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

[Magnus Danielson]

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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