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

[Bob Camp]

Hi

The electrolytic caps in these units are indeed the “weak link”. Turns out that the combination of voltage, temperature, and ripple current ratings on the typical “factory” parts are really not what they should be. First step on a “new to you” unit should be to replace them all. If they haven’t failed yet, they will fail soon :) :).

Out of a pile of (cheap) “dead units”, a bit over 3/4 of them went from non-function to fully locked up and running right just by replacing the caps. 

If that doesn’t do the trick, the next trick on most telecom Rb’s is to get the VCXO back where it should be. On some designs it will drift far enough that the lock process does not work correctly. No, that does not explain the lack of sweep on this unit. It’s simply the next most likely thing on the repair list. 

Past that you are off into some really (not) fun circuit tracing and troubleshooting. Sorry about that ….

Bob



> On Apr 24, 2024, at 12:08 PM, Razvan Popescu via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Hello,
> 
> I also had the same issue with mine and I replaced the 4 electrolytic
> caps. As you see also in the teardown pictures they are rated 105
> degrees C. I bought 125 degrees C version. After replacing the 4 caps it
> locks in around 2 minutes and stays locked. Get high quality caps
> because the physics package is quite hot and it will shorten the life of
> the caps very fast if you replace it with cheap ones.
> 
> I hope that's the only problem and you can fix your LPFRS module.
> 
> 73!
> Razvan
> 
> On 24/04/2024 16:32, VE7HR via time-nuts wrote:
>> 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
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com
>> To unsubscribe send an email to time-nuts-leave at lists.febo.com
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com