Motorola APX 2000 - Page 162

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