Repair lpro-101 no lock

[kjk24]

Hello,

 the lpro-101 rubidium Oszillator.  i diside to buy a unit and try my luck !. But my one dose not lock like hundered others.
Try now to fix that thing, read alot websides also the pdfs Form some people how did the same before with gold explanations, but my unit has other isuss i think. May someone here like to help me and other people with the same or simular Problems.

heater for lamp is ok
Heater  for gravity is OK
Lamp light to dark ? I have no Referenz how bright it must shine , Frequenz is around 150mhz to high ? Has some one the exact frq.
9..GHz are there
Photocell and AMPlifier i can measure around 9v in the tstpin using a pocket light into the gravity box
10mhz osz is at the output pin available
Lock Indikator pin is high and dont go low

My first question has anyone a schematic 

Best regrads
Kai

[TSL]

All the detail you need can be found here...

http://www.ko4bb.com/manuals/index.php?dir=02_GPS_Timing/Efratom

[kjk24]

Thank you i know the page, but i csn find the information what iam asking for,
the frq of the lamp oscillator.
I found 60 to 100mhz 80, 70, .
has anybody messured that  ting in a running unit ? Please let  me know. A understanding question if the oscillators frequency  is not correct but the lamp is shining is the rubidium generated light frequenz also changing ?
or  just less lumen ?

[TSL]

Thank you i know the page, but i csn find the information what iam asking for,
the frq of the lamp oscillator.
I found 60 to 100mhz 80, 70, .
has anybody messured that  ting in a running unit ? Please let  me know. A understanding question if the oscillators frequency  is not correct but the lamp is shining is the rubidium generated light frequenz also changing ?
or  just less lumen ?

You need to read the LPRO manual, in particular, the "Theory of Operation" section.

If you don't understand that section, you're going to have difficulty in repairing your unit.

A common fault with many rubidium standards is that the rubidium tends to get splattered all over the envelope of the lamp instead of in the pinch. This is simply fixed by extracting the lamp and heating with a heat gun until the rubidium is reconstituted down in the pinch.

This problem and many other common faults associated with the physics package, and their repair, are detailed in two of the documents I've pointed you at...

This document lists common faults, their repair, and appropriate measurements to satisfy yourself that a component part is working
http://www.ko4bb.com/manuals/101.191.132.19/Efratom_LPRO_Repair_Guide.pdf


This document details how to rejuvenate the rubidium lamp...
http://www.ko4bb.com/manuals/101.191.132.19/Efratom_FRS_Lamp_assembly_repair.pdf

While it talks about the FRSC rather than the LPRO, the procedure is the same.

As I posted previously, all the information you require, is in these documents.

[TurboTom]

I'm in a similar situation - gave a go on an LPRO-101 that was told not to lock. Well, the price tag was very attractive so I took a chance. Today it dropped in and I immediately powered it up. Initially, everything looked good, voltages all where they should be and lamp condition indicator voltage at 7V. But the damn thing wouldn't lock and the frequency kept on modulating up and down at slow pace. Finally, I was able to narrow down the problem to the step recovery diode inside the cavity. Through the threaded hole of the cavity tuning screw I was able to measure at the joint of the load resistor (inductor??) and the SRD and confirmed that the diode is open-circuit. Bummer! As I'm aware there's no way to open the cavity with the slightest chance to close it again without massively de-tuning it (or maybe even breaking other things inside). My approach will now be either sourcing another damaged LPR-101 with hopefully a different fault or to try to attach an SRD externally and hope that the capacity of the RF feed-trough is low enough not to attenuate the GHz signal too much... I'll report my findings.
At least removal of the rubidium cell / resonator unit offered the opportunity to take a nice shot of the lit plasma lamp!

Cheers,
Thomas

[kjk24]

Hi Thomas,

perfect someone how like to repair it and share what he do ! , i have one with i guess a working diode, but i think my lamp is to dark.
as i discribed i can messure with my spectrumana. the rubidium frq at the cells housing.

what can i post for you ?
how can we compare the bridghtness of the lamp ? to have a indicator that the lamp amp. & lamp lumenoutput are ok.

fyi
my transistor for the lamp are dead at the moment, i test a little to much  , i have to buy a new MRF160 first or equivalent

 
 

best regards
kai

[alank2]

If anyone has a dead lpro, I'd love to have a spare lamp.  I thought mind was getting down to 3.5V or so, but that was what a different pcb reported.  It is around 5V when measured with a meter directly.  I tried the rejuvenate it, but it only went up a little bit.

[TurboTom]

Kai-
to answer your question regarding the frequency - on my board the lamp excitation oscillator runs at 96.7MHz when the lamp is warm and everything's stationary. Initially it's one or two MHz higher. That's bad luck with your lamp exciter transistor, these beasts are not particularly cheap and quite awkward to replace.

Meanwhile I've been able to remove the SRD network from my sick '101 - it's been possible to get the anode pin of the SRD free using a desoldering station and after that, just careful but ample application of heat at the ground flange of the RF feedthrough permitted to "thread" the whole network through the hole in the back wall of the cavity.

I was amazed to find that the feedthrogh is actually a capacitor of 100pF, so external installation of the SRD would have been completely useless. Moreover, so far no suitable replacement SRD is in sight so I've got a plan that may sound quite mad - but there's nothing to lose anyway: The SRD is incapsulated in a glass envelope, just like the ancient germanium diodes. Internally, the chip seems to be connected via a (molybdenum?) sheet metal spring and some kind of a small "pip" on the die itself.

If I measure the SRD at certain times / moon phases I can actually get "some" continuity readings in the passing direction but never in the blocking direction. This makes me assume that the crystal itself is still intact.

What I now intend to do is to make a small fixture to place the diode between two opposed metal shafts with tiny holes drilled centally to accomodate the terminal wires of the SRD. These shafts can be rotated by two synchonizing gears so I don't put any torsional stress on the glass envelope. This whole arrangement will be mounted vertically so the weight of one of the shafts lies on the diode body. My approach will now be to heat the glass evenely while rotating the diode, just enough to soften it slightly in order to increase the pressure on the molybdenum spring. I've got other diodes in the same mechanical package so I can figure out the required temperatures / times.

I'm quite curious if this repair approach will work -- and as said before, there's noting to lose, only experience to gain and maybe even win!

Please see three microscopic photos of the SRD network. There are the 100pF feedthrough, a 3 ohms low-inductance resistor and the SRD itself. The closeups of the SRD show its internal construction more or less clearly...

Cheers,
Thomas

[kjk24]

Hello Thomas,

good explanation of the diode, can you post pictures of the open cavity and how the diode network is placed insight.
hope you get the diode meldet insight the glass  thnx for the frequency i have ordered a new transistor from china 12$ plus shipment after replacing i will measure the frq again and try to adjust it to 96MHz , have you measured it with a oszi, counter, spectrum.. ?
can you measure the peak voltage of the coil.
SRD cant you buy a new one ? i remamber there wars a company how sell such parts in usa.

alank2
a spare lamp ! yes i ask my self why cant we build such a thing by our self, rubidium is avail from companys, but what else is insight ?
and how can put such a thing together ? i saw in youtube some people how can build tubes at home for old radios, such a dude would to the job i guess.

if i have my one runnuing again i let you know, buy the way i ordered a working one to measure that thing to know whats a must on each stage.
what i like to know how bright must be the lamp for a working unit, i will find out soon... hopefuly

best regards
kai

[TurboTom]

Kai -

I measured the frequency with a DSO and just used a coil of a few turns of magnet wire between the probe tip and probe ground, loosely inductively coupled to the excitation chamber of the rubidium lamp. I didn't want to measure directly at the exciter coil since the voltages there can be quite high (LC resonance circuit). Hence I cannot tell you anything about the voltage there.

The SRD should be available and I also tried to contact a manufacturer for a replacement part but they never replied - I think a single diode simply isn't enough business to worry about... And they didn't specify any distributors.

But the good news is - my crazy repair attempt worked! 

From some scrap metal I machined a fixture to hold the diode evenly at the two ends of its glass body and to be able to apply some moderate axial pressure. The holding pieces were accurately aligned and suspended so they could be rotated synchronously (in order to be able to apply the heat symmetrically around the circumference of the diode). The whole thing was rotated with a battery drill (a friend lent me a hand here so I could apply the heat and pressure). To heat the diode, a hot air jet from an SMD rework station at round about 500°C was used.

It took some attempts, each time admitting more temperature for some more time until finally the diode measured okay again. Then I applied approximately the same amout of heat/time that led to success once more so I could be sure the fix is permanent.

Finally, I reassembled the cavity and powered up the LPRO -- it heated up and directly went into a lock! I attached some photos of my SRD repair fixture, the last one with the hot air nozzle visible to the right. If somebody told me before that it's possible to rapair a diode that way, I wouldn't have believed it!

Mission accomplished!

Cheers,
Thomas

[Vgkid]

Impressive work 

[TSL]

Brilliant mate !
awesome work.

[lowimpedance]

Perfect example of thinking 'outside the square' when faced with a seemingly impossible situation. Stirling job and I also would not have believed it either.  .

[Theboel]

never think something like that 

[kjk24]

ive got my new MRF160, the light is on again  but no lock like before.

i measured the working unit to compare it and share the results to all.
here are the results for a loked unit:

I used 17V as input Voltage for the unit, it sucks 1.7A and 500-600mA if it locked i dont remember the exact current.
 
Lamp Voltage (connector pin 5)
8.74V
Ext C-Field (connector pin7)
2,28V
XTal VMon (connector pin 9)
6.70V

Lamp Oszilator
 
 
 
10MHz Quarz
 
 
 
cavity input
 
 
 

Rubidium Frequency from Pin Diode