Motorola APX 7000 Detailed Service Manual page 162

5-58
PA Failure – Page 10 (UHF2 ALC)
Replace U1501
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
10
Remove SH5 & measure
PA control voltage at U1501 pin 4
Measure voltage at
pin 3 (UHF2/7800) or
pin1 (UHF2/VHF) or
pin1 (UHF1/UHF2) of U1145
Yes
No
VC_OFFSET low,
U1145 pin 1 or pin 3
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
Remove SH11 & measure
output pin 4 of U1130
Yes
U1130 pin 4
No
approximately
? 1.10±0.05V?
Notes
remove SH13
No
U1133 pin 6
U1133 pin 3 4.1V
about 5V?
Yes
Remove SH9 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
TP101 No
for wrong value, else check connector
closed to `1.5V?
No
U1101 Pin 1 Transmitter PA overcurrent condition,
< 1.3V? else check U1101, R1103.
Yes
Replace U1129 and
U1130
Troubleshooting Charts: PA Failure
PA_OFFSET low,
Yes
check U1125 pin 1
for approx. 1V, else
+/- 0.6?
replace U1133
No
No
Measure TP120
TP120 1.8V?
Yes
Replace U1139 or
associated logic
No
Power tuning is low, else
replace U1125, else U1137,
U1138.
P101, or MAKO IC on Vocon
No
Check P101 or VOCON
signal DIG_CTRL_IO49