Motorola APX 1000 Detailed Service Manual page 162

5-64
PA Failure – Page 5 (ALC)
5
Remove SH15 and measure
PA control voltage at
U901 for VHF,
U1601 for UHF1/UHF2 and
U1001 for 700/800/900 MHz
pin 4
VC_OFFSET low,
remove SH6
Yes
U1133 pin6
about 5V?
No
PA_OFFSET low,
Yes
U1133 pin 3
check U1125 pin 1
4.1V +/- 0.6V?
for approx. 1V, else
replace U1133
No
No
R1180 close to 5V?
Measure TP6107
Yes
TP6107 1.8V?
Yes
Remove SH3 and
Replace U1139 or
measure U1142 pin4
associated logic
Yes
U1142 pin4
1.00V +/- 0.3V?
No
Measure voltage divider
at power tuning DAC, top
of R1121
No
Power tuning is low, else
R1121 around
replace U1125, else U1137,
2.45V +/- 0.15V?
U1138
Yes
Remove SH6 and measure
output pin 4 of U1130
Yes
U1130 pin 4
approximately
1.10 0.05V?
No
TP101
No
Transmitter PA overcurrent condition,
close to
else check U1101, R1103
1.5V?
Yes
Replace U1129, U1130
TX in Current control mode?
U1131, pin 4
TX is in current control mode, else PA is
saturated. Check SAT Reference tuning
per 12M to ensure tuning is not low.
No
Check U6101 or VOCON
signal DIG_CTRL_1049
Measure thermal cutback circuit
output at U1113, U1114 and U1121
Pin 4 of U1113,
Yes Replace log amp, U1105
U1114, and U1121 else U1112, else check
at 0V (logic low)? R1106 for 17 +/- 1 Ohm
No
Check temp. sensor
U1103, else U1148
U1127 pin 4
approximately
1.10 0.05V?
No
Replace U1127,
else U1126
Troubleshooting Charts: PA Failure
No
Replace U1132
is 5V?
Yes
Yes
Replace U1142