Motorola Astro XTL 1500 - Figure 5-15. no 16.8 Mhz Reference Oscillator Frequency (380-470 Mhz and 450-520 Mhz); No 16.8 Mhz Reference Oscillator Frequency (380-470 Mhz and 450-520 Mhz)

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