[time-nuts] Testing the Datum LPRO Rb oscillator

Bob Camp kb8tq at n1k.org
Wed Jun 17 18:24:02 EDT 2015


Some quick hints:

1) The “lifespan” number is very approximate. There is a slow drop off in the bulb. It may or
may not get you on a modern Rb.

2) Heat is the real killer on these gizmos. Run one without a heatsink and it will last a few years.
Run it with cooling that keeps it’s internals below 45C and it will last much longer. 

3) The lamp monitor output is one way to see what’s going on. They started out with a design
that gave about 6V when new. Later units have a circuit that starts out around 9V. In both cases
the trick is to check it when new and watch for it to drop. 

4) There are ways to “revive” certain forms of dead bulbs. A lot depends on exactly why your
bulb died (if it’s the problem). 

5) Things like RF transistors and tantalum bypass capacitors die in these units just like they 
do in anything else. They can be replaced and things will work. 

7) VCXO drift is one way Rb’s die. It’s more of an issue on the FEI’s that the LPRO’s. In that 
case tweaking the VCXO trimmer cap to re-center things fixes a unit that simply stays
in search mode. 

There are lots more tricks. ….


> On Jun 17, 2015, at 3:08 PM, Sean Gallagher <sean at wetstonetech.com> wrote:
> Good afternoon everyone,
> So I have a bunch of Datum and Efratom LPRO Rb oscillators. I know that one of them is bad and I already swapped it out. I was getting really long lock times (if lock at all happened) and read that was an indicator.
> These things were all made from like 1999-2001 or so and from what I understand have about a 15 year lifespan. However a former colleague told me today that this limitation is really only if they are powered on. Is this true? If so then some of these units apparently were only hooked up for a couple years and then the servers they were in were taken offline and they may still have 10+ years of service right?
> I was really wondering if someone could point me in the right direction (or towards a tutorial) on how I can test these and see if they are still okay? I don't have a lot of engineering experience but I do have access to a multi-meter and an oscilloscope and a decent amount of luck when it comes to troubleshooting.
> Respectfully,
> Sean Gallagher
> Malware Analyst
> 571-340-3475
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