Motorola Astro XTL 1500 - Figure 5-32. no 16.8 Mhz Reference Oscillator Frequency (700-800 Mhz); No 16.8 Mhz Reference Oscillator Frequency (700-800 Mhz)

6815854H01-A June 15, 2005
Troubleshooting Charts: Flowcharts 5-43
5.6.32 No 16.8 MHz Reference Oscillator Frequency (700–800 MHz)
Figure 5-32. No 16.8 MHz Reference Oscillator Frequency (700–800 MHz)
MAEPF-27813-O
U6752
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 Y6750 for
16.8MHz
START
No 16.8MHz
Reference
No
Yes
>800mVpp
at TP6764?
No
Yes
Check
C6817
Replace
Y6750
3.0VDC
at pin 1 of
Y6750?
No
Yes
Check 3.0V
regulator path
from U6750
>500mVpp
at pin 2
U6752?
No
Yes
Check C6758
and R6756
>3.0Vpp
at pin 4
U6752?
No
Yes
Check
U6752
>1.4Vpp
at TP6762?
No
Check L6756,
C6755, C6759,
R6756 and C6760
Measure 16.8MHz Signals
with Oscilloscope having a
bandwidth >100MHz.
NOTE: L6756 and C6755 filter the
distorted output of U6752 resulting
in a clean sinusoidal 16.8MHz signal.
R6757 and C6759 adjust the amplitude.
Check Controller
Section and/or
ABACUS IC
U6000
Yes