Electronics > Repair
E4433B RF sig gen repair
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microbug:
It now reports error 508, frac-N loop unlocked.

This definitely wasn't there before -- the only error was oven cold. UNLEVEL was displayed but no error was present. I have seen someone online mention that the frac-N error can be intermittent, but it's also possible I've caused it. It goes away if cleared when the out-of-lock LED is off, so I think the error reporting is working.

I checked the supply rails on the synth board (had to solder wires to testpoints and re-attach the board), and the 10MHz reference output on the back of the unit. All were fine.

Edit: the frac-N error has now disappeared again. It is quite likely that it appeared and disappeared before and I didn't notice -- after I first checked the error queue and found only oven cold, I didn't check it very often again.
vaualbus:
Oh I see! Anyway the interesting thing is that the Frac-N locks the signal before the doubling and filtering stage, I rather would check, as you said, that part.
So If something is wrong on that path it would never unlock the PLL. Maybe also having the board case removed cause more unlocking due to  the board not been shielded?
microbug:
Yes, it could be that the board being unshielded is causing the PLL to unlock. I will put the shield back on and do a frequency sweep. If I don't get the unlock error then I think I could ignore it for now.
vaualbus:
Any new regarding the repair? I am curious  if you found something bad on the filtering  and doubling section! ;)
microbug:
I’ve been quite busy this week. Don’t worry, I’ll have a look at the weekend!
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