Motorola APX 3000 Detailed Service Manual page 144

5-54
PA Failure – Page 4(ALC)
Remove SH15 and measure
PA control voltage at
U1601 for UHF1 and
U1001 for 7800MH
pin 4
VC_OFFSET low,
remove SH6
U1133 pin6
about 5V?
U1133 pin 3
4.1V +/- 0.6V?
R1180 close to 5V?
Remove SH3 and
measure U1142 pin4
U1142 pin4
1.00V +/- 0.3V?
Measure voltage divider
at power tuning DAC, top
of R1121
R1121 around
2.45V +/- 0.15V?
Remove SH6 and measure
output pin 4 of U1130
U1130 pin 4
approximately
1.10 0.05V?
Replace U1129, U1130
4
Yes
No
PA_OFFSET low,
Yes
check U1125 pin 1
for approx. 1V, else
replace U1133
No
No
Measure TP6107
Yes
No
TP6107 1.8V?
Yes
Replace U1139 or
associated logic
Yes
No
No
Power tuning is low, else
replace U1125, else U1137,
U1138
Yes
Yes
No
TP101
No
Transmitter PA overcurrent condition,
close to
else check U1101, R1103
1.5V?
Yes
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.
Check U6101 or VOCON
signal DIG_CTRL_1049
Measure thermal cutback circuit
output at U1113, U1114 and U1121
Pin 4 of U1113, Replace log amp, U1105
Yes
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