Motorola APX 5000 Service Manual page 169

Troubleshooting Charts: PA Failure
PA Failure – Page 8 (UHF1 ALC)
Replace U1601
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.
Replace log amp, U1105,
else U1112, else check
R1106 for 17 +/- 1 Ohm
Yes
U1127 pin 4
approximately
Replace U1142
1.10 +/- 0.05V
Yes
Replace U1126 and
U1127
8
Remove shield SH1 & measure
PA control voltage at U1601 pin 4
Measure voltage at
U1601 pin 1
Yes
No
VC_OFFSET low,
U1601 pin 1
remove shield SH10
2.2V +/- 0.6V?
Yes
No
Replace U1132
Yes
Measure thermal cutback
circuit output at U1113,
U1114, and U1121
Yes
Pin 4 of U1113,
U1114, & U1121
at 0V (logic low)?
No
Check temp sensor
U1103, else U1148
Yes
Measure output
pin 4 of U1130
Yes
U1130 pin 4
No
approximately
?
1.10 ± 0.05V
No
U1133 pin 3 4.1V
U1133 pin 6
+/- 0.6?
about 5V?
Yes
Remove shield SH6 and
R1181 close to 5V?
measure U1142 pin4
Measure voltage divider
No
U1142 pin 4
at power tuning DAC, top
1.00V +/- 0.3V?
of R1121
Yes
R1121 around
Measure TP101
2.45 V +/- 0.15?
voltage
ANA_CTRL_ISET low. Check R1160
No
TP101
for wrong value, else check connector
closed to 1.5V?
P101, or MAKO IC on Vocon
No
U1101 Pin 1 Transmitter PA overcurrent condition,
< 1.3V? else check U1101, R1103.
Yes
Replace U1129, U1130
PA_OFFSET low,
Yes
check U1125 pin 1
for approx. 1V, else
replace U1133
No
No
Measure TP120
No
TP120 1.8V?
Yes
Replace U1139 or
associated logic
No
Power tuning is low, else
replace U1125, else U1137,
U1138.
5-63
Check P101 or VOCON
signal DIG_CTRL_IO49