Electronics > Repair
Help needed for repair of Efratom FRS-C rubidium oscillator
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edpalmer42:
Sorry for the late response.  Life intervened.


--- Quote from: ejd.pol on June 07, 2024, 08:31:45 am ---Hi Ed, Just to give you an update on the state of things:

-As far as I can tell, the fan is connected to the proper connector as indicated on the main PCB. As remarked earlier, it may be that the Rb oscillator is fine without it in stand-by.
 The oscillator is bolted to quite a large heat sink, being the floor plate of thick solid aluminum that runs completely front-to-back, and had good thermal contact
 with the external metal box. So, if the power consumption of the counter itself is low enough in stand-by, the oscillator may be cool enough.
 When the counter is switched on, the fan will help thermal flow to the external box.
 This also provides motivation why the fan is allowed to run on a supply that is different from the Rb oscillator supply....

--- End quote ---

I finally found the reference to the fan that had me confused.  My PM6681 has a fan.  If you add the Rb option, that's fine since there's already a fan present.  But in your PM6685, the basic unit has no fan so the comment regarding the fan header for the Rb option makes perfect sense.  I thought it referred to a different fan header for the Rb option but it just meant that only the Rb option has a fan.   :palm:

In any case, if you have a temperature probe, it would be a good idea to measure the temperature of the Rb after it's been running for a week or so and see how it's doing.


--- Quote ----Speaking about thermals, I have disassembled the new supply in order to drill some holes in the three enclosures. It should not be urgent or even necessary,
 but I thought it would help to reduce temp inside the three boxes as much as possible. The metal supply protection box doubles as a heat sink as well.

--- End quote ---

Sounds good.  Without knowing the efficiency of those supplies, it's hard to know how warm they will get.  More ventilation can't hurt.


--- Quote ----Doing precise measurements: I would hope (have not investigated this point yet) that, in stead of making 10 measurements of 100 seconds each,
 it is possible to set up a measurement of 1000 seconds. When doing so, the statistics of the results would improve, I think. Or am I missing something?

--- End quote ---

Good question.  And I don't really have a good answer.  But I suspect that it depends on exactly what you're trying to measure.  I think that an average of ten measurements of 100 sec. each would be equivalent to a single measurement of 1000 sec. but the single measurement might hide glitches that multiple measurements might make visible.  If I'm suspicious that a nominally stable oscillator might be jumpy, I occasionally check the standard deviation of the measurements to check for stability.  That wouldn't be possible with a single measurement.


--- Quote ---Anyway, it has been a great experience doing this repair, and I would like to thank you for all your help and guidance!

--- End quote ---

That's what we're here for!   :-+
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