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

[Palfreyman, Jim L]

Thanks folks for all your efforts.

It turns out I was right about the 10811. My replacement 10811 fixed the fault but as Chuck pointed out I was being to much of a cowboy with the course adjustment. Instead I tuned the course control of the 10811 to a reference 5 MHz on the bench and then plugged it all in. This time it worked and it stayed working well too! I've been calibrating the C field over the last 12 hours.

Now of course I'm turning my attention to the 10811. I would like to fix that!

With the heater off, the oscillator behaves well with the course adjustment providing the appropriate control (haven't check the EFC yet at this temperature). It is of course below 10 MHz. When the heater is powered it does the right thing (0.5 amp for a few minutes then drops back). The frequency rises to a bit over 10.0000 MHz. However the course control no longer has any effect whatsoever.

I'm guessing there are some components in the oscillator circuit that are heat damaged after two and a half decades of being in an 82 degree oven. I'm going to follow through the manual and see what I can find.

However, if anyone has experienced this pattern before - please let me know.

Thanks again for all your help!

Regards,


Jim Palfreyman


-----Original Message-----
From: service at frequencystandards.com [mailto:service at frequencystandards.com]
Sent: Friday, 9 May 2008 4:00 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] HP/Agilent 5065A Rubidium Vapour frequency standard problem

You didn't really say in your description but you really need to have the loop open using the front panel switch before you try to adjust the oscillator. Unless you are very familiar with how tiny of a turn it takes to make it too far off to lock, you will have it out of range very quickly. Open the loop and connect the 5Mhz output to a good frequency counter, preferably one that is synched to another rubidium, GPS locked crystal or cesium. Once connected, adjust your crystal coarse adjust for as close to 5Mhz as possible. If you can't get it below a 0.1 hz error, you are going to have trouble getting the unit to lock. Make sure you allow a good warm up time for the crystal in the 5065 before you do any adjusting.
If you can get the crystal to that small of an error, then close your loop and watch the control meter setting. Typical is that the meter will move a small amount but not peg. If it pegs, you have another problem with the unit. If it moves a small amount and stops, you can then adjust the coarse or fine and bring the meter back to zero. If you use the coarse adjust, at this point, you are going to be making VERY tiny adjustments of it.
Let us know what you find from this and we can move you to the next step.
Chuck Norton