No 16.8 Mhz Reference Oscillator Frequency (380-470 Mhz And 450-520 Mhz); Figure 5-15. No 16.8 Mhz Reference Oscillator Frequency (380-470 Mhz And 450-520 Mhz) - Motorola ASTRO XTL 1500 Detailed Service Manual

5-24
5.6.13 No 16.8 MHz Reference Oscillator Frequency (380–470 MHz and 450–520 MHz)
START
No 16.8MHz
Reference
Probe pin 3
of Y5750 for
16.8MHz
No
>800mVpp
16.8MHz?
Yes
No
>800mVpp
at pin 23
U5752?
Yes
>500mVpp
No
at pin 2
U5751?
Yes
>3.0Vpp
No
at pin 4
U5751?
Yes
No
>1.4Vpp
at TP5791?
Figure 5-15. No 16.8 MHz Reference Oscillator Frequency (380–470 MHz and 450–520 MHz)
June 15, 2005
Measure 16.8MHz Signals
with Oscilloscope having a
bandwidth >100MHz.
Check
C5761
Check C5760
and R5763
Check
U5751
Check L5753,
C5768, C5763,
R5768 and C5767
Troubleshooting Charts: Flowcharts
3.0VDC
No
at pin 4 of
Y5750?
Yes
Replace
Y5750
U5751 DC Voltages
Pin 1 No connection
Pin 2 1.5
Pin 3 Ground
Pin 4 1.5
Pin 5
NOTE: L5753 and C5768 filter the
distorted output of U5751 resulting
in a clean sinusoidal 16.8MHz signal.
R5768 and C5763 adjust the amplitude.
Check 3.0V
regulator path
from U5750
3
6815854H01-A