[time-nuts] HP/Agilent 5065A Rubidium Vapour frequency standard problem

Palfreyman, Jim L Jim.Palfreyman at team.telstra.com
Thu May 8 00:21:12 EDT 2008

Hi all,

I'm in need of someone with some experience in fault finding a 5065A. I'm having a go at repairing my university's old unit which up until a short while ago was working well. I've got the PDF of the manual and I've been testing and trying various things but I need someone with a bit of experience with these units to help diagnose the fault.


A) The unit drifts at about 1 usec/sec.

B)  The CONTROL reading is pegged off the scale.

C) The course oscillator adjustment doesn't affect the CONTROL reading.

D) A8TP3 doesn't seem to produce anything but a straight line, however A8TP2 is fine.

The fact that the course oscillator didn't seem to do anything made me suspect the 10811-60109 OCXO. I happen to have a spare 10811-60111 and so I powered off the unit, substituted the (cold) 10811-60111 and powered on. The course oscillator control could adjust the CONTROL reading and within a minute or two the unit was drifting at only 80 picosec/sec.

Voila - problem solved!

However, 8 hours later the CONTROL level was pegging the meter again and the unit was drifting at 1 usec/sec.

And now the oscillator course control had no effect on the CONTROL level.

So why is that a luke warm 10811 combined with a hot RVFR allowed the unit to function, but once the 10811 heated up it drifted again?

The Continuous Operation light operates all the time and the Integrator Limit light comes on after a while as expected when the CONTROL voltage is high.

Any hints or tips will be appreciated.

Jim Palfreyman

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