Motorola APX 5000 Service Manual page 163

Troubleshooting Charts: PA Failure
PA Failure – Page 2 (VHF PA)
Check L906 under sheild SH9B
for solderability issues and
replace as necessary.
2
Remove shield SH9A. On a spectrum
analyzer measure input frequency
and power level at C901.
Is frequency and No
spectrum of the
signal OK?
Yes
Is power level No
above 0 dBm?
Yes
Measure DC voltage
on C903 and C905.
Was voltage No
near 7.5 V?
Yes
With the radio in RX mode,
measure the DC voltage
on both pins of L903.
Was voltage
near 7.5 V on
both sides?
Yes
With the radio in RX mode,
measure the DC voltage
on the drain of Q901.
No
Was voltage
near 7.5 V?
Yes
With the radio in RX mode,
measure the resistance on
the node shared by C916
and R906.
Is
the resistance No
near 9.4k
Ohms?
Yes
In TX mode, measure the
voltage on pin 4 of U901.
Is the voltage
Yes
near 6 V?
Yes
Is the voltage
5
below 4 V?
No
If the voltage is between 4 and 5.5V
then the control loop should be
working and power should be
available. Check the coaxial cables
and surface mounted coaxial connectors.
Were the
Yes
connections
OK?
No
Replace cables, or
connectors J101 or
J102.
See FGU
troubleshooting charts.
Was the change
Measure power level
in power level
at pin 5 of U1110.
more than 2 dB
higher?
Check voltage on pins 4 and
6 of U1110, pin 4 should be
near 0 V and pin 6 should
be near 2.775V.
Were the
voltages
Measure voltage correct?
at pin 1 of Q1101.
Replace U1110.
Was voltage No
near 3 V?
Measure inputs on pins 2
and 3 to AND gate U1119.
Pin 2 and 3 should be 5
Yes
and 2.775V respectively.
Trace voltages and check
for solderability issues on
R1102, Q1101, and Q1103.
No Replace parts as necessary.
Is there 7.5 V on
C908?
Check L903 for solderability
issues and replace as
necessary.
Check resistors R901, If resistance is very low, in the
R902, R903, R904, and 100's of ohms,and there are no
R905 for resistance and issues with the resistors then
solderability issues and there is a gate short on the PA.
replace as necessary.
Clear short or replace Q901.
Is
TX current
Yes The PA and Driver are likely damaged.
just above
Replace Q901 and U902.
stanby current?
No
Is
The PA is likely damaged.
the TX current Yes
between 300 and
Replace Q901.
900 mA?
No
Lift shield SH9B and check
Is
for solderability or part issues
Yes
the TX current
on all 900 series parts.
above 900 mA?
Replace parts as necessary.
If no issues found, lift shield SH12
and check for solderability or part
issues on all 1200 series parts.
Replace parts as necessary.
3
If power issue is not
See FGU
No
troubleshooting
charts.
Yes
See FGU
No
troubleshooting
charts.
Yes
Check E1101 for
No
solderability issues and
replace as necessary.
Yes
resolved.
4
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