[time-nuts] Adjusting nominal frequency of FTS 1200-100 OCXO?

[Magnus Danielson]

Dave,

While this is a bit of a tangent out of normal time-nuts, it still has 
some relevance in terms handling of old equipment. Lets not get to crazy 
on this tangent.

We had a similar issue many years ago. The BGA mounted chips would break 
away from the boards and rattle around after transport. Quite annoying 
for new gear.

The investigation took quite some time, but in the end, it turned out 
that the gold layer had got too tick, and as you solder gold, it 
dissolves into the solder, and if you now have too high ratio of gold, 
you get brittle layers of gold-tin alloy which is much more fragile than 
a solder joint is. As the PCB fab got their gold layer thickness in 
control, the problem went away.

One method used in hand-soldering of gold-layered boards is to solder 
it, then clean it right off and then solder again. This way most of the 
gold gets removed and a clean contact achieved.

Gold does have benefits for the connector parts among other things.

Cheers,
Magnus

On 09/20/2016 12:24 AM, Dave M wrote:
> Adrian,
> Your connector has probably experienced a problem common to gold plated
> contacts and component leads.  Years ago, I worked in the avionics
> repair and calibration facility at the Navy base in Jacksonville, FL.  I
> saw this quite frequently in HP and Tektronix instruments that had been
> in service for a number of years.
> The issue is that the gold plating peels away from the base metal of the
> contact or component lead, exposing the base metal to contaminants. Our
> microminiature soldering lab began instructing all technicians to
> completely remove the affected components and tin the leads with
> solder.  Then, wick away the solder to completely rid the amalgam of the
> gold, then resolder the component in place.
> This was the only permanent solution to the problem; it might occur on a
> different component, but not on the one that was properly repaired.
>
> More often than not, the problem was exhibited as an intermittent
> failure, consistant with board flexure or pressure.  Some of the
> problems were very hard to find, but we had to keep investigating until
> we had isolated the real point of failure.
>
> Cheers,
> Dave M
>
>
> Adrian wrote:
>>> Christopher,
>>>
>>> my 4060 has been locking exactly 0.5 Hz off of the correct frequency.
>>> The 1000B has had a contact problem on the edge connector.
>>> Over the years, an insulating black layer had built up between the
>>> solder and the gold plating of the contacts.
>>> I had to re-solder each of them carefully twice to get it working
>>> reliably.
>>>
>>> Regards,
>>> Adrian
>>>
>>> Christopher Hoover schrieb:
>>>> I've been debugging a FTS 4050 with the 5000M module.
>>>>
>>>> It looks like the problem is the FTS 1200-100 OCXO.   It seems to
>>>> have aged to the point that it is very low in frequency.   (Chuck
>>>> Harris reported a similar situation a long time ago.)
>>>>
>>>> I have it out of the 5000M and determined that I need to give it
>>>> +8.8V on the control to get it within 50uHz of 5 MHz.
>>>>
>>>> The power draw after a short warm up is < 2.5W (on this hot day);
>>>> it looks like the oven is behaving.
>>>>
>>>> Has anyone figured out how  to adjust the nominal frequency of an
>>>> FTS 1200 -100 to recover the EFC range?
>>>>
>>>> Also, anyone have a schematic for any model of the FTS 1200?
>>>>
>>>> Thanks,
>>>> -christopher
>>>> 73 de AI6KG
>
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