Pa Failure - Motorola APX 3000 Detailed Service Manual

Troubleshooting Charts: PA Failure
PA Failure – Page 1 (UHF1/UHF2)
1
Measure TX current
at UHF1 test
frequencies
Is current less
than 350mA?
No
Is current
Yes
approximately
500mA?
No
Is current greater
than or close to
2A?
Yes
Use a spectrum
analyzer and high-
impedance RF
probe. Measure
RF_IN_1 at C1601.
Yes
No
Is the frequency
correct?
Yes
Is the power No
level about 3 dBm?
Yes
Measure power at
C1625
Is the power
No
approximately
37 dBm?
Yes
Measure power at
C2604
Is the power
No
approximately
37 dBm?
Measure power at
C1822
Is the power
approximately
37 dBm?
Yes
Check power out at
C1122 and any
process issue
Yes
Measure DC voltage
at pin 4 of U1601
Is voltage
Yes
approximately 6V
at DAC=4095?
Replace Q1601
No
Measure voltage at
pin 5 of U1601
Is voltage
Yes
approximately
7V?
No
Measure voltage at
pin 3 of Q1101
See FGU
troubleshooting
Is voltage
Yes
charts
approximately
0V?
No
See FGU
Measure voltage at
troubleshooting
pin 1 of Q1101
charts
Yes
Is voltage greater
than 1.5V?
No
4
Replace Q1601
Check D2603
positive node
voltage
No
Check pin 3 and
Is the voltage
pin 2 of Q2601
near 7.0V?
Yes
Replace D2603
Is pin 3 of
No
Check continuity of
Q2601=Raw B+
R2605 and L2602
and pin 2=3.0V
Yes
Replace Q2601
Measure DC voltage
at pin 5 of U1601
No
Measure voltage at
Was voltage
pin 1 of Q1101
near 7.5V?
Yes
With the radio in RX
mode, measure the
Replace U1601
DC voltage on both
pins of L1603
Was voltage No
near 7.5V on
both sides?
Yes
With the radio in RX
solderability issues and
Replace Q1103 mode, measure the
replace as necessary
DC voltage on the
drain of Q1601
Check L1606 under shield
No
Was voltage
issues and replace as
near 7.5V?
Yes
Replace Q1101
With the radio in RX
mode, measure the
resistance on the
node shared by
C1616 and R1605
Check resistors R1601,
No
R1602, R1603, R1604,
Is the resistance
and R1605 for resistance
near 9.4 kOhms?
and solderability issues
and replace as necessary
Yes
In TX mode,
measure the voltage
on pin 4 of U1601
Yes
Is the voltage
near 6V?
Yes
Is the voltage
4
below 4V?
No
If the voltage is between 4 and 5.5V then
the control loop should be working and
power should be available. Check D2603
positive node voltage.
No
Check pin 3 and
Is the voltage
pin 2 of Q2601
near 7.0V?
Yes
Replace D2603
Is pin 3 of
Q2601=Raw B+
and pin 2=3.0V
Replace Q2601
No Measure the logic
Was voltage
inputs of TXH_1
near 3V?
from R1111 and
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
Is there 7.5V
solderability issues and
on C1608?
replace as necessary
Yes
Check L1603 for
SH1 for solderability
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 Q1601.
The PA and Driver are
Is TX current just
Yes
likely damaged. Replace
above standby
Q1601 and U1602.
current?
The PA is likely
Is the TX current Yes
damaged. Replace
between 300 and
Q1601.
900mA?
Lift shield SH1 and check
Is the TX current Yes
for solderability or part
above 900mA?
issues on all 900 series
parts. Replace parts as
necessary.
No
Check continuity of
R2605 and L2602
Yes
5-51
If no issues found, lift shield
SH8 and check for solderability
or part issues on all 1200
series parts. Replace parts as
necessary.