Anritsu signal generator MG3642A - synthesizer unlocked.

[geshka]

Hello team.
I have Anritsu MG3642A which is showing that message on the screen "synthesizer unlocked"  .  It is not generating any output...  to be exact there is some output sometimes which off from the displayed frequency and it appears and disappears randomly.

Wondering if there any service manual or any idea of way to fix it (if any). 

Thanks
Gene.