[time-nuts] 5071A with ATTENTION flashing

Tom Van Baak tvb at LeapSecond.com
Wed Nov 9 17:28:45 EST 2016

Hi Li,

When there is a "fatal error" the unit goes back into standby mode, where the Cs oven is turned off. Hence the Cs oven temperature error will again be at its maximum value (which is that -9.55 number). This is by design.

I use a script to send a scpi syst:print? command once a minute, in additional to logging diagnostic information. That way you can see the unit slowly warm up and see how each of the readings stabilizes over time. What you may find is that the temp error starts at -9.55 and then slowly decreases to zero as the Cs oven warms up. If lock is not achieved the oven is turned off and the error slowly climbs back down to -9.55. This is by design.

Under ideal conditions a 5071A will lock within 10 to 15 minutes. But if the tube has been idle for months or years it can take half an hour or more. During this time the ion pump slowly improves the vacuum. So having a log file of periodic syst:print output allows you to follow the progress; of the ion pump, of the ovens, etc.

The fact that the log has only one entry suggests that someone cleared the entire log before you saw the instrument. That's unfortunate. It gives the impression the seller had something to hide.

Some comments on the diag information:

> Cs oven is up

This suggests there's nothing wrong with the ion pump or the cesium oven. Your oven heater and controller are fine.

> Low Cs beam signal = 3

This is consistent with a tube that's used up all its cesium.

> Raising emult voltage...
> Low Cs signal (37) with max Emult

This is consistent with a 5071 that's trying very hard to get enough beam signal, but there just isn't enough cesium left. If a high-performance tube, this is expected after 7 to 10 years of use.

> Fatal Error (see Log)

Unlike older cesium standards, the 5071A is quite clever. When there's nothing else to do, it does a clean shutdown of ovens and reports a fatal error. The unit goes into standby. When I refuse to give up I try powering up the unit again and again several times a day.

If I suspect the tube is the problem I swap tubes from a working 5071 frame. This is a very simple way to decide if the problem is the frame or the tube. After a couple of days of trying, and if the diag messages and fatal errors are consistent, then I finally admit defeat and mark the tube bad. The good news is you then have an entire frame of spare parts! And also a Cs tube to put on the "Dremel" pile!

Finally, remember that even in standby mode, a 5071A makes a very attractive, high-quality 10 MHz quartz standard, with multiple output frequencies, with high-resolution digital frequency tuning, a LED clock and 1PPS input/output. You can turn it into a GPSDO by sending phase or frequency step SCPI commands. That is, there's no need for a DAC or EFC; we've talked before on the list about the advantages of a DDS-based GPSDO instead of the traditional DAC/EFC method.


----- Original Message ----- 
From: Li Ang 
To: Tom Van Baak ; Discussion of precise time and frequency measurement 
Sent: Tuesday, November 08, 2016 10:48 PM
Subject: Re: [time-nuts] 5071A with ATTENTION flashing

Hi Tom

I have collected the log from it. Log level is service. The 9.2G pll pass the test today. The log during the power-up process is also included.


Li Ang / BI7LNQ


scpi >

MJD        0 02:02:18

CBT ID: 3128A00642(H)

Status summary: Fatal Error (see Log)

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