
0.4Vpp
at TP6755 or
C6783?No
Ye sCheck deviation
tuning or replace
U6751 GOTO
Controller
Section
Check
synthesizer
loop filter
componentsNOTE:  After the modulated signal is coupled
through C6783 the signal is attenuated to levels
below 2mv making a measurement difficult for
most oscilloscopes. Inject a 2.0Vpp
1kHz tone into Mic
input and key radioSTART
No TX Audio
This Flow chart only checks the modulation
path of the FGU. Readings are typical and
can vary with deviation settings that are
programmed during tuning. 
						

							May 25, 20056881096C74-B
5-56Troubleshooting Charts: Flowcharts
5.6.42 TX or RX VCO Unlock (Fail 001) (700–800 MHz)—Part 1 of 2
Figure 5-44.  TX or RX VCO Unlock (Fail 001) (700–800 MHz)—Part 1 of 2
MAEPF-27812-O
Go to
Controller
troubleshooting
charts Ye s Frequency
Detected? Sniff Frequency
near TX or RX
VCO shield or
infection stringTX or RX VCO
Unlock (Fail 001)
No
Ye s
Check VCO
Control Voltage
at TP67598.2VDC
at Q6759
Collector?No
Ye s
3.0VDC
on pins 5, 36,
and 13 of
U6751?Check 9.3 Volt
supply path from
regulator U0950 in
Controller section
11.5VDC or
drifting?NoNo
Ye sCheck if VCO
is locked using
spectrum analyzer
12VDC
at Charge Pump
Capacitor
C6768?No
Ye sCheck Voltage
Multiplier
Circuitry Check Controller
Section and/or
ABACUS IC
U6000
Go to Transmitter
or receiver
Injection string
troubleshooting
chartsPlace an Inductive field probe
connected to a spectrum analyzer
near area to be sniffed.
Locked?
Ye s
3VDC
at pin 4 of
U6751?NoNo
Ye sCheck for short
on pin 4 to
controller or
replace U6751 Go to Transmitter
or receiver
Injection string
troubleshooting
charts
A 
						

							6881096C74-BMay 25, 2005
Troubleshooting Charts: Flowcharts5-57
5.6.43 TX or RX VCO Unlock (Fail 001) (700–800 MHz)—Part 2 of 2
Figure 5-45.  TX or RX VCO Unlock (Fail 001) (700–800 MHz)—Part 2 of 2
MAEPF-27818-O
Check 3 Volt
supply path from
Regulator U6750Refer to Chart to determine
which AUX output determines
active VCO. 3VDC
at pin 5 of
U6750?NoCheck 5 Volt
supply path from
regulator U0505
Unlock
RX or
TX?TX
RX Ye s
Aux 3
or 4 at 3.0VDC
for RX?No
No Ye sCheck
U6751
Check
U67558.2VDC
at TP6753 or
TP6751?
Ye sCheck
Q6756 or
Q6760Aux 1
or 2 at 3.0VDC
for TX?No
No Ye sCheck
U6751
Check
U67548.2VDC
at TP6767 or
TP6761?
Ye sCheck
Q6767 or
Q6755
A 
						

							May 25, 20056881096C74-B
5-58Troubleshooting Charts: Flowcharts
5.6.44 RF Power Amplifier (RFPA)—No or Low TX Power Output (700–800 MHz)—
Part 1 of 5
NOTE:For each flowchart step in which reference is made to a note, be sure to refer to that specific 
note (located on page 61 of this flowchart) for guidance in performing the actual 
troubleshooting procedure. Also, RFPA DC voltages are shown in Table 5-7 on page 5-62.
Figure 5-46.  RF Power Amplifier (RFPA)—No or Low TX Power Output (700–800 MHz)—Part 1 of 5
Read General
Notes before
proceeding. Read
specific notes as
indicated
Check battery
cable, mic, and
control head
connections
START
Continuous red light
while mic button is
depressed?GOTO Sythesizer-
No Transmit
Chart ?
Tune power with
Tuner?
(see help text)
No
Yes
Tune current limit
with Tuner
(see help text) Yes
No
TX injection power
 less than 2 mW?
(Note 1)GOTO Sythesizer-
No or Low Tx
Injection
Chart ? Yes
K9.1V
 present
 at Q0952, pin 1 in
power control section
when transmitter is
 keyed?
No
GOTO Power
Control - No K9.1V
Chart ?
RFPA_CNTRL
voltage (VN_B6503)
less than 5.0V when 
 transmitter is
 keyed?
YesNo
GOTO Power
Control - No or low
RFPA_CNTRL
Chart ? No
U6500 drain biases
voltages per Table 1?
(Note 3)
Yes
No
Check/repair/
replace defective
parts
Yes
No
A
Is U6500,
 VCNTRL resistance <
 1 kOhms?
(Note 2)YesRepair/replace
U6500
No
Is U6500,
 RFOUT and VD1
resistance <
 1 MOhms?
(Note 4)Yes
Repair/replace
U6500
MAEPF-27929-O 
						

							6881096C74-BMay 25, 2005
Troubleshooting Charts: Flowcharts5-59
5.6.45 RF Power Amplifier (RFPA)—No or Low TX Power Output (700–800 MHz)—
Part 2 of 5
Figure 5-47.  RF Power Amplifier (RFPA)—No or Low TX Power Output (700–800 MHz)—Part 2 of 5
Defective parts
 in matching network
between Q6520 and
Q6540-1?
(Note 9)Repair/replace
defective parts Yes
No
Defective parts
 in matching network
between Q6500 and
Q6520?
(Note 5)Repair/replace
defective parts Yes
Q6520 bias voltages
 as per Table 1?
(Note 6)
No
Check/repair/replace
defective parts or
GOTO Power Control
- No/low VGBIAS
Chart
Is Q6520,
 gate resistance <
 1 MOhms?
(Note 7)YesRepair/replace
Q6520 and retune
gate bias via
Tuner
 (see help text)
NoNo
Yes
Is Q6520,
 drain resistance <
 1 MOhms?
(Note 8)Yes
No
Q6540-1 bias
voltages as per Table 1?
(Note 10)
Defective parts
in matching network
between Q6540-1 and
antenna switch?
(Note 13)
Antenna switch
 bias voltages as per
Table 1?
(Note 14)
Repair/replace
defective parts
Is Q6540-1,
 gate resistance <
 1 MOhms?
(Note 11)Yes
No
Is Q6540-1,
 drain resistance <
 1 MOhms?
(Note 12)Yes
No
Repair/replace
defective parts NoNo
Yes
YesYes
No
Repair/replace
Q6520 and retune
gate bias via
Tuner
 (see help text)
Check/repair/replace
defective parts or
GOTO Power Control
- No/low VGBIAS
Chart
Repair/replace both
Q6540 and Q6541
(see General Notes)
and retune gate bias
via Tuner
 (see help text)
Repair/replace both
Q6540 and Q6541
(see General Notes)
and retune gate bias
via Tuner
 (see help text)
B
A
MAEPF-27930-O 
						

							May 25, 20056881096C74-B
5-60Troubleshooting Charts: Flowcharts
5.6.46 RF Power Amplifier (RFPA)—No or Low TX Power Output (700–800 MHz)—
Part 3 of 5
Figure 5-48.  RF Power Amplifier (RFPA)—No or Low TX Power Output (700–800 MHz)—Part 3 of 5
YesDefective parts in
antenna switch?
(Note 15)Repair/replace
defective parts
Defective parts in
 harmonic filter?
(Note 16)
No
Yes
Repair/replace
defective parts
No
Defective parts in
 power detector?
(Note 17)Yes
Repair/replace
antenna connectorContinuity check
 fails from R6740 and
the antenna connector
external coax?
No
Yes
Repair/replace
defective parts
B
MAEPF-27931-O
Go to the
Controller GPIO
Section
No