Motorola APX 1000 Detailed Service Manual page 161

Troubleshooting Charts: PA Failure
PA Failure – Page 4 (900 MHz PA)
4
Measure TX current
at 900MHz test
frequencies.
Is current less
than 350 mA?
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 C1001.
Yes
See FGU
No
Is the frequency
troubleshooting
correct?
charts.
Yes
See FGU
No
Is the power level
troubleshooting
about 3 dBm?
charts.
Yes
Measure power at
C1022.
Is the power
No
appoximately 37
Replace Q1001.
dBm?
Yes
Measure power at
C2304
No
Is the power Check D2303
appoximately 37
positive node
dBm?
voltage
Measure power at
C1411
Is the voltage
near 7.0V
Is the power
appoximately 37
Replace D2303
dBm?
Yes
Check power out at
C1122 and for any
process issue
Measure DC voltage
at Pin 4 of U1001
Is voltage
Yes
approximately 6V
Replace Q1001
at DAC=4095?
No
Measure voltage at
pin 5 of U1001.
Is voltage Yes
approximately
Replace U1001.
7V?
No
Measure voltage at
pin 3 of Q1101.
Yes
Is voltage
approximately Replace Q1103.
0V?
No
Measure voltage at
pin 1 of Q1101.
Yes
Is voltage greater
Replace Q1101.
than 1.5 V?
No
5
No
Check pin 3 and pin
2 of Q2301
Yes
No
Is pin 3 of
Q2301=Raw B+ Check continuity of
and pin 2 = 3.0V
R2305 and L2302
Yes
Replace Q2301
Measure DC voltage
at Pin 5 of U1001
No
Was voltage Measure voltage at
near 7.5 V? pin 1 of Q1101.
Yes
With the radio in RX
mode, measure the
DC voltage on both
pins of L1003.
Was voltage near No
Is there 7.5 V
7.5 V on both
on C1008?
sides?
Yes
Yes
With the radio in RX Check L1003 for
mode, measure the solderability issues and
DC voltage on the replace as necessary.
drain of Q1001.
Check L1007 under sheild
No
Was voltage SH1 for solderability
near 7.5 V? issues and replace as
necessary.
Yes
With the radio in RX
mode, measure the
resistance on the
node shared by
R1006 and R1005.
Check resistors R1001,
No
R1002, R1003, R1004,
Is the resistance
and R1005 for resistance
near 9.4k Ohms?
and solderability issues
and replace as necessary.
Yes
In TX mode,
measure the voltage
on pin 4 of U1001.
Yes
Is TX current just
Is the voltage
above standby
near 6 V?
current?
Is the TX current
between 300 and
900 mA?
Is the TX current
above 900 mA?
Yes
Is the voltage
5
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 D2303
positive node voltage
No
Is the voltage
Check pin 3 and pin
near 7.0V
2 of Q2301
Yes
Replace D2303
Is pin 3 of
Q2601=Raw B+
and pin 2 = 3.0V
Yes
Replace Q2301
Measure the logic
No
inputs of TXH_1
Was voltage
from R1111 and
near 3 V?
TX_INH from U1138
Yes
Trace voltages and check for solderability
issues on R1102, Q1101, and Q1103.
Replace parts as necessary.
No Check E1101 for
solderability issues and
replace as necessary.
If resistance is very low, in the
100's of ohms,and there are no
issues with the resistors then
there is a gate short on the PA.
Clear short or replace Q1001.
Yes
The PA and Driver are
likely damaged. Replace
Q1001 and U1002.
The PA is likely
Yes
damaged. Replace
Q1001.
Lift shield SH1 and check If no issues found, lift shield
Yes for solderability or part SH8 and check for solderability
issues on all 900 series or part issues on all 1200
parts. Replace parts as series parts. Replace parts as
necessary.
No
Check continuity of
R2305 and L2302
5-63
necessary.