[time-nuts] Efratom FRK - no 10Mhz oscillator

Don Lewis dlewis6767 at austin.rr.com
Tue Dec 20 18:13:50 EST 2011


Thank you all for your help this afternoon.  Good ideas.  I better hope the
crystal is good and just concentrate on the discrete.

 I'll continue to investigate.  The oscillator won't oscillate on its on,
....but if I 'force' a 10MHz signal either on the collector of Q3 or even
touch the crystal oven with the 10MHx signal, ...it will oscillate and
amplify and deliver a signal.  Must be a cap or perhaps the inductor in the
10MHz circuit.


-Don









-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Azelio Boriani
Sent: Tuesday, December 20, 2011 3:01 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Efratom FRK - no 10Mhz oscillator

10MHz crystals used in OCXO are designed for the temperature of the oven so
it is not possible to find an off-the-shelf suitable crystal. Better find a
crystal coming from an OCXO.

On Tue, Dec 20, 2011 at 7:10 PM, Peter Bell <bell.peter at gmail.com> wrote:

> Hi, Don
>
> It's been quite a while since I worked on a FRK, but from what I
> remember the only signals going to that oscillator board are power and
> the control voltage. It might be worth checking the control voltage to
> see if it's at a plausible value (nominal is 5V, spec range is 1V-16V,
> IIRC) - if you have a spare xtal around, just try connecting it to the
> pins on the PCB and see if it starts up.
>
> I'm not aware of the xtals being failure prone - I have seen one FRK
> with a bad one, but having seen the condition of the system it was
> removed from, that was clearly impact damage.
>
> Regards,
>
> Pete
>
>
> On Wed, Dec 21, 2011 at 1:29 AM, Don Lewis <dlewis6767 at austin.rr.com>
> wrote:
> > A little help, pls, from the more experienced.  This is my first time
> into
> > one of these .I have listened and learned from you' all for some time,
> > though.  It can be intimidating in this close-packed FRK.
> >
> >
> >
> > I am trying to bring up an Efratom FRK  I have had for a while.
> >
> >
> >
> > The 10 MHz oscillator does not start upon power on.
> >
> >
> >
> > Any ideas where to look?
> >
> >
> >
> > I have done the following:
> >
> >
> >
> > *       I have it opened-up and applied 24vDC and the current starts up
> > initially at 1.45 amp and slowly goes down to ~.6- .8 amps.
> > *       Since I have no 10 MHz output, .so I looked at the oscillator
> board
> > and nothing out from it.
> > *       The 17 volt dc supply-rail is good, and the VCO input signal to
> the
> > varacter control-circuitry is constantly ramping up and down slowly
> between
> > ~1volt and ~15 volts.
> > *       All the transistors in the oscillator circuit seem ok with a
VOM,
> > ..and when I purposely inject a 10Mhz signal into the collector of the
> > 'oscillator' transistor (Q3), .I do get a clean 10Mhz out of the unit
(of
> > course it won't lock), .and I haven't even been into the rest of the
> unit.
> > *       I think the crystal is bad, .I took the cover off the crystal
> oven,
> > it 'looks' ok, . and the crystal heater in the oven is heating and
> > regulating.
> >
> >
> >
> >
> >
> > Any ideas?  .does the 10 MHz crystal in these have a history of failing?
> >
> > Can I get a replacement  crystal for it easily?
> >
> > How can I test this crystal for pass/fail?
> >
> >
> >
> > Thanks, .just my first test of the waters as a fledging time-nut.
> >
> >
> >
> > Don Lewis
> >
> > Austin, TX
> >
> > _______________________________________________
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