Motorola APX 5000 Service Manual page 167

Troubleshooting Charts: PA Failure
PA Failure – Page 6 (7/800 ALC)
PA_OFFSET low,
check U1125 pin 1
for approx. 1V, else
replace U1133
Measure TP120
TP120 1.8V?
Yes
Replace U1139 or
associated logic
Replace U1129, U1130
Remove SH9A & measure
PA control voltage at U1001 pin 4
Measure voltage at U1001 pin 1
No
U1001 pin 1
VC_OFFSET low,
remove SH12
2.2V +/- 0.3V?
Yes
U1133 pin 6
about 5V?
No
Yes
U1133 pin 3 4.5V
+/- 0.5?
No
Yes
No
Remove SH11 and
R1181 5V?
measure U1142 pin4
No
Check P101 or VOCON
signal DIG_CTRL_IO49
Measure voltage divider
at power tuning DAC,
Power tuning is low, else
No
replace U1125, else U1137,
U1138.
Measure TP101 voltage
Yes
Measure output pin 4
of U1130
Yes
U1130 pin 4 U1127 pin 4
approximately approximately
1.15v? 1.15V?
No
Replace U1127,
Yes
else U1126
U1101 Pin 1
< 1.3V?
No
Transmitter PA overcurrent condition,
else check U1101, R1103.
6
Yes
Replace U1001
TX in Current control mode?
Yes
U1131, pin 4
is 5V?
No
Replace U1132
Yes
U1142 pin 4
Measure thermal cutback circuit
1.15V +/- 0.01V?
output at U1113, U1114, and U1121
No
top of R1121
R1121 around
1.15V +/- 0.015?
Yes
ANA_CTRL_ISET low. Check R1160
No
for wrong value, else check connector
TP101 1.5V?
P101, or MAKO IC on Vocon
Yes
Replace U1142
No
TX is in current control mode, else PA is
saturated. Check SAT Reference tuning
per 12M to ensure tuning is not low.
Pin 4 of U1113,
Yes
Replace log amp, U1105,
U1114, & U1121
else U1112, else check
at 0V (logic low)?
R1106 for 17 +/- 1 Ohm
No
Check temp sensor
U1103, else U1148
5-61