Motorola APX 5000 Service Manual page 166

5-60
PA Failure – Page 5 (VHF ALC)
No
Check P101 or VOCON
signal DIG_CTRL_IO49
Replace log amp, U1105,
else U1112, else check
R1106 for 17 +/- 1 Ohm
5
Remove SH9A & measure PA
PA control voltage at U901 pin 4
Measure voltage at
U901 pin 1
U901 pin 1
2.2V +/- 0.3V?
VC_OFFSET low,
remove SH12
No
Measure TP120
R1181 5V?
Yes
TP120 1.8V?
Remove SH11 and
measure U1142 pin4
Yes
Replace U1139 or
associated logic
U1142 pin 4
about 1.1V?
Measure thermal cutback circuit
output at U1113, U1114, and U1121
Yes
Pin 4 of U1113,
U1114, & U1121
at 0V (logic low)?
Check temp sensor
U1103, else U1148
Replace U1142
Yes
Replace U901
No
Yes
U1133 pin 6
about 5V?
No
No
U1133 pin 3 3.5V
+/- 0.5?
Yes
PA_OFFSET low, check
U1125 pin 1 for approx. 1V,
else replace U1133
Measure voltage divider
No
at power tuning DAC, top
Yes
Measure TP101 voltage
No
Measure output
pin 4 of U1130
Yes Yes
U1127 pin 4
approximately
1.1V?
No
Replace U1127,
else U1126
Replace U1129, U1130
Troubleshooting Charts: PA Failure
TX in Current control mode?
U1131, pin 4
is 5V?
Yes
TX is in current control mode, else PA is
saturated. Check SAT Reference tuning
per 12M to ensure tuning is not low.
of R1121
Power tuning is low, else
No
R1121 around
replace U1125, else U1137,
1.1V?
U1138.
Yes
ANA_CTRL_ISET low. Check R1160
No
for wrong value, else check connector
TP101 1.5V?
P101, or MAKO IC on Vocon
Yes
U1130 pin 4
approximately
1.1v?
No
No
Transmitter PA overcurrent condition,
U1101 Pin 1
else check U1101, R1103.
< 1.3V?
Yes
No
Replace U1132