Motorola APX 7000 Detailed Service Manual page 161

Troubleshooting Charts: PA Failure
PA Failure – Page 9 (UHF2 PA)
9
Measure TX current
at UHF2 test
frequencies.
Is current less
than 350 mA?
No
Is current
Yes
Replace Q1501
approximately
500 mA?
No
Is current
greater than or
close to 2A?
Yes
Use a spectrum
analyzer and high-
impedance RF probe.
Measure RF_IN_1 at
C1500.
Yes
See FGU
No
Is the frequency
troubleshooting
correct?
charts.
Yes
Check U1110 and
Is the power
No
see FGU
level about 3
troubleshooting
dBm?
charts.
Yes
Measure power at
C1521.
Is the power
No
appoximately 37 Replace U1500.
dBm?
Measure power at
C1707, and calculate
harmonic filter loss.
Yes
Repair any issues
No
Is the loss less
with 1700 series parts
than 1 dB?
in the harmonic filter.
Yes
PA and harmonic
filter are functioning
properly.
If power issue is not
resolved.
4
Yes
Measure DC voltage
at pin 4 of U1501
No
Is voltage
approximate 6 V?
Yes
Measure DC voltage
at pin 5 of U1501
Is voltage
near 7.5 V
No
Yes
With the radio in RX
mode, measure the
DC voltage on
both pins of L1500
Is voltage
near 7.5 V
on both side?
Yes
No
With the radio in RX
mode, measure the
DC voltage on the
drain of Q1500.
Is voltage
near 7.5 V?
No
Yes
With the radio in RX
mode, measure the
resistance on the
node shared by
C1512 and C1511.
No
Is the resistance
near 9.9K Ohms?
Yes
In TX mode, measure
the voltage on pin 4
of U1501.
Is the voltage Yes
near 6 V?
No
Yes
Is the voltage
10
below 4 V?
No
If the voltage is between 4 and 5.5 V then
the control loop should be working and
power should be available. Check the
coaxial cables and surface mounted coaxial
connectors.
Were the
Yes
3
connections
OK?
No
Replace cables, or
connectors J101 or
J102.
Measure voltage at
pin 5 of U1501
Measure voltage at
Is voltage
No
pin 3 of Q1101(UHF2/7800) or
approximate 7 V?
pin 3 of Q1102 ( UHF2/VHF) or
pin 3 of Q1102(UHF1/UHF2)
Yes
Replace U1501
Measure voltage at
pin 1 of Q1101(UHF2/7800) or
pin 1 of Q1102 (UHF2/VHF) or
pin 1 of Q1102(UHF1/UHF2)
Measure voltage at
No
Is voltage
pins 2 and 3 (UHF2/7800) or
near 3 V
pins 7 and 6 (UHF2/VHF) or
pins 7 & 6 (UHF1/UHF2) of
U1119. They should be
Yes
5 V and 2.775 V respectively.
Trace voltages and check
for solderability issues on
R1102, Q1101, and Q1103.
Replace parts as necessary.
Check E1101 for
Is there No
solderability issues
7.5 V on C1102?
and replace as necessary
Yes
Check L1500 for
solderability issues and
replace as necessary.
Check L1505 under
sheild SH10 for
solderability issues
and replace as necessary.
.
Check resistors R1503, R1504,
If resistance is very low, in the
R1502, R1500,R1506 and
100's of ohms,and there are
R1505 for resistance and
no issues with the resistors
solderability issues and replace
then there is a gate short on the PA.
as necessary.
Clear short or replace Q1500.
Is TX current just The PA and Driver are likely
Yes
above standby
damaged. Replace Q1500
current?
No
Is the TX current
Yes
damaged. Replace
between 300
and 900 mA?
No
Lift shield SH10 and check
for solderability or part
Yes
Is the TX current
issues on all 1500 series
above 900 mA?
parts. Replace parts as
Yes
Is voltage
approximate 0 V?
No
Measure voltage at
pin 1 of Q1101 (UHF2/7800) or
pin 1 of Q1102 (UHF2/VHF) or
pin 1of Q1102 (UHF1/UHF2)
Yes
Is voltage
greater than 1.5 V?
No
Measure voltage at
pins 2 and 3 (UHF2/7800) or
pins 7 and 6 ( UHF2/VHF) or
pins 7 and 6 (UHF1/UHF2)
of U1119.
Are
pins 2 and 3 or
Yes
pins 7and 6
close to 5V & 2.775V
respectively?
No
10
and U1500.
The PA is likely
Q1500.
If no issues found, lift shield
SH13 and check for solderability
or part issues on all 1200 series
parts. Replace parts as
necessary.
necessary.
If power issue is not
resolved.
5-57
Replace
Q1103 (UHF2/7800) or
Q1104 ( UHF2/VHF) or
Q1104 (UHF1/UHF2)
Replace
Q1101(UHF2/7800) or
Q1102 (UHF2/VHF) or
Q1102(UHF1/UHF2)
Replace
U1119
4