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

Peter Bell bell.peter at gmail.com
Wed Dec 21 10:41:49 EST 2011


Hi, Don

If the xtal is bad, you will really have to try and find one that's
designed to work at whatever temperature the oven is set to (65c, I
think..) - trying to put a regular xtal in there that was designed for
room temperature operation will likely not work since it will run 8-10
ppm high and have a very poor tempco.

I'm not sure what the load capacitance of the original xtal was, but
you could guesstimate it based on the load capacitance of your test
xtal and seeing how close to the right frequency you get.

Regards,

Pete


On Wed, Dec 21, 2011 at 10:04 PM, Don Lewis <dlewis6767 at austin.rr.com> wrote:
> Thanks, Pete.
>
> Good tips.
>
> I ordered 10 crystals this morning, ...they are dirt cheap.  Will try and
> test one as you suggested.
>
> If it is the 'crystal', a bad crystal, .......what then?
>
> Do I try to place one of these cheap ones in the oven, ...or do I try to
> just run it outside the oven or find a high-temperature crystal???
>
> The crystal oven/controller seems fine, ...hot enough to hurt my fingers.
>
> Thanks, ...-Don
>
>
> ------------------------------------------
>
>
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Peter Bell
> Sent: Wednesday, December 21, 2011 5:28 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Efratom FRK - no 10Mhz oscillator
>
> Yeah, that was why I suggested just sticking a random 10MHz xtal
> across the pins on the board (with the existing xtal wiring
> disconnected) - if the rest of the circuit is good, then the
> oscillator should start up with no problems - if it doesn't, then
> suspect a fault somewhere else.  I just pulled out the manual, and I
> would start by lifting the connection on E7, and connecting a 10MHz
> xtal in series with a 10pF cap between the E7 pin and ground.  This
> will bypass both the xtal and the frequency adjustment circuit.  If
> that doesn't work, then the oscillator circuit is the problem - if it
> does work, then remove the 10 pF cap and connect the xtal directly
> between E7 and E8 - if it still works, it's almost certainly a bad
> xtal.  If it worked with the 10 pF cap but not with the E8 connection,
> then check the control voltage (E9: 0.5V-17V) - if that looks good,
> then suspect the frequency control circuit.  If it's bad, then try
> hooking it to +5V to verify the oscillator and then troubleshoot the
> servo board.
>
> Regards,
>
> Pete
>
>
> On Wed, Dec 21, 2011 at 5:00 AM, Azelio Boriani
> <azelio.boriani at screen.it> wrote:
>> 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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