Motorola APX 3000 Detailed Service Manual page 124

5-34
RX RF Failure – Page 8
Clock
Synthesizer
9
Measure tuning
voltage (Vt) at
R608
No
CLK_SSI_RX
< 1.2 MHz?
Yes
No
Vt = 3 Vdc?
10
Yes
No
Repair
Defects
No
10
Vt = 0 Vdc?
Yes
Remove SH11 , inspect
clock oscillator circuit at
U601-19,20
Visual
examination
Yes
Replace Varactor
VR601
Note: RF Test frequency used:
UHF1: 424.975MHz
UHF2: 485.075MHz
10
VHF: 154.275MHz
700:
800:
Measured with a High Frequency Probe for relative comparisons and troubleshooting
Remove SH11,
only. Actual S21 gain or loss may differ if the test point is not 50 ohms.
inspect
components
Visual
No
examination
OK?
Yes
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.
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
Troubleshooting Charts: RX RF Failure
769.0625MHz
860.0625MHz
Repair
defects
Replace
Abacus,
U601
Replace level
shifters, either
U603, U604 or
both.