[time-nuts] FRK-L Rubidium
Tom Miller
tmiller at skylinenet.net
Mon Feb 11 17:30:09 UTC 2013
It is possible to open the can if you are careful. A good vacuum desoldering
tool is a good start to remove as much of the solder as possible. Then one
would peal the can open a bit at a time. Then you need to find out where the
failure is.
But to answer your question, yes just buy one, it's much easier. But first
check that there is power to the heater.
----- Original Message -----
From: "Garren Davis" <garren.davis at qlogic.com>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Monday, February 11, 2013 12:01 PM
Subject: Re: [time-nuts] FRK-L Rubidium
Ed, Bob,
This morning I noticed the crystal control voltage was down to 11 volts.
I'll let it keep running to
see if it drops any further. The tuning capacitor is adjusted out about as
far as I want to set it. Any
further and I think the adjustment screw will fall out. I did remove C11 as
an experiment to see what
it would do to the frequency. It dropped a lot so now I know I can put a
smaller one in if I need more
adjustment.
Next up is the Tbolt. I'm pretty sure the oven heater is not working. Has
anyone taken apart the trimble
oscillator? It looks like it's sealed pretty good. I see quite a few for
sale. Is it just easier to
replace it?
Thanks for all the help.
Garren
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Ed Palmer
Sent: Sunday, February 10, 2013 11:02 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] FRK-L Rubidium
Hi Garren,
Yes, you're right. Silly me, I made the mistake of believing what was
written in the manual which says 2-12 volts. When I measure it, I see
~2-16 volts. Let that be a warning to you. This isn't the first time that
manual has led me astray! I should have known better.
Did you notice that the voltage changes as you adjust the capacitor on the
side? If the adjustment is at it's limit, you may have to change capacitors
A3C11 and maybe A3C12 to get the oscillator back on frequency. It's
explained in the manual. :-) Let it settle for at least a few days and see
which direction the crystal control voltage moves. If it falls you're fine.
If it rises higher, you may want to look at the capacitors. If you have to
change the capacitors, be sure to use NP0/C0G type capacitors.
Bob's comments regarding the C-field are right on the money. It's for fine
tuning after you have a stable lock. It won't help you obtain or maintain a
lock. You won't be able to adjust it without a known, stable
10 MHz reference source like the Tbolt and some good measurement equipment.
Ed
On 2/10/2013 9:27 AM, Garren Davis wrote:
> Hi Ed,
>
> The voltage swings from 2v to 17v. Doesn't that mean I have about 4 to 5
> volt margin if it's locked at 12 volts?
>
> I had to adjust the capacitor out almost all the way to get it to lock. If
> I need to adjust it more can I use the C-field adjustment or should I stay
> away from that?
>
> Garren
>
>
> On Feb 9, 2013, at 10:48 PM, "Ed Palmer" <ed_palmer at sasktel.net> wrote:
>
>> Hi Garren,
>>
>> Congrats on your repair. Since the crystal control voltage is spec'd as
>> ~1 to 12 Vdc, you're apparently holding onto lock by the narrowest of
>> margins. You definitely want to adjust the oscillator to bring that
>> voltage closer to the middle of it's range.
>>
>> Ed
>>
>> On 2/9/2013 11:38 AM, Garren Davis wrote:
>>> Found my problem with the FRK. R31 on the Osc board was burned and open.
>>> This was caused by a shorted C16. Replaced and it is now locked. The
>>> lock voltage is 12.7v. Is this good or should it be lower?
>>>
>>> Garren
>>>
>>> On Feb 9, 2013, at 6:10 AM, "Bob Camp" <lists at rtty.us> wrote:
>>>
>>>> Hi
>>>>
>>>> How old is the FRK? Does it look like it's been run without a heat sink
>>>> for very long? They tend to get flaky if run for a while (many months)
>>>> without heat sinking. There's nothing mysterious about it. The MTBF of
>>>> the parts gets noticeably worse as the unit heats up.
>>>>
>>>> Bob
>>>>
>>>> On Feb 9, 2013, at 1:09 AM, Garren Davis <garren.davis at qlogic.com>
>>>> wrote:
>>>>
>>>>> Well for some reason the 10 Mhz stopped working on the FRK. Don't know
>>>>> why. Started up the thunderbolt. It acquired satellites but then the
>>>>> DAC voltage went to -5 volts. It's been there for an hour. Will this
>>>>> change after the unit stabilizes? Going to bed. Will check it
>>>>> tomorrow.
>>>>>
>>>>> Garren
>>>>>
>>>>>
>>>>> On Feb 8, 2013, at 8:25 PM, "Ed Palmer" <ed_palmer at sasktel.net> wrote:
>>>>>
>>>>>> Hi Garren,
>>>>>>
>>>>>> I suggest that you get the Thunderbolt working first. Without a
>>>>>> known 10 MHz source to compare to, you're flying blind. Once the
>>>>>> Tbolt is running, you should be able to check the frequency of the
>>>>>> FRK by feeding both into your scope. Trigger on the Tbolt and watch
>>>>>> what the FRK does. You should see the trace scrolling in one
>>>>>> direction, then slow down, then stop, then scroll the other
>>>>>> direction. The 'stop' point is at 10 MHz. The frequency sweeps a
>>>>>> total of 20-30 Hz so it's easy to see. If you don't see the 'stop'
>>>>>> point, the FRK isn't getting to 10 MHz. Now use the best frequency
>>>>>> counter you've got to measure the Tbolt. Regardless of the
>>>>>> calibration of your counter, the number your counter gives you
>>>>>> becomes your 'new' 10 MHz. Now measure the FRK to see if it's
>>>>>> running fast or slow.
>>>>>>
>>>>>> You should check the temperature of the lamp. It's easy to get at by
>>>>>> removing the cover in the center of the heat sink. Probably best to
>>>>>> remove the cover and then power down before you go poking around
>>>>>> inside! The temperature of the cavity is also important, but getting
>>>>>> to it is more of a hassle - don't go there if you don't have to.
>>>>>>
>>>>>> Of course, check for the normal things like internal power supply
>>>>>> voltages, ripple, current drain (both initial and steady-state), etc.
>>>>>>
>>>>>> Regarding your second message, yes, the adjustment under the heat
>>>>>> sink near the edge is the C-field. That won't help you at this
>>>>>> point. The adjustment in the center of one side is the VCO. You
>>>>>> could try adjusting it, but like I said, you're flying blind at this
>>>>>> point. You won't know if you're adjusting closer to 10 MHz or
>>>>>> further away.
>>>>>>
>>>>>> Good luck,
>>>>>>
>>>>>> Ed
>>>>>>
>>>>>>
>>>>>> On 2/8/2013 6:12 PM, Garren Davis wrote:
>>>>>>> Been lurking on the list for a while and finally started playing
>>>>>>> with a FRK-L rubidium frequency standard. I've had this thing for a
>>>>>>> while and decided to power it up and see what it would do. I do not
>>>>>>> get a lock. What I see is the lamp voltage at 8.54 volts which I
>>>>>>> think is good but the xtal control voltage swings from 2 volts to 15
>>>>>>> volts and back to 2 volts and keeps cycling like that. I don't have
>>>>>>> a good frequency counter but I have a 3 Ghz 40 G/sample scope and it
>>>>>>> shows that the 10 MHz signal is there. I just don't know how
>>>>>>> accurate it is. Has anyone seen a problem like this? Can anyone
>>>>>>> point me to a place to start debugging this? I have the schematics
>>>>>>> and test tools. I am a test engineer so I'm not afraid to poke
>>>>>>> around in the guts of this thing. Hopefully I can get this thing
>>>>>>> running. I also have a thunderbolt that I'll get running this
>>>>>>> weekend. I don't know how deep I'll get into this time-nuts thing
>>>>>>> but I have this nice scope and a Wavecrest sitting in my gara
ge and I
'd like to put them to use. Any help would be appreciated.
>>>>>>> Garren
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