[time-nuts] Temex LPFRS-01

Wed Apr 18 10:25:33 UTC 2012

I'm not using the analog input but the serial port, yes, this doesn't
improve the 1E-11 step but at least I skip the first A/D conversion. The
direct access to the C-field control seems necessary but I like to have my
stuff in the original state. My LPFRS is very rusty so I can drop my "keep
it original" rule.

On Wed, Apr 18, 2012 at 10:29 AM, MailLists <lists at medesign.ro> wrote:

> That would be the tougher part, as, with highest probability, the external
> analog adjustment is first AD converted in the MPU (AIN4) summed with the
> internally stored fine adjustment value, and then applied to the C-Field
> correction, through an external DAC8800.
> As both conversions are 8 bit, the obtained resolution of 1E-11 is
> insufficient to discipline the unit with enough accuracy, it was just meant
> to adjust the working frequency.
>
> In the last day of the easter holidays I opened one up, and now I'm trying
> to grasp the inner workings... time allowing.
>
>
> On 4/12/2012 7:50 PM, Azelio Boriani wrote:
>
>> Interesting... have to check my LPFRS now: only tested for the lock
>> indicator when received and then put aside to complete first the
>> "discipliner".
>>
>> On Thu, Apr 12, 2012 at 5:00 PM, MailLists<lists at medesign.ro>  wrote:
>>
>>  Well, the saga continues...
>>> A replacement part (for which a thorough check was specifically asked)
>>> has
>>> arrived. It boasts a "Checked OK" written with a marker pen on the label.
>>> Promising...
>>> With high expectations, the necessary connections were made, power
>>> applied, and after warming up it locks at precisely 9.999,817,1 MHz...
>>> bummer.
>>> Sometimes, for (yet) unknown reasons, it unlocks again, and, if the
>>> frequency adjustment trend is upwards, it locks again at ~10.000.000 MHz.
>>> The lock signal is active even at higher temperatures - that's quite
>>> better
>>> than the first unit, but after a power cycle the story repeats... mostly
>>> the wrong frequency comes out, but, on the brighter side, it's locked.
>>>
>>>
>>> On 3/18/2012 10:26 AM, MailLists wrote:
>>>
>>>  Yes...
>>>> Thank you, and the others, for the suggestions for cleaning/reviving the
>>>> unit, but I can't recommend to my friend to keep a pile of rust (if
>>>> water damage really is the problem) advertised as an used working item.
>>>>
>>>> Regards,
>>>> bbg
>>>>
>>>>
>>>> On 3/17/2012 4:10 PM, Azelio Boriani wrote:
>>>>
>>>>  LPFRS from fluke.l? OK, then open it up and clean it, the LPFRS from
>>>>> fluke.l suffers from high humidity/water immersion and usually are very
>>>>> rusty inside. I have received one that was very bad but after cleaning
>>>>> with
>>>>> tetrachloroethylene (translated with google) it is working properly,
>>>>> maybe
>>>>> it will fail soon but now works. I complained with fluke.l and he
>>>>> refunded
>>>>> me without asking to ship back the LPFRS.
>>>>> TIP: handle with extreme care an opened LPFRS, there is a flexible PCB
>>>>> that
>>>>> holds the DB9 connector that can tear in the corners.
>>>>>
>>>>> On Sat, Mar 17, 2012 at 10:59 AM, MailLists<lists at medesign.ro>  wrote:
>>>>>
>>>>>  Hello all,
>>>>>
>>>>>>
>>>>>> a friend purchased from the bay a<subj.>  in the LPRO configuration.
>>>>>> After
>>>>>> some problems encountered during the first power ups, he asked for
>>>>>> help -
>>>>>> I'm passing the questions further...
>>>>>> After about 9 minutes of warm-up from room temperature (22°C) the lock
>>>>>> signal goes low, but after a short time starts to switch low/high with
>>>>>> decreasing low periods, until it remains high with short low pulses,
>>>>>> spaced
>>>>>> at about 2 seconds. After power-down, and sufficient cooling time, the
>>>>>> cycle repeats.
>>>>>> First step was to reapply the thermal interface to the integrated Al
>>>>>> radiator, which helped a bit, the time during which the unit is locked
>>>>>> growing slightly.
>>>>>> Next step was forced cooling, which helped more, so the lock loss
>>>>>> could be
>>>>>> attributed with high probability to elevated operating temperatures.
>>>>>> The
>>>>>> temperature of the base plate (integrated Al radiator) at which lock
>>>>>> gets
>>>>>> lost is about 40°C, so for a reasonable operation it should not pass
>>>>>> about
>>>>>> 36°C, at which the power consumption raises to about 17W. That also
>>>>>> means
>>>>>> that for a 1°C/W heat sinking - obtainable with a larger passive HS or
>>>>>> active cooling - operation above 30°C ambient gets practically
>>>>>> impossible
>>>>>> (except refrigeration, Peltier, etc.).
>>>>>>
>>>>>> Any further help or suggestions are welcome.
>>>>>>
>>>>>> Regards,
>>>>>> bbg
>>>>>>
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