From what I see and understand :
A18 YTO oscilator, A21 LO distribution oscilator and A20 Lowband board seems to be OK.
Problem seems to be more on A13 Front end driver board or A12 LO Synthesizer board.
Can you help me on this repair ?

From what i read in the service manual the error message I have ("1St LO unlock, failure acquiring FracN frequency lock") refer more to the A12 board.


Here is what I plan to do:
1-Verify the sampler out signal, should be 0dBm at 4Ghz at the power on of the unit.
2-Verify the 600 MHz signal from the motherboard. It should be at about -5 dBm
3-Verify the 10MHz signal , it should be at 2 dBm