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

[Hans Georg Lehnard]

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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