Motorola Astro Digital Mobile Radio Xtl5000 Detailled 6881096c74 B Manual

6881096C74-BMay 25, 2005
Troubleshooting Charts: Flowcharts5-41
5.6.27 RF Power Amplifier (RFPA)—No or Low TX Power Output (380–470 MHz and 
450–520 MHz)—Part 2 of 5
Figure 5-31.  RF Power Amplifier (RFPA)—No or Low TX Power Output (380–470 MHz and 450–520 MHz)—
Part 2 of 5
Defective parts
 in matching network
between Q5502 and
Q5503?
(Note 9)Repair/replace
defective parts Yes
No
Defective parts
 in matching network
between U5501 and
Q5502?
(Note 5)
Repair/replace
defective parts Yes
Q5502 bias voltages...

May 25, 20056881096C74-B
5-42Troubleshooting Charts: Flowcharts
5.6.28 RF Power Amplifier (RFPA)—No or Low TX Power Output (380–470 MHz and 
450–520 MHz)—Part 3 of 5
Figure 5-32.  RF Power Amplifier (RFPA)—No or Low TX Power Output (380–470 MHz and 450–520 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...

6881096C74-BMay 25, 2005
Troubleshooting Charts: Flowcharts5-43
5.6.29 RF Power Amplifier (RFPA)—No or Low TX Power Output (380–470 MHz and 
450–520 MHz)—Part 4 of 5
Specific Notes:
1. Remove C5508 and solder the center conductor of a small 50-ohm, coaxial cable to TP5502. 
Solder ground to the gold shield track adjacent to TP5502. Attach an RF milliwatt meter, key 
the transmitter, and measure TX_INJ power. Then, remove the coaxial cable and replace 
C5508. Remove the solder added to shield track.
2....

May 25, 20056881096C74-B
5-44Troubleshooting Charts: Flowcharts
5.6.30 RF Power Amplifier (RFPA)—No or Low TX Power Output (380–470 MHz and 
450–520 MHz)—Part 5 of 5
Table 5-6.  RFPA DC Voltages
DescriptionLocationVoltage (Vdc) 
(380–470 MHz)Voltage (Vdc) 
(450–520 MHz)
A+ = 13.6 Vdc
U5501, VD1 U5501 pin 14 9.0–9.3 9.0–9.3
U5501, RFOUT U5501 pins 6 and 7 9.0–9.3 9.0–9.3
Q5502 Gate Bias R5516/C5525 
node1.8–2.0 1.8–2.1
Q5502 Drain Bias L5508/R5517
Node9.0–9.3 9.0–9.3
Q5503 Gate Bias 1 R5520/C5539...

6881096C74-BMay 25, 2005
Troubleshooting Charts: Flowcharts5-45
5.6.31 RFPA Power Control—No VGBIAS (380–470 MHz and 450–520 MHz)
Figure 5-33.  RFPA Power Control—No VGBIAS (380–470 MHz and 450–520 MHz)
Read General
Notes before
proceeding. Read
specific notes as
indicated
START
NoYes
Repair/replace
U0960
No
No/low 
Q5503 pin 7 
VGBIAS1?
No/low 
Q5503 pin 6 
VGBIAS2?
Remove U0960.
TP0937 voltage
 2.6-2.8 V? Yes
Remove U0960.
TP0939 voltage
 2.6-2.8 V? Yes
Remove U0960.
TP0941 voltage
 2.0-2.2 V? No...

May 25, 20056881096C74-B
5-46Troubleshooting Charts: Flowcharts
5.6.32 No 16.8 MHz Reference Oscillator Frequency (700–800 MHz)
Figure 5-34.  No 16.8 MHz Reference Oscillator Frequency (700–800 MHz)
MAEPF-27813-O
U6752DC Voltages
Pin 1
Pin 2
Pin 3
Pin 4
Pin 5No connection
1.5
Ground
1.5
3
>800mVpp
16.8MHz? Probe pin 3
of Y6750 for
16.8MHzSTART
No 16.8MHz
Reference
No
Ye s
>800mVpp
at TP6764?No
Ye sCheck
C6817Replace
Y6750 3.0VDC
at pin 1 of
Y6750?No
Ye sCheck 3.0V
regulator path
from U6750
>500mVpp
at...

6881096C74-BMay 25, 2005
Troubleshooting Charts: Flowcharts5-47
5.6.33 Poor RX Sensitivity or No RX Audio (700–800 MHz)—Part 1 of 2
Figure 5-35.  Poor RX Sensitivity or No RX Audio (700–800 MHz)—Part 1 of 2
MAEPF-27875-O
Poor Rx
Sensitivity or no
Rx audio
Measure Transceiver
Sinad by injection
signal at antenna portYe s
Ye s3kHz FM Deviation
1kHz Audio  tone
Sinad
< - 119.1dBm?
Check RF level at
Mixer LO injection port
(U6251 Pin 3 side 1)Receiver
is working
properly
NoYe s
Good?
1Check Q6350,
Q6251,...

May 25, 20056881096C74-B
5-48Troubleshooting Charts: Flowcharts
5.6.34 Poor RX Sensitivity or No RX Audio (700–800 MHz)—Part 2 of 2
Figure 5-36.  Poor RX Sensitivity or No RX Audio (700–800 MHz)—Part 2 of 2
MAEPF-27874-O
1
Inject a standard FM test
signal into the antenna port.
Use a spectrum analyzer and
high-impedance RF probe to
measure the signal at TP6253.

6881096C74-BMay 25, 2005
Troubleshooting Charts: Flowcharts5-49
5.6.35 RX IF—Poor SINAD or No Audio (700–800 MHz)
Figure 5-37.  RX IF—Poor SINAD or No Audio (700–800 MHz)
MAEPF-27809-O
Level
is +4dB
referenced to the
RF input
level?No
No No Ye s
Measure the IF
signal level
(73.35MHz)
at TP6350 Measure the IF
signal level
(73.35MHz)
at TP6252
Refer to
troubleshooting
flow diagram for
Receiver Front End
Level
is +20dB
relative to the RF
input level?No
Ye s
Voltage
level of
>~5.0V at Q6350
Collector
(pin...

May 25, 20056881096C74-B
5-50Troubleshooting Charts: Flowcharts
5.6.36 RX Back-End—Poor SINAD or No Audio (700–800 MHz)—Part 1 of 3
Figure 5-38.  RX Back-End—Poor SINAD or No Audio (700–800 MHz)—Part 1 of 3
MAEPF-27806-O
Is the
IF level at
TP6350~+20dB
relative to the
RF input?No
No
No
NoNo No
Ye s
Ye sYe s
Ye s Ye s
Signal
present?Voltage
level of >~3.5V
at Q6000
Collector?
Voltage
level of ~2.15V
at Q6000 Base
(pin 1)? Measure Second LO
at C6026, top side
towards Abacus  III
(U6000) pinRefer back to...