Motorola APX 7000 Detailed Service Manual page 142

5-38
RX RF Failure – Page 6
6
Check LNA:
Check DC bias voltages for U406 at
the base (pin 1) & collector (pin 3).
Is base voltage =
0.778 V? and
collector voltage =
1.554 V?
Yes
Check DC bias voltages of Q402 at
the base (pin 2 or 5) , collector (pin
6) & emitter (pin 1).
Is base voltage = 1.024
V? Collector voltage =
0.777 V? Emitter
voltage = 1.554 V?
Yes
Check DC input line voltages
and visually inspect and
replace defective
components if needed.
Note: RF Test frequency used:
VHF: 154.275 MHz
UHF1: 424.975 MHz
UHF2: 485.075 MHz
700: 769.0625 MHz
800: 860.0625 MHz
Measured with a high impedance probe for relative comparisons
and troubleshooting only. Actual S21 gain or loss may differ if
the test point is not 50 ohms.
No
Replace
U406
No
Replace
Q402
Troubleshooting Charts: RX RF Failure
7
Check LNA:
Check DC bias voltages for U407 at
the base (pin 1) & collector (pin 3).
Is base voltage =
0.778 V? and
collector voltage =
1.552 V?
Yes
Check DC bias voltages of Q403 at
the base (pin 2 or 5), collector (pin
3) & emitter (pin 4).
Is base voltage = 1.025
V? Collector voltage =
0.778 V? Emitter voltage
= 1.552 V?
Yes
Check DC input line voltages
and visually inspect and
replace defective
components if needed.
No
Replace
U407
No
Replace
Q403