[time-nuts] Z3816 Oscillator Saga

GandalfG8 at aol.com GandalfG8 at aol.com
Fri May 2 13:08:33 UTC 2014

Hi Chris
I've got some results to hand for three samples of the fluke.l  
MTI-260-0624-C oscillator, if that's the one you mean?, and for 5 MHz  output they all 
require an EFC input on pin 1 between  2.8 and 3.1 Volts.
That's with a 12 Volt supply on pin 5, which gives approx 6 Volts out on  
the Ref Volt Out pin, pin 2.
So it would seem, in this respect at least, that they are quite close to  
your original oscillator, although I don't see any figures for EFC  
sensitivity in those particular results, but I wonder if there's any  possibility of 
an initial adjustment in the Z3816, either hardware or  software, that might 
limit the EFC range to more closely match individual  oscillators?
In a message dated 02/05/2014 13:31:41 GMT Daylight Time,  
syseng.greenfield at btconnect.com writes:

On  05/01/14 08:51, Peter Schmelcher wrote:
> Chris,
> This hi res pic  might help you. I modified my Z3816A to improve the
> performance. I  changed the grounding and added a few extra capacitors.
> This pic is  close to the start so very few changes.
>  -Peter


Thanks very much for sending that. The damage is  in fact to the underside
of the board, not the top side. I was using a  solder sucker to remove the
solder around each oscillator pin, which was  then free enough of solder
to use pliers to wiggle each lead side to side  to free up. Unfortunately,
the pliers slipped and sheared off ~3 parts from  the underside of the 
It's not clear if all the parts are  resistors or caps, though one is a cap
for sure. It's too much to expect  you to strip your board out just to send 
pic, but if you ever have to do  that, a jpg would be appreciated. It's 
difficult to find info on  these units, and haven't been able to find a 
It's not clear  what all the pins of the header are for, though some may 
be to  flash
the cpu with firmware. There may also be added factory commands for  
things like
replacing the oscillator, though one would expect that to  be an auto 
within the firmware. The fact that the efc always  returns to the most 
recent value
at power up and not do a sweep through  the whole range might suggest 
this is not
the case.

Anyway,  powered up the original 260-0558 oscillator on the bench today, 
a  helipot of the efc input and get the following:

EFC     Frequency, MHz
0v    5.000 003  54
1v    5,000 002 59
2v    5.000 001 57
3v   5.000 000 55
4v    4.999 999 53
5v    4.999  998 51
6v    4.999 997 35

Voltage for exactly 5Mhz output  = 3.5413v

So the oscillator looks good and the fact that the Z3816  doesn't lock 
with that in
place suggests that some of those damaged  parts are needed :-(.

Have another of Ebay fluke seller's MTI 260-0664  ordered. The original 
is in the
Z3816 and don't want to take it out  again until i'm sure that it's 
necessary. At
~$18 each, it good to have  a spare and will characterise that on arrival 
to see what
the  differences are between that and the 260-0558. Knowing my luck, 
probably  find
the efc is the opposite sign, or negative, but time will  tell.

Have posted this to the list as well, in case the info is  useful...



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