On Sun, 18 Sep 2005 15:52:03 -0500, James Meek <[EMAIL PROTECTED]>

>I've just found the time-nuts mail list, and the threads
>concerning the programming of the FEI FE-5680A rubidium
>frequency sources that some have bought on ebay and been
>unable to program.
>I, too, bought one of these from an internet source last year
>(a different source from the one mentioned in the thread I found),
>and was unable to get anything out of it by simply powering it
>up and connecting to it through its 10-pin interface using the
>pinouts for a standard FE-5680A.
>However, mine did not come naked or on a cut-off section of PC board
>like those I've seen advertised on ebay since then.  Rather, it
>came attached to a large board containing several voltage regulators,
>a serial interface buffer, a serial EPROM chip, and some other logic.
>Although I have not yet found the time to fully analyze the
>circuitry, it appears to have been set up so as to program the
>FE-5680A from the serial EPROM.  I have no idea whether it needs
>to receive a command from an external source to initiate that
>programming, or whether it happens at power-on (perhaps with the
>clocking of the serial EPROM by the FE-5680A itself?).
>I read that Rex and Brian Kirby have figured out that the unit needs
>a +5V supply (or perhaps just a logic input) in addition to
>the 15V supply in order to get any output.  If someone could
>provide me with specifics on that and anything else they've discovered
>about this part, I'd have a lot more incentive to try to figure
>out what the EPROM does -- and of course would share my findings
>with all here.

Here's what I worked out for the pins on the DB-9 on my5680A...

1   +15V  near 2A initially, dropping to about .8A warm
2   gnd
3   lock  high = unlock
4   +5V   about 160 mA
5   gnd
6   1 pps out
7   10 MHz out
8   RS-232 Rx  (into rubidium)
9   RS-232 Tx  (from rubidium)

The initial impression from the seller was that only 15V was needed. The
info on the FEI pages don't mention needing 5V in any option. A lot of
the pin functions are different from any description I have seen.

I think I have the same full board you have. I looked at it back around
the beginning of the year. If I remember right, the RS-232 pins of the
rubidium get fed from off-board signals. I did power it up using this
board once. There is a dual color led at the edge of the board that
indicates lock state, if I remember right.

Does your board have a sticker on it somewhere that says: SGLA4000B High
Stability Osc Assembly?  After lots if web searching, I figured that
this seems to be part of older Motorola Cell equipment. I found a site
that says they repair them. I tried sending an email asking if they have
any documentation, but got no reply.

Maybe later I can find time to scan the board. What I remember from the
hacking I did, was that there didn't seem to be anything intelligent
going on on the board. I don't remember any details though, maybe I
missed something.

Oh, on the side of the rubidium there is an adjustment screw. I thought
for sure this would adjust the C-field and hence the freq, but I don't
see any result by turning this. No idea what it is for.

I tried all sorts of things sent to the serial port but never saw any
effect or reply. I tried this at various baud rates. I also scoped the
other side of the MAX3232 chip inside, so I know the data was getting in
there.  The other port of the MAX3232 is connected too. It goes to what
must be a maintenance header inside. Nothing interesting came from
trying that port too.

So, if you feed it both 5V and 15V, I'd bet your unit will come up and
give you 1 pps and 10 MHz. If, like mine, the frequency is a little bit
off, it sure would be nice to know how to adjust it.

-Rex, KK6MK

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