Motorola APX 5000 Service Manual page 170

5-64
PA Failure – Page 9 (UHF2 PA)
9
Measure TX current
at UHF2 test
frequencies.
Is current less
than 350 mA?
No
Is current
Yes
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
No
Is the frequency
correct?
Yes
Is the power
No
level about 3
dBm?
Yes
Measure power at
C1521.
Is the power No
about 37 dBM?
Measure power at
C1707, and calculate
harmonic filter loss.
Yes
No
Is the loss less
than 1 dB?
Yes
PA and harmonic
filter are functioning
properly.
If power issue is not
resolved.
4
Yes
Measure DC voltage
at pin 4 of U1501
Replace Q1500
Is voltage
approximate 6 V?
Yes
Measure DC voltage
at pin 4 of U1501
Was voltage
near 7.5 V
Yes
With the radio in RX
See FGU
mode, measure the
troubleshooting
DC voltage on
charts.
both pins of L1500
Check U1110 and
Was voltage
see FGU
near 7.5 V?
troubleshooting
charts.
Yes
With the radio in RX
mode, measure the
resistance on the
node shared by
C1511 and R1502.
Replace U1500.
Is the resistance
near 9.4k
Ohms?
Yes
In TX mode, measure
the voltage on pin 4
of U1501.
Repair any issues
with 1700 series parts
in the harmonic filter.
Is the voltage
near 6 V?
No
Is the voltage
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
connections
OK?
No
Replace cables, or
connectors J101 or
J102.
No
Measure voltage at
pin 5 of U1501
Is voltage
No
Measure voltage at
approximate 7 V?
pin 3 of Q1101.
Yes
Replace U1501
Measure voltage
No
at pin 1 of Q1101.
Measure inputs
No
Was voltage
on pins 2 and 3 to
near 3 V
AND gate U1119.
Pin 2 and 3 should
be 5 and 2.775V
Yes
respectively.
Trace voltages and check
for solderability issues on
R1102, Q1101, and Q1103.
Replace parts as necessary.
Check L1505 under sheild
No
SH5 for solderability issues
and replace as necessary.
Check resistors R1502,
No R1503, R1504, R1505 and 100's of ohms,and there are no
R1506 for resistance and
solderability issues and there is a gate short on the PA.
replace as necessary.
Is TX current just
Yes
Yes
above standby
current?
Is the TX current
Yes
between 300
and 900 mA?
Yes
10
Yes
Is the TX current
above 900 mA?
Yes
3
Troubleshooting Charts: PA Failure
Yes
Is voltage
approximate 0 V?
No
Measure voltage at
pin 1 of Q1101.
Is voltage
greater than 1.5 V?
No
Measure voltage at
pin 2 and 3 of U1119
Are
Pins 2 and 3,
Yes
close to 5V and 2.775V
respectively?
No
10
If resistance is very low, in the
issues with the resistors then
Clear short or replace Q1500.
The PA and Driver are likely
damaged. Replace Q1500
and U1500.
The PA is likely
damaged. Replace
Q1500.
Lift shield SH5 and check
If no issues found, lift shield
for solderability or part
SH10 and check for solderability
issues on all 1500 series
or part issues on all 1200 series
parts. Replace parts as
parts. Replace parts as
necessary.
If power issue is not
Replace
U1501
Replace
U1119
necessary.
resolved.
4