[time-nuts] Re: FE-5680A Adjustment board

[Bob Camp]

Hi

One of the most basic issues here (and this is only a guess):

I don’t think there is one “current version” of this part. 

First off, They customize these for the needs of various OEM’s. One outfit wants this another outfit wants that. Some of these mods are obvious (no SMA RF output connector). Others are not so obvious. They do not all show up in some sort of decodable part number. 

Next up, They obviously change the design from time to time. These parts have been around for quite a while. Components go out of stock. The folks  have to do something to keep the line going. They also have streamlined the assembly process more than a bit over the years.

Some companies would spin up a range of part numbers and revisions for all of this. Just how valuable that is vs tracking serial number ranges … who knows. The OEM is probably fine with either approach. 

Finally: What we see on eBay may be from “who knows when”. Systems get scrapped out for a range of reasons. Parts get hoarded and re-sold for years after a scrap out. What somebody got 6 years ago may well be newer than what I buy today. Date codes might help with this. It’s also possible that some OEM’s asked them to “freeze” the design (so new parts are done the old way …).  

Fun !!!

Bob

> On Nov 24, 2025, at 6:11 PM, Magnus Danielson via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Hi Luca,
> 
> First of all, what a big effort! You seem to really been able to come far on this!
> 
> Serial commands and schematics are for sure of interest, but indeed all.
> 
> Since there are so many versions, it would be interesting to see if a few others could be covered so that more people get relevant help.
> The history of this model have been a bit messy, so if we could start to gather a little more on it to have more comprehensable info, I think that would be welcome.
> 
> I have at least one of these around here somewhere, unknown which exact version at this point.
> 
> Enjoyed you toyed with some modifications and documenting them. I think I recall others doing various forms of modifications, even if most seemed to set the output frequency to meet the needs of particular uses such as CD-players back in the day. As I recall others could not.
> 
> Are you aware of the little book "Rubidium Frequency Standards Primer" by W.J.Riley? You might find that both a nice read and quite relevant. I came to think of it when I saw the schematics, as it includes some examples too, and good reasonings around it.
> 
> Cheers,
> Magnus
> 
> Den 2025-11-21 kl. 10:58, skrev Luca Pandolfini via time-nuts:
>> Hello,
>> This is my first post. :)
>> I found many old posts about the topic but to my knowledge none seems to
>> include this content, AFAIK.
>> I happen to have almost completed the majority of the reverse engineering
>> of the Temperature-controlled voltage "Adjustment Board" of an (old?)
>> FE-5680A (Since there are many different version, I am talking about the
>> exact model shown in this page:
>> http://www.dd1us.de/Downloads/precise%20reference%20frequency%20rev%201_1.pdf
>> ).
>> 
>> If anybody is interested, I can share one or more of the following items:
>> - "pseudo-schematics" of the board,
>> - decompiled and (mostly) annotated microcontroller code
>> - description of the (full set? of) serial commands
>> - memory and EEPROM maps
>> - Temperature/Voltage calibration values
>> 
>> I started the project as a fun way to refresh my 8051 assembly skills and
>> play with useful tools while doing so (e.g. dumping the SPI EEPROM with a
>> BusPirate, dumping the PSD ROM with an Arduino, learning to use Ghidra,
>> etc...).
>> Since it might take quite a bit of time I just wanted to have feedback from
>> the community and know if it might be worth tidying up this material (but
>> only if there is some interest, since it looks like a device becoming
>> obsolete...).
>> Please let me know what you think and greetings to everybody!
>> 
>> LucaPandolfini
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