[time-nuts] Re: TEMEX LPFRS-01 LPRO repair

[paul swed]

Dave I don't own one of these. But do figure out the caps before adjusting.
There should be multiplier caps and such that in general stay very clear of
them.
Unless you have all of the stuff to adjust them. Spectrum Anaylzer....
Start the system up and see if it sweeps. you may have responded to that
and I missed it.
Paul

On Sat, Apr 27, 2024 at 4:08 AM VE7HR via time-nuts <
time-nuts at lists.febo.com> wrote:

> Changing the 4 47 uF 63V caps did not change anything.
> I tested the old ones and my Sencore LC 102 said they were good so I was
> not surprised.
> I will log data from a cold start tomorrow to see if that tells me
> something. It does lock for a bit from a cold start and when locked the
> numbers look believable. But I certainly am not seeing the sweeping on the
> Control voltage but it does change when it locks.
>
> This unit has a sticker on it saying Pin 7 is not connected. That’s the
> analog adjustment input.
>
> When I had it apart I was unable to see any trimmer caps on the board.
> Where should I be looking? There were a few trimmer pots and a couple of
> tuning cans.
>
> It’s not clear to me but what frequency am I supposed to be adjusting?
> The 10 MHz output frequency that is on some units adjusted by the external
> trimmer on pin 7 or something else. ?
>
> I will have to check calibration but I think the unit outputs a signal
> that is 249 mHz low in frequency.  I did not have a chance to see if that
> changes when it briefly locks.
>
> Thanks
> Dave
>
> Sent from my iPad
>
> > On Apr 25, 2024, at 10:37 PM, Hans Georg Lehnard via time-nuts <
> time-nuts at lists.febo.com> wrote:
> >
> > Hi Dave,
> >
> > I suggest recording the data from the serial interface and displaying it
> in a diagram.  I did this with my Temex MCFRS-01 at 1s intervals and it
> looks like the attached picture.
> >
> > The manual says:
> >
> > 1. Rb Signal level.
> > During warm-up time this signal is approximately 0V and after it
> stabilises to a nominal value of 1 to 3.3V.As
> > long as this signal is too low (<0.6V) the internal LPFRS control unit
> sweeps the Xtal frequency in order to
> > find the Rb absorption dip.
> >
> > 2. DC-Voltage of the photocell
> > this signal corresponds to the transmitted Rb light level.
> > This is the light of the Rb lamp which is partly absorbed by the Rb cell.
> > The nominal photocell voltage is in the range 2.0 to 3.5 V but must stay
> stable after the warm-up time.
> > The photo cell voltage is related to the internal reference 5 V voltage.
> > The full scale corresponds to the coded value ‘00’ and the zero (no
> light) corresponds to the coded value ‘FF’
> >
> > hgl
> >
> >
> >> Am 24.04.2024 um 16:32 schrieb VE7HR via time-nuts:
> >> I have been having lots of enjoyment out of my TinyPFA. It’s so small,
> easy to carry and quiet compared to my HP 5370B.
> >>
> >> I am testing it out on my existing pile of frequency sources. One of
> them is a LPFRS-01. It no longer locks. It locked for a few minutes when I
> first powered it up.
> >>
> >> Looking in the archives there has been a long standing thread on
> repairing these devices with several people in the same spot I am in on a
> used to work LPFRS-01.
> >> It no longer locks.
> >>
> >> Output from Serial port on mine is
> >> 8A 1C C3 8A 7C 86 A7 DC
> >> The 4th column is the VCO control voltage that should be sweeping when
> unlocked. So that is what the other threads seem to indicate.
> >>
> >> There are some nice teardown pictures of a unit at
> https://egidy.de/temex_lpfrs_lpro/
> >> With similar data output.
> >>
> >> I don’t think I have found any service information yet. If I have
> missed it please point me in the right direction.
> >>
> >> I have not pulled my unit apart bit I am not seeing the trimmer cap
> that has been speculated to be the fix in the pictures.
> >>
> >> Can anyone shed any light on what to twiddle?
> >> If I get it fixed I promise to post my results. It’s somewhat puzzling
> that there is a common question but no answer. Does this mean not one has
> fixed it or just not one has told us they have.
> >>
> >> Dave
> >> VE7HR
> >> Sent from my iPad
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> > <Rb_1265_OK.JPG>
> > <Temex_LPFRS_Manual.pdf>
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