Motorola APX 1000 Detailed Service Manual page 137

Troubleshooting Charts: RX RF Failure
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?
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?
Check DC input line voltages
and visually inspect and
replace defective
components if needed.
Note: RF Test frequency used:
VHF: 154.275MHz
UHF1: 424.975MHz
UHF2: 485.075MHz
700: 769.0625MHz
800: 860.0625MHz
900: 938.0625MHz
Measured with a High Frequency 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
Yes
No
Replace
Q402
Yes
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.
5-39
No
Replace
U407
No
Replace
Q403