[time-nuts] Tuning a Symmetricom 1111C

Tom Knox actast at hotmail.com
Sat Jul 8 15:18:17 EDT 2017

Hi Ed;

Thanks for the response. Great logic/detail on potential issues and solutions. The power supply issue seems completely intermittent and when running may be completely fine. That said I am leaning toward the power supply being the issue, it would explain all the issues. I first saw the power supply issue with the batteries installed, I removed the fuse and the missing voltages came up and the unit locked. before with those voltages absent it was displaying the lock light every few seconds after warmup. I had assumed a bad battery had created too great a load on the supply. But it failed to come up again when I rebooted and then came up again the next time I rebooted. It is either zero or correct. I have several problematic 4065's and thought they had 1000B's, I will check if any have a 1111C. It would be easy to swap them and would resolve the question of if these problems are related. The unit I have may actually be locking but outside it's acceptable EFC range. Phase Noise is exceptional about -120dB @ 1Hz offset 5MHz.

I will look at solder on the bricks, for the symptoms that could be the issue.

Thanks again for your help;

Thomas Knox

From: time-nuts <time-nuts-bounces at febo.com> on behalf of Ed Palmer <ed_palmer at sasktel.net>
Sent: Saturday, July 8, 2017 12:03 PM
To: time-nuts at febo.com
Subject: Re: [time-nuts] Tuning a Symmetricom 1111C

Hi Tom,

I have a Datum 4065A standard with a Datum 1111B oscillator.  I've never
had to tune it, but it appears to be a clone of the HP 10811 so you
might get some insights by researching that oscillator. However, if
you're having issues with the +-15V supplies, I'd STRONGLY suggest that
you resolve those before attempting to retune the oscillator.

Circuit information for these units isn't available, but reading between
the lines, I note the following:
- My unit uses an AD9713BAP D/A converter to drive the EFC.  It requires
+-5V supplies.
- The system monitors +5V, +15V, and -15V, but not -5V so where is -5V
coming from?  I see an LM320-5V on the mainboard near the D/A converter.

My first guess is that -5V is derived from the -15V supply.  If that's
true, flaky +-15V supplies will almost guarantee a flaky EFC.  Since
your unit was able to lock once, it further suggests that retuning isn't

There's a power supply board bolted to one of the side panels that uses
a couple of DC-DC bricks.  I found some bad solder joints on that
board.  I can't remember the details.  You might want to check that out.

Since these units are microprocessor controlled and include multiple
tests and measurements to ensure that the lock is on the correct signal
peak I don't think it's going to lock to the wrong peak.

You should also be aware that these units use a STEL-1173 chip to drive
the D/A converter.  This chip is infamous for failing after a few
years.  If you search the archives you'll find more info on that topic.
I found a source for this chip a few years ago, but it looks like that
source has dried up.


On 2017-07-08 10:00 AM, Tom Knox <actast at hotmail.com> wrote:
> Hi All;
> Does anyone have a data sheet or experience with the Symmetricom 1111C, I have one in a Symmetricom 4065C and the internal diagnostics say it is at the end of it's tuning range. Is there a way to do a coarse manual adjustment, or is it a possibility the Cesium is locking to a side peak? In addition the +- 15 volt supplies have failed to switch on twice during testing, but have switch on after rebooting. On one reboot it locked quickly.
> Thanks;
> Thomas Knox

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