[time-nuts] FRK-L Rubidium

Garren Davis garren.davis at qlogic.com
Sat Feb 9 12:38:04 EST 2013


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 garage a
> n
>> d
>>> I'd lik
>>> e to put them to use. Any help would be appreciated.
>>>>
>>>> Garren
>>>
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>>
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