Hey guys!
I'm having problems with my 4421B, it simply doesn't activate the modulation, I hear the sound from the relay, but it doesn't work. It's like trying to activate modulation, but it doesn't, I've already done some tests:
1) I used the external modulation input and it worked well;
2) The OCXO is in order, 10mhz perfect and signal without imperfections.
One detail, about a year ago, my time base stopped working and I replaced it with the same one (ebay) and everything went back to normal, I don't have the service manual, if someone could make it available it would be of great help.
Note: The signal in blue and the attempt to modulate in FM (dev=100khz)
Hug!
imaurente .
