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...

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...

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...

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...

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...

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...

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...

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...