No 16.8 Mhz Reference Oscillator Frequency (700-800 Mhz); Figure 5-34. No 16.8 Mhz Reference Oscillator Frequency (700-800 Mhz) - Motorola ASTRO Digital XTL 5000 Detailed Service Manual

5-46
5.6.32 No 16.8 MHz Reference Oscillator Frequency (700–800 MHz)
START
No 16.8MHz
Reference
Probe pin 3
of Y6750 for
16.8MHz
No
>800mVpp
16.8MHz?
Yes
>800mVpp
at TP6764?
Yes
>500mVpp
at pin 2
U6752?
Yes
>3.0Vpp
at pin 4
U6752?
Yes
>1.4Vpp
at TP6762?
Yes
Check Controller
Section and/or
ABACUS IC
U6000
Figure 5-34. No 16.8 MHz Reference Oscillator Frequency (700–800 MHz)
May 25, 2005
Measure 16.8MHz Signals
with Oscilloscope having a
bandwidth >100MHz.
No
Check
C6817
No
Check C6758
and R6756
No
Check
U6752
Check L6756,
No
C6755, C6759,
R6756 and C6760
Troubleshooting Charts: Flowcharts
3.0VDC
No
at pin 1 of
Y6750?
Yes
Replace
Y6750
DC Voltages
U6752
Pin 1 No connection
Pin 2 1.5
Pin 3 Ground
Pin 4 1.5
Pin 5 3
NOTE: L6756 and C6755 filter the
distorted output of U6752 resulting
in a clean sinusoidal 16.8MHz signal.
R6757 and C6759 adjust the amplitude.
MAEPF-27813-O
Check 3.0V
regulator path
from U6750
6881096C74-B