User's Manual

26
8.5 Frequency Synthesizer Trouble
Start
↓
Perform visual inspection on the VCO of the PLL
and devices around the PLL IC (U401).
Are they normal?
Yes
→
Clean the faulty parts and recover them.
No↓
Check the CPU ports (P1.4, P1.5, and P6.0).
Are the data from Pin No. 11 (clock), Pin No. 13
(Data), and Pin No. 14 (Enable) of U401
normal? (Scope)
No
→
Yes↓
Check 12.8MHz TCXO and the power
supply part of U402, and replace them
if necessary.
Does Pin No. 1 of U401 oscillate 12.8MHz?
(Spectrum)
No
→
Yes↓
Check the power lines of U401 and U402.
Are voltages at Pins No. 4 and No. 5 of U401
normal (5V)? (VTVM)
No
→
Yes↓
Check resistances and voltages of the VR11,
the R105, the R106, and the R107.
Is it possible to create oscillation frequency of
the TCXO using the VR11?
No
→
Yes↓
Trouble in other parts