Dear Ann Landers,
I have had a curious situation while testing a (HP) 3325A with opt 001 (high stab TB) I noticed the Ref frequency had drifted up 150 hz and I could only bring it down to 73 hz above 10 MHz. I thought well it's one of 2 and they are getting old so I may as well get them out of my pool of equipment. Well #2 is measuring about 200 Hz high and I doubt it will adjust down either. I had optimized it July 2007.
These are oldies with serial # starting with 17 (1977?). Anyone know of an "event" that could have brought this about? I can't say they were plugged in 24/7 but maybe they just hit the end of thier life. I suppose I should be thankful they still work at all.
Either way I can just unplug the optional assy and call them standard models and they perform within those parameters.
Just curious if anyone can give me some insight here.
Signed,
Curious in Texas
Opt 001 on the A and B are both 5 ppm same as the standard.
If you are a gidep user check 33k3-4-2587-1 and 33k3-4-192-1'
(it could be 10 ppm not sure off hand but the tolerances are the same for opt 001.) I think its +/- 100 Hz at 20 MHz.
It sounds like you may not have the rear panel jumper installed between the Oven Output and the Reference Input. That would definitely cause the symptoms that you describe.
The ovens go bad in these old timebases. Offhand I would have said that would make the frequency go low, but I can't recall for certain. I have heard of people repairing them but I think the oven you have is pretty ubiquitous. If you want to pm me the part number on your oscillator I will check and see if I have any laying around.
Quote from: Duckbutta on 01-07-2009 -- 09:11:20
It sounds like you may not have the rear panel jumper installed between the Oven Output and the Reference Input. That would definitely cause the symptoms that you describe.
That would definitly cause the problem.
Well as they say, S--t happens.
Jumper was installed and measured bad. Same result when measuring oven ref output on rear panel.
Thanks for the thoughts.
Adjusting both the Coarse and Fine adjustments wouldn't bring it in? Is there any ripple on the output?
That was all the coarse would do for me, the fine didn't have any significant effect since I couldn't close enough to nominal. I just disconnected then and went with the standard freg ref.
Not worth spending additional effort on them.
I have repaired a few of these - many of them have 109 deg C thermal fuses to the ovens. Once this fuse blows, there is no oven to keep the crystal stable and it drifts to no end. Before removing it, take a heat gun and warm up the case. If it drifts past 10 MHz to the opposite side of where you were trying to adjust from, it is this thermal fuse (same fuse found in a lot of hair dryers that causes them to stop working when they get clogged).
Note to Navy calibrators: there is a serious defect in the NAVAIR procedures in this area. The Navy only checks the timebase is within the total drift tolerance since the last calibration (3 year interval!) and does NOT attempt to align it back. With a defective fuse on the oven, a bad oscillator could easily get past calibration if the whole unit managed to warm it up enough. A retuning to optimum, as a part of the standard process, will reveal the blown fuse (no oven) since it will drift too much to get tuned in. I mentioned this to the Navy auditors but they did not seem to care.