Motorola APX 5000 Service Manual page 148

5-42
RX RF Failure – Page 8
Clock
9
Synthesizer
Measure tuning
voltage (Vt) at
R608
No
CLK_SSI_RX
< 1.2 MHz?
Yes
No
Vt = 3 Vdc?
Yes
Repair
Defects
Note: RF Test frequency used:
VHF: 154.275MHz
UHF1: 424.975MHz
UHF2: 485.075 MHz
700: 769.0625MHz
800: 860.0625MHz
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.
Vt = 0 Vdc?
Yes
10
Remove SH6A, inspect
clock oscillator circuit
at U601-19,20
Visual
No
examination
OK?
Yes
Replace Varactor
VR601
No
10
Check level shifters, U603 and U604 by
checking signal amplitudes using an
oscilloscope at R616, R617, R618. R616
and R617 belong to U603 and R618 belongs
to U604. Note: These resistors are not
placed. You will be probing the pads.
Troubleshooting Charts: RX RF Failure
10
Remove SH6A,
inspect
components
Visual
No
examination
OK?
Yes
Is the input side
No
pad of R616, R617
& R618 = 3 V?
Yes
Is the output side
No
pad of R616, R617
& R618 = 1.875 V?
Yes
Replace
Abacus,
U601
Repair
defects
Replace
Abacus,
U601
Replace level
shifters, either
U603, U604 or both.