[time-nuts] LPFRS phase ripple: success!

[Matthias Jelen]

Hello Time-Nuts,

I opened the LPFRS and removed the 4 electrolytic caps. One was 
completely dead. After I swapped them to new ones, everything worked 
fine. The phase ripple disappeared, the unit is now on par with the 
second one (or beyond my measurement capabilities...).

So, I highly recommend this to every owner of a used LPFRS - it takes 
about 10 minutes.

Thanks again for all the hints and have a nice weekend,

Matthias

Am 25.05.2017 um 12:46 schrieb Bob kb8tq:
> Hi
>
>
>> On May 25, 2017, at 4:12 AM, Matthias Jelen <Matthias.Jelen at gmx.de> wrote:
>>
>> Hi Angus,
>>
>> thanks for the hint. I read through this fairly long thread - the baseline seems to be: Replace the caps.
>>
>> Best regards,
>>
>> Matthias
>
> That’s what worked for mine ….. (at least most of them). In my case they arrived dead.
>
> Bob
>
>> Am 23.05.2017 um 21:44 schrieb Angus:
>>> Hi,
>>>
>>> If you've not already looked, it would be worth checking on the
>>> EEVblog since there were some discussions there on faults in these
>>> units - particularly the capacitor and lamp voltage issues.
>>> One of the temperature controllers could be a little unstable too.
>>>
>>> Angus.
>>>
>>>
>>> On Tue, 23 May 2017 09:40:26 +0200, you wrote:
>>>
>>>> Hello Time-Nuts,
>>>>
>>>> i´ve been playing with some Rbs recently.
>>>>
>>>> I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
>>>>
>>>> Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
>>>>
>>>> Any hints are appreciated.
>>>>
>>>> Regards,
>>>>
>>>> Matthias
>>>>
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