[time-nuts] Temex LPFRS-01 / LPRO rubidium reference repair

Gerd v. Egidy lists at egidy.de
Sun May 26 15:12:59 EDT 2013

Hi Ed,

> I don't have an LPFRS, but if I'm reading the manual correctly, the
> fourth column of numbers on the 'M' command (4D, 4C on your screen
> capture) is the VCXO control voltage.  Shouldn't this be continuously
> sweeping up and down until it finds lock?

You are right, it sweeps the control voltage up and down and the output 
frequency changes. But that is only happening during warmup. Once the unit had 
this short lock for a few seconds, it stops sweeping and does not start again 
even after losing the lock. Maybe a firmware issue not taking aging into 
account or something.

The terminal output in my screenshot is from the time after the short lock, so 
you don't see any sweeping in it.

> Does the output frequency
> sweep up and down and is 10 MHz somewhere in the sweep?

It sweeps and is near 10 MHz, but I don't know if 10 MHz is within the 
sweeping range or just near it. Unfortunately I don't have another reference 
reliable enough to tell - that was why I bought this unit in the first place...

Bobs suggestion in the other posts goes in the same direction.

There is a trimmer cap and several trimpots on the board. I think I'll take a 
look at the board and try to figure out what exactly they are doing before 
trying to tweak them.

> The first column (Photocell DC voltage) shows that you've
> got lots of light from the lamp.

That is why I have hope to fix this thing, a burnt out lamp would be hard to 

Kind regards,


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