[time-nuts] Fwd: FE-5680A Physics package

Peter Bell bell.peter at gmail.com
Sat Oct 29 16:54:00 UTC 2011

I was wondering if anyone on the list has ever had a play with these
things?  I had a couple of dead ones, and have managed to get the
first one working (easy fix - the 3.3V regulator was dead), but the
second seems to be a lot more troublesome.

Basically, everything seems to be working, but there is no resonance
dip detected at the photocell - however all the individual parts seem
to be OK.  I did a couple of quick and dirty tests firstly by swapping
the entire Rb cell assembly over between the two units - and the fault
swapped over with the Rb cell.  Both cells are running at the same
temperature, the photcells are good, and the working one still works
(on both main boards) even when you swap the snap diode / filter
assembly or the shield / c-field coil from the bad one.

Basically, all that's left is the photocell (which seems to pick up
light OK), the FET / Thermistor (unlikely, since the heater works
correctly), the lens (looks perfect) and the Rb cell itself.  So I'm
tending towards the "bad Rb cell" idea - but the problem is that I've
fixed quite a few Rb oscillators in the past (mostly Efratom FRKs and
a few FRSes) and I've never seen a bad Rb cell.  So I was wondering if
anyone else on this list thought it seemed likely.

(resent with the photo reduced in size).

Incidentally, when I was looking at the Rb cell, I noticed that it
seemed to be a pair of cells held together in a heat-shrink tube - I
assume that the first (slightly smaller) one is a isotopic filter and
the second is the actual absorption cell?

And does anyone have any schematics for these things?  FEI seem to
have the standard "send it back to us" approach that is increasingly
common recently - another reason I liked the FRSes.
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