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

Peter Bell bell.peter at gmail.com
Wed Dec 21 06:28:22 EST 2011


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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