TEMEX LPFRS-01 LPRO repair
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
Dave I agree on the sweeping. If the units not doing that there is some
other failure.
A way to check that would be let the system warm up as usual. Then unplug
wait 10 sec. Then repower.
You should see the sweep.
Two things will happen it sweeps and stops as it finds the signal and then
locks.
Or it locks to some low noise crud that doesn't allow the lock to trip.
Paul
WB8TSL
On Wed, Apr 24, 2024 at 10:53 AM VE7HR via time-nuts <
time-nuts@lists.febo.com> 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
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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
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hi Dave,
Do you get a halfway decent "on frequency" 10 MHz frequency out of the LPFRS? There is only so much capture range, so if the XO is too far off from the nominal frequency the LPFRS will never lock to Rb. I encountered this with an Efratom FRK in which the crystal heater had failed. Fixed the heater: locked ok.
Worth checking I guess.
Wilko
On 24 Apr 2024, at 16:54, VE7HR via time-nuts time-nuts@lists.febo.com 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
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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@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
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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:
-
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. -
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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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@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:
-
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. -
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
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<Rb_1265_OK.JPG>
<Temex_LPFRS_Manual.pdf>
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Hi
The oscillator that generates the 10 MHz is a VCXO. It needs to have a tuning range that “includes” the correct frequency. The sweeping process is trying to line the VCXO output up with the correct Rb “notch" frequency. The key word there is correct, there are other nearby “notches" that you don’t want to lock up on. Just how the VCXO is set up depends a lot on various subtle parts of the Rb’s design.
The adjustment pins on the unit drive the C field on the physics package. As that magnetic field changes, the notch frequency changes. When it does, the locked VCXO output moves as well. If you can tune the unit with the normal controls … it’s locked.
These telecom Rb’s don’t come with much documentation. Field repair was not part of the plan. If one broke, you sent it back to the factory and they did whatever to make it work or they replaced it with a new one. Things like schematics pretty much don’t exist for any of the modern parts ( = parts designed in the last three decades …). Even things like test point definitions or alignment procedures … not so much.
If you get into actual debugging or realignment, your first step typically is to start tracing out circuits and figuring out what’s what. Various folks have tried this on various models. Often they then find out that there are lots of board revisions, even on the same model part.
If your unit is 0.249 Hz low, that’s - 2.49 x 10^-8. Typically these Rb’s have an electrical tune range < 1x10^-8. With fancy digital synthesizers, the digital tune range could be pretty large. Either way, that’s pretty far off for an Rb.
Fun !!!
Bob
On Apr 27, 2024, at 2:04 AM, VE7HR via time-nuts time-nuts@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@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:
-
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. -
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>
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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@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@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:
- 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.
- 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
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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