JG
Julien Goodwin
Tue, Feb 1, 2022 9:17 AM
I picked up an Efratom FRT a while ago, and it finally arrived the other
day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear
someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few
days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first
stage op-amp from the photo-cell, so is this effectively an indication
that the (electrical part of the) lamp is dead? Certainly it wasn't
anywhere near the temperature it should have been when I removed the
bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up
cold with 24V, dropping down to about ~0.5A after a while. The sealed
sub-section of board A4 seems be where all the heat is, and I'm assuming
that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious
issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my
working house standard I'm somewhat loath to open it up lest I end up
with two dead units and zero working.
Any suggestions?
I picked up an Efratom FRT a while ago, and it finally arrived the other
day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear
someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few
days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first
stage op-amp from the photo-cell, so is this effectively an indication
that the (electrical part of the) lamp is dead? Certainly it wasn't
anywhere near the temperature it should have been when I removed the
bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up
cold with 24V, dropping down to about ~0.5A after a while. The sealed
sub-section of board A4 seems be where all the heat is, and I'm assuming
that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious
issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my
working house standard I'm somewhat loath to open it up lest I end up
with two dead units and zero working.
Any suggestions?
PS
paul swed
Tue, Feb 1, 2022 10:50 AM
Julien
Sorry to here.
Yes that 3V reading is telling you there is most likely no light.
The rb requires 2 things to effectively work to illuminate the photocell.
Lamp ignition and the correct lamp temp.
On less expensive units its possible to see if the lamp is lit as the
assembly pulls out and the rf assembly is still attached. Do not know if
you can do that on the FRK.
I would see if the lamp ignites and they do run hot.
Good luck.
Paul
WB8TSL
On Tue, Feb 1, 2022 at 5:25 AM Julien Goodwin time-nuts@studio442.com.au
wrote:
I picked up an Efratom FRT a while ago, and it finally arrived the other
day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear
someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few
days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first
stage op-amp from the photo-cell, so is this effectively an indication
that the (electrical part of the) lamp is dead? Certainly it wasn't
anywhere near the temperature it should have been when I removed the
bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up
cold with 24V, dropping down to about ~0.5A after a while. The sealed
sub-section of board A4 seems be where all the heat is, and I'm assuming
that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious
issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my
working house standard I'm somewhat loath to open it up lest I end up
with two dead units and zero working.
Any suggestions?
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send
an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
Julien
Sorry to here.
Yes that 3V reading is telling you there is most likely no light.
The rb requires 2 things to effectively work to illuminate the photocell.
Lamp ignition and the correct lamp temp.
On less expensive units its possible to see if the lamp is lit as the
assembly pulls out and the rf assembly is still attached. Do not know if
you can do that on the FRK.
I would see if the lamp ignites and they do run hot.
Good luck.
Paul
WB8TSL
On Tue, Feb 1, 2022 at 5:25 AM Julien Goodwin <time-nuts@studio442.com.au>
wrote:
> I picked up an Efratom FRT a while ago, and it finally arrived the other
> day, sadly it doesn't lock.
>
> The oscillator inside is an older Efratom FRK, and it's also clear
> someone had been inside already, although it does appear to be complete.
>
> The FRK manual does include a key description I wish I'd noticed a few
> days ago before full disassembly:
>
> "Terminal pin 7 provides an indication of proper operation of the
> rubidium lamp. For nominal operation the signal is 6 to 12V. An
> inoperative lamp is indicated by an signal of approximately 3V. The
> internal resistance of this circuit is approximately 6K."
>
> ... indeed I'm seeing 3v on that pin.
>
> Based on the circuit this appears to simply be the output of the first
> stage op-amp from the photo-cell, so is this effectively an indication
> that the (electrical part of the) lamp is dead? Certainly it wasn't
> anywhere near the temperature it should have been when I removed the
> bulb after running for over an hour.
>
> Just for completeness, the unit does draw up to ~0.8A when started up
> cold with 24V, dropping down to about ~0.5A after a while. The sealed
> sub-section of board A4 seems be where all the heat is, and I'm assuming
> that's an ovenised part of the crystal oscillator.
>
> I also popped the rubidium bulb out and confirmed there's no obvious
> issues there.
>
> I do have another FRK here, but as it's an FRK-LN, and it's also my
> working house standard I'm somewhat loath to open it up lest I end up
> with two dead units and zero working.
>
> Any suggestions?
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send
> an email to time-nuts-leave@lists.febo.com
> To unsubscribe, go to and follow the instructions there.
>
PB
Peter Bell
Tue, Feb 1, 2022 11:51 AM
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Start by checking if the lamp is actually striking - if not, check the 20V
supply on the lamp drive board and the
drive transistor (2N3553, IIRC) - also check that the lamp assembly is
heating up. If the temperature seems
correct and the lamp is lit then another thing to try is inspecting the
lamp to see if the Rb has managed to migrate
to places where it obstructs the light coming out of the lamp - if so,
careful heating with a heat gun can rectify
this. You want all the Rb in the bottom of the lamp.
It's been years since I worked on these things, but they were generally
pretty easy to fix - the schematics are
available and uses all standard components.
Regards,
Pete
On Tue, Feb 1, 2022 at 6:25 PM Julien Goodwin <time-nuts@studio442.com.au>
wrote:
> "Terminal pin 7 provides an indication of proper operation of the
> rubidium lamp. For nominal operation the signal is 6 to 12V. An
> inoperative lamp is indicated by an signal of approximately 3V. The
> internal resistance of this circuit is approximately 6K."
>
> ... indeed I'm seeing 3v on that pin.
>
>
Start by checking if the lamp is actually striking - if not, check the 20V
supply on the lamp drive board and the
drive transistor (2N3553, IIRC) - also check that the lamp assembly is
heating up. If the temperature seems
correct and the lamp is lit then another thing to try is inspecting the
lamp to see if the Rb has managed to migrate
to places where it obstructs the light coming out of the lamp - if so,
careful heating with a heat gun can rectify
this. You want all the Rb in the bottom of the lamp.
It's been years since I worked on these things, but they were generally
pretty easy to fix - the schematics are
available and uses all standard components.
Regards,
Pete
MW
Matthias Welwarsky
Tue, Feb 1, 2022 12:00 PM
A couple of things to check:
The FRK has a separate power supply pin for the heating elements. Be sure to
connect it.
If the lamp still doesn't light up, check the temperature of the lamp housing.
I'm afraid this won't be easy without disassembling the unit.
If the temperatures are correct, see if the exciter oscillator is working.
The lamp itself is unlikely to fail unless it's physically cracked.
Good luck.
On Dienstag, 1. Februar 2022 10:17:59 CET Julien Goodwin wrote:
I picked up an Efratom FRT a while ago, and it finally arrived the other
day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear
someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few
days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first
stage op-amp from the photo-cell, so is this effectively an indication
that the (electrical part of the) lamp is dead? Certainly it wasn't
anywhere near the temperature it should have been when I removed the
bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up
cold with 24V, dropping down to about ~0.5A after a while. The sealed
sub-section of board A4 seems be where all the heat is, and I'm assuming
that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious
issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my
working house standard I'm somewhat loath to open it up lest I end up
with two dead units and zero working.
Any suggestions?
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an
email to time-nuts-leave@lists.febo.com To unsubscribe, go to and follow
the instructions there.
A couple of things to check:
The FRK has a separate power supply pin for the heating elements. Be sure to
connect it.
If the lamp still doesn't light up, check the temperature of the lamp housing.
I'm afraid this won't be easy without disassembling the unit.
If the temperatures are correct, see if the exciter oscillator is working.
The lamp itself is unlikely to fail unless it's physically cracked.
Good luck.
On Dienstag, 1. Februar 2022 10:17:59 CET Julien Goodwin wrote:
> I picked up an Efratom FRT a while ago, and it finally arrived the other
> day, sadly it doesn't lock.
>
> The oscillator inside is an older Efratom FRK, and it's also clear
> someone had been inside already, although it does appear to be complete.
>
> The FRK manual does include a key description I wish I'd noticed a few
> days ago before full disassembly:
>
> "Terminal pin 7 provides an indication of proper operation of the
> rubidium lamp. For nominal operation the signal is 6 to 12V. An
> inoperative lamp is indicated by an signal of approximately 3V. The
> internal resistance of this circuit is approximately 6K."
>
> ... indeed I'm seeing 3v on that pin.
>
> Based on the circuit this appears to simply be the output of the first
> stage op-amp from the photo-cell, so is this effectively an indication
> that the (electrical part of the) lamp is dead? Certainly it wasn't
> anywhere near the temperature it should have been when I removed the
> bulb after running for over an hour.
>
> Just for completeness, the unit does draw up to ~0.8A when started up
> cold with 24V, dropping down to about ~0.5A after a while. The sealed
> sub-section of board A4 seems be where all the heat is, and I'm assuming
> that's an ovenised part of the crystal oscillator.
>
> I also popped the rubidium bulb out and confirmed there's no obvious
> issues there.
>
> I do have another FRK here, but as it's an FRK-LN, and it's also my
> working house standard I'm somewhat loath to open it up lest I end up
> with two dead units and zero working.
>
> Any suggestions?
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an
> email to time-nuts-leave@lists.febo.com To unsubscribe, go to and follow
> the instructions there.
BK
Bob kb8tq
Tue, Feb 1, 2022 2:00 PM
Hi
Quick couple hints on basic Rb operation:
-
The cells / lamps need to be at the proper temperatures. Oddly enough
they don’t all work when at the same temperature. There often are two oven
controllers in there to accomplish this.
-
The synthesized “interrogation signal” needs to be pretty darn close before
it tries to lock. An local oscillator that has drifted a few tenths of a ppm in the
wrong direction may be all it takes to stop things.
-
What you normally look at out of the photo diode is an audio tone. It’s the
recovered modulation on the interrogation signal. Pretty much everything needs
to be close in order to get that tone.
-
There is an RF exciter circuit that “lights up the bulb”. If it has stopped working,
you get no nice purple glow and everything comes to a halt.
Yes there is a lot more to it than that. I’m just trying to point out a few areas that
probably need to be checked before you start a deep dive into this or that.
Bob
On Feb 1, 2022, at 4:17 AM, Julien Goodwin time-nuts@studio442.com.au wrote:
I picked up an Efratom FRT a while ago, and it finally arrived the other day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the rubidium lamp. For nominal operation the signal is 6 to 12V. An inoperative lamp is indicated by an signal of approximately 3V. The internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first stage op-amp from the photo-cell, so is this effectively an indication that the (electrical part of the) lamp is dead? Certainly it wasn't anywhere near the temperature it should have been when I removed the bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up cold with 24V, dropping down to about ~0.5A after a while. The sealed sub-section of board A4 seems be where all the heat is, and I'm assuming that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my working house standard I'm somewhat loath to open it up lest I end up with two dead units and zero working.
Any suggestions?
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
Hi
Quick couple hints on basic Rb operation:
1) The cells / lamps need to be at the proper temperatures. Oddly enough
they don’t all work when at the same temperature. There often are two oven
controllers in there to accomplish this.
2) The synthesized “interrogation signal” needs to be pretty darn close before
it tries to lock. An local oscillator that has drifted a few tenths of a ppm in the
wrong direction may be all it takes to stop things.
3) What you normally look at out of the photo diode is an audio tone. It’s the
recovered modulation on the interrogation signal. Pretty much everything needs
to be close in order to get that tone.
4) There is an RF exciter circuit that “lights up the bulb”. If it has stopped working,
you get no nice purple glow and everything comes to a halt.
Yes there is a lot more to it than that. I’m just trying to point out a few areas that
probably need to be checked before you start a deep dive into this or that.
Bob
> On Feb 1, 2022, at 4:17 AM, Julien Goodwin <time-nuts@studio442.com.au> wrote:
>
> I picked up an Efratom FRT a while ago, and it finally arrived the other day, sadly it doesn't lock.
>
> The oscillator inside is an older Efratom FRK, and it's also clear someone had been inside already, although it does appear to be complete.
>
> The FRK manual does include a key description I wish I'd noticed a few days ago before full disassembly:
>
> "Terminal pin 7 provides an indication of proper operation of the rubidium lamp. For nominal operation the signal is 6 to 12V. An inoperative lamp is indicated by an signal of approximately 3V. The internal resistance of this circuit is approximately 6K."
>
> ... indeed I'm seeing 3v on that pin.
>
> Based on the circuit this appears to simply be the output of the first stage op-amp from the photo-cell, so is this effectively an indication that the (electrical part of the) lamp is dead? Certainly it wasn't anywhere near the temperature it should have been when I removed the bulb after running for over an hour.
>
> Just for completeness, the unit does draw up to ~0.8A when started up cold with 24V, dropping down to about ~0.5A after a while. The sealed sub-section of board A4 seems be where all the heat is, and I'm assuming that's an ovenised part of the crystal oscillator.
>
> I also popped the rubidium bulb out and confirmed there's no obvious issues there.
>
> I do have another FRK here, but as it's an FRK-LN, and it's also my working house standard I'm somewhat loath to open it up lest I end up with two dead units and zero working.
>
> Any suggestions?
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com
> To unsubscribe, go to and follow the instructions there.
RA
Robert Atkinson
Tue, Feb 1, 2022 9:14 PM
Is the lamp actually lighting?
The lamp mounting screw cap normally has a small hole in the center of the slot. In reduced lighting you can see a purple glow if the lamp has struck.If no light check the RF drive circuit. If light but low signal (3V) check the photocell circuits.
I fixed a faulty FRK last year with lit lamp but no signal. It turned out to be a cracked joint at the turret tag the the wire from the photocell is connected to. Check the electrolytics while you are in there.
Robert G8RPI.
On Tuesday, 1 February 2022, 10:25:42 GMT, Julien Goodwin <time-nuts@studio442.com.au> wrote:
I picked up an Efratom FRT a while ago, and it finally arrived the other
day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear
someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few
days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first
stage op-amp from the photo-cell, so is this effectively an indication
that the (electrical part of the) lamp is dead? Certainly it wasn't
anywhere near the temperature it should have been when I removed the
bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up
cold with 24V, dropping down to about ~0.5A after a while. The sealed
sub-section of board A4 seems be where all the heat is, and I'm assuming
that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious
issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my
working house standard I'm somewhat loath to open it up lest I end up
with two dead units and zero working.
Any suggestions?
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
Is the lamp actually lighting?
The lamp mounting screw cap normally has a small hole in the center of the slot. In reduced lighting you can see a purple glow if the lamp has struck.If no light check the RF drive circuit. If light but low signal (3V) check the photocell circuits.
I fixed a faulty FRK last year with lit lamp but no signal. It turned out to be a cracked joint at the turret tag the the wire from the photocell is connected to. Check the electrolytics while you are in there.
Robert G8RPI.
On Tuesday, 1 February 2022, 10:25:42 GMT, Julien Goodwin <time-nuts@studio442.com.au> wrote:
I picked up an Efratom FRT a while ago, and it finally arrived the other
day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear
someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few
days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first
stage op-amp from the photo-cell, so is this effectively an indication
that the (electrical part of the) lamp is dead? Certainly it wasn't
anywhere near the temperature it should have been when I removed the
bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up
cold with 24V, dropping down to about ~0.5A after a while. The sealed
sub-section of board A4 seems be where all the heat is, and I'm assuming
that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious
issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my
working house standard I'm somewhat loath to open it up lest I end up
with two dead units and zero working.
Any suggestions?
_______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
JG
Julien Goodwin
Fri, Feb 4, 2022 6:15 AM
Well that was unexpectedly easy (to diagnose).
Thanks all for the replies, much appreciated, you have once again
confirmed my appreciation for this group.
I sat down this evening to work through your various suggestions, and,
by chance, picked up the unit without my lab power supply (and more
importantly, its noisy fans) being on, where I heard a little rattle I
must have missed before.
Removed the bottom panel, which I hadn't done yet, and out dropped the
remnants of a Vishay RW80U 20-ohm resistor. Based on the circuit this
pretty much has to be R2 on the lamp board (following the December 73
circuit I have, which has that at 10 ohms), which is directly in-circuit
for the lamp, so would explain exactly what I've seen.
The lamp board in general seems to have a few holes missing components,
so I'm going to have to get it out which looks like a project in itself.
If anyone has any pointers to decent guides on optimum process on
further disassembly, otherwise I guess it's copious photos, notes, and
hoping I don't stuff up anything too much.
I'd also appreciate suggestions for replacement foam to use in the lamp
cavity as the original stuff has long since degraded.
Paul, Peter Robert,
Thanks for reinforcing what I'd suspected with the lamp.
Matthias,
I hadn't bothered with an actual temperature meter, luckily on the FRT
it's actually easy to confirm lamp temperature in use, and it certainly
wasn't anywhere near 100c. I think what heat there was likely leaked
through from the crystal oven, which was getting pretty hot.
Bob,
Fortunately the onboard crystal does seem likely to still be close
enough, based on what I was seeing on a counter, so I feel like I have a
hope of recovering the unit if I do manage to get the lamp going again.
On 1/2/22 8:17 pm, Julien Goodwin wrote:
I picked up an Efratom FRT a while ago, and it finally arrived the other
day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear
someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few
days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first
stage op-amp from the photo-cell, so is this effectively an indication
that the (electrical part of the) lamp is dead? Certainly it wasn't
anywhere near the temperature it should have been when I removed the
bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up
cold with 24V, dropping down to about ~0.5A after a while. The sealed
sub-section of board A4 seems be where all the heat is, and I'm assuming
that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious
issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my
working house standard I'm somewhat loath to open it up lest I end up
with two dead units and zero working.
Any suggestions?
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe
send an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
Well that was unexpectedly easy (to diagnose).
Thanks all for the replies, much appreciated, you have once again
confirmed my appreciation for this group.
I sat down this evening to work through your various suggestions, and,
by chance, picked up the unit without my lab power supply (and more
importantly, its noisy fans) being on, where I heard a little rattle I
must have missed before.
Removed the bottom panel, which I hadn't done yet, and out dropped the
remnants of a Vishay RW80U 20-ohm resistor. Based on the circuit this
pretty much has to be R2 on the lamp board (following the December 73
circuit I have, which has that at 10 ohms), which is directly in-circuit
for the lamp, so would explain exactly what I've seen.
The lamp board in general seems to have a few holes missing components,
so I'm going to have to get it out which looks like a project in itself.
If anyone has any pointers to decent guides on optimum process on
further disassembly, otherwise I guess it's copious photos, notes, and
hoping I don't stuff up anything too much.
I'd also appreciate suggestions for replacement foam to use in the lamp
cavity as the original stuff has long since degraded.
Paul, Peter Robert,
Thanks for reinforcing what I'd suspected with the lamp.
Matthias,
I hadn't bothered with an actual temperature meter, luckily on the FRT
it's actually easy to confirm lamp temperature in use, and it certainly
wasn't anywhere near 100c. I think what heat there was likely leaked
through from the crystal oven, which was getting pretty hot.
Bob,
Fortunately the onboard crystal does seem likely to still be close
enough, based on what I was seeing on a counter, so I feel like I have a
hope of recovering the unit if I do manage to get the lamp going again.
On 1/2/22 8:17 pm, Julien Goodwin wrote:
> I picked up an Efratom FRT a while ago, and it finally arrived the other
> day, sadly it doesn't lock.
>
> The oscillator inside is an older Efratom FRK, and it's also clear
> someone had been inside already, although it does appear to be complete.
>
> The FRK manual does include a key description I wish I'd noticed a few
> days ago before full disassembly:
>
> "Terminal pin 7 provides an indication of proper operation of the
> rubidium lamp. For nominal operation the signal is 6 to 12V. An
> inoperative lamp is indicated by an signal of approximately 3V. The
> internal resistance of this circuit is approximately 6K."
>
> ... indeed I'm seeing 3v on that pin.
>
> Based on the circuit this appears to simply be the output of the first
> stage op-amp from the photo-cell, so is this effectively an indication
> that the (electrical part of the) lamp is dead? Certainly it wasn't
> anywhere near the temperature it should have been when I removed the
> bulb after running for over an hour.
>
> Just for completeness, the unit does draw up to ~0.8A when started up
> cold with 24V, dropping down to about ~0.5A after a while. The sealed
> sub-section of board A4 seems be where all the heat is, and I'm assuming
> that's an ovenised part of the crystal oscillator.
>
> I also popped the rubidium bulb out and confirmed there's no obvious
> issues there.
>
> I do have another FRK here, but as it's an FRK-LN, and it's also my
> working house standard I'm somewhat loath to open it up lest I end up
> with two dead units and zero working.
>
> Any suggestions?
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe
> send an email to time-nuts-leave@lists.febo.com
> To unsubscribe, go to and follow the instructions there.
JG
Julien Goodwin
Fri, Feb 4, 2022 10:12 AM
On 4/2/22 5:15 pm, Julien Goodwin wrote:
Well that was unexpectedly easy (to diagnose).
Thanks all for the replies, much appreciated, you have once again
confirmed my appreciation for this group.
I sat down this evening to work through your various suggestions, and,
by chance, picked up the unit without my lab power supply (and more
importantly, its noisy fans) being on, where I heard a little rattle I
must have missed before.
Removed the bottom panel, which I hadn't done yet, and out dropped the
remnants of a Vishay RW80U 20-ohm resistor. Based on the circuit this
pretty much has to be R2 on the lamp board (following the December 73
circuit I have, which has that at 10 ohms), which is directly in-circuit
for the lamp, so would explain exactly what I've seen.
Or, following the FRK-L schematic[1] it is indeed a 20 ohm 2W wirewound
(R14). All the other unused holes on the PCB lack obvious signs of
component legs, so that might be it.
I shall see what I can scrounge up at the local electronics shop
tomorrow[2] to see if I can bodge enough to test, hopefully without
needing to remove the board. Glad I had new tips for my tiny precision
iron show up today, might just be possible.
1: The FRK-L seems closer in some way than the original, although in
others the original is. This is labelled an FRK-H "made in West Germany"
which certainly dates it.
2: Tens of thousands of surface mount resistors here, but almost no
through hole.
The lamp board in general seems to have a few holes missing components,
so I'm going to have to get it out which looks like a project in itself.
If anyone has any pointers to decent guides on optimum process on
further disassembly, otherwise I guess it's copious photos, notes, and
hoping I don't stuff up anything too much.
I'd also appreciate suggestions for replacement foam to use in the lamp
cavity as the original stuff has long since degraded.
Paul, Peter Robert,
Thanks for reinforcing what I'd suspected with the lamp.
Matthias,
I hadn't bothered with an actual temperature meter, luckily on the FRT
it's actually easy to confirm lamp temperature in use, and it certainly
wasn't anywhere near 100c. I think what heat there was likely leaked
through from the crystal oven, which was getting pretty hot.
Bob,
Fortunately the onboard crystal does seem likely to still be close
enough, based on what I was seeing on a counter, so I feel like I have a
hope of recovering the unit if I do manage to get the lamp going again.
On 1/2/22 8:17 pm, Julien Goodwin wrote:
I picked up an Efratom FRT a while ago, and it finally arrived the
other day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear
someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few
days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first
stage op-amp from the photo-cell, so is this effectively an indication
that the (electrical part of the) lamp is dead? Certainly it wasn't
anywhere near the temperature it should have been when I removed the
bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up
cold with 24V, dropping down to about ~0.5A after a while. The sealed
sub-section of board A4 seems be where all the heat is, and I'm
assuming that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious
issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my
working house standard I'm somewhat loath to open it up lest I end up
with two dead units and zero working.
Any suggestions?
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe
send an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe
send an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
On 4/2/22 5:15 pm, Julien Goodwin wrote:
> Well that was unexpectedly easy (to diagnose).
>
> Thanks all for the replies, much appreciated, you have once again
> confirmed my appreciation for this group.
>
> I sat down this evening to work through your various suggestions, and,
> by chance, picked up the unit without my lab power supply (and more
> importantly, its noisy fans) being on, where I heard a little rattle I
> must have missed before.
>
> Removed the bottom panel, which I hadn't done yet, and out dropped the
> remnants of a Vishay RW80U 20-ohm resistor. Based on the circuit this
> pretty much has to be R2 on the lamp board (following the December 73
> circuit I have, which has that at 10 ohms), which is directly in-circuit
> for the lamp, so would explain exactly what I've seen.
Or, following the FRK-L schematic[1] it is indeed a 20 ohm 2W wirewound
(R14). All the other unused holes on the PCB lack obvious signs of
component legs, so that might be it.
I shall see what I can scrounge up at the local electronics shop
tomorrow[2] to see if I can bodge enough to test, hopefully without
needing to remove the board. Glad I had new tips for my tiny precision
iron show up today, might just be possible.
1: The FRK-L seems closer in some way than the original, although in
others the original is. This is labelled an FRK-H "made in West Germany"
which certainly dates it.
2: Tens of thousands of surface mount resistors here, but almost no
through hole.
> The lamp board in general seems to have a few holes missing components,
> so I'm going to have to get it out which looks like a project in itself.
>
> If anyone has any pointers to decent guides on optimum process on
> further disassembly, otherwise I guess it's copious photos, notes, and
> hoping I don't stuff up anything too much.
>
> I'd also appreciate suggestions for replacement foam to use in the lamp
> cavity as the original stuff has long since degraded.
>
> Paul, Peter Robert,
> Thanks for reinforcing what I'd suspected with the lamp.
>
> Matthias,
> I hadn't bothered with an actual temperature meter, luckily on the FRT
> it's actually easy to confirm lamp temperature in use, and it certainly
> wasn't anywhere near 100c. I think what heat there was likely leaked
> through from the crystal oven, which was getting pretty hot.
>
> Bob,
> Fortunately the onboard crystal does seem likely to still be close
> enough, based on what I was seeing on a counter, so I feel like I have a
> hope of recovering the unit if I do manage to get the lamp going again.
>
> On 1/2/22 8:17 pm, Julien Goodwin wrote:
>> I picked up an Efratom FRT a while ago, and it finally arrived the
>> other day, sadly it doesn't lock.
>>
>> The oscillator inside is an older Efratom FRK, and it's also clear
>> someone had been inside already, although it does appear to be complete.
>>
>> The FRK manual does include a key description I wish I'd noticed a few
>> days ago before full disassembly:
>>
>> "Terminal pin 7 provides an indication of proper operation of the
>> rubidium lamp. For nominal operation the signal is 6 to 12V. An
>> inoperative lamp is indicated by an signal of approximately 3V. The
>> internal resistance of this circuit is approximately 6K."
>>
>> ... indeed I'm seeing 3v on that pin.
>>
>> Based on the circuit this appears to simply be the output of the first
>> stage op-amp from the photo-cell, so is this effectively an indication
>> that the (electrical part of the) lamp is dead? Certainly it wasn't
>> anywhere near the temperature it should have been when I removed the
>> bulb after running for over an hour.
>>
>> Just for completeness, the unit does draw up to ~0.8A when started up
>> cold with 24V, dropping down to about ~0.5A after a while. The sealed
>> sub-section of board A4 seems be where all the heat is, and I'm
>> assuming that's an ovenised part of the crystal oscillator.
>>
>> I also popped the rubidium bulb out and confirmed there's no obvious
>> issues there.
>>
>> I do have another FRK here, but as it's an FRK-LN, and it's also my
>> working house standard I'm somewhat loath to open it up lest I end up
>> with two dead units and zero working.
>>
>> Any suggestions?
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe
>> send an email to time-nuts-leave@lists.febo.com
>> To unsubscribe, go to and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe
> send an email to time-nuts-leave@lists.febo.com
> To unsubscribe, go to and follow the instructions there.
PS
paul swed
Fri, Feb 4, 2022 3:58 PM
Julien
I don't think I would read a lot into the failed R just replace it. They
are in a nasty hot environment and simply can age and die. Get at leat 2
resistors just incase there really is a shorted transistor or something
else going on.
Regards
Paul
On Fri, Feb 4, 2022 at 3:50 AM Julien Goodwin time-nuts@studio442.com.au
wrote:
Well that was unexpectedly easy (to diagnose).
Thanks all for the replies, much appreciated, you have once again
confirmed my appreciation for this group.
I sat down this evening to work through your various suggestions, and,
by chance, picked up the unit without my lab power supply (and more
importantly, its noisy fans) being on, where I heard a little rattle I
must have missed before.
Removed the bottom panel, which I hadn't done yet, and out dropped the
remnants of a Vishay RW80U 20-ohm resistor. Based on the circuit this
pretty much has to be R2 on the lamp board (following the December 73
circuit I have, which has that at 10 ohms), which is directly in-circuit
for the lamp, so would explain exactly what I've seen.
The lamp board in general seems to have a few holes missing components,
so I'm going to have to get it out which looks like a project in itself.
If anyone has any pointers to decent guides on optimum process on
further disassembly, otherwise I guess it's copious photos, notes, and
hoping I don't stuff up anything too much.
I'd also appreciate suggestions for replacement foam to use in the lamp
cavity as the original stuff has long since degraded.
Paul, Peter Robert,
Thanks for reinforcing what I'd suspected with the lamp.
Matthias,
I hadn't bothered with an actual temperature meter, luckily on the FRT
it's actually easy to confirm lamp temperature in use, and it certainly
wasn't anywhere near 100c. I think what heat there was likely leaked
through from the crystal oven, which was getting pretty hot.
Bob,
Fortunately the onboard crystal does seem likely to still be close
enough, based on what I was seeing on a counter, so I feel like I have a
hope of recovering the unit if I do manage to get the lamp going again.
On 1/2/22 8:17 pm, Julien Goodwin wrote:
I picked up an Efratom FRT a while ago, and it finally arrived the other
day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear
someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few
days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first
stage op-amp from the photo-cell, so is this effectively an indication
that the (electrical part of the) lamp is dead? Certainly it wasn't
anywhere near the temperature it should have been when I removed the
bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up
cold with 24V, dropping down to about ~0.5A after a while. The sealed
sub-section of board A4 seems be where all the heat is, and I'm assuming
that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious
issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my
working house standard I'm somewhat loath to open it up lest I end up
with two dead units and zero working.
Any suggestions?
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe
send an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
Julien
I don't think I would read a lot into the failed R just replace it. They
are in a nasty hot environment and simply can age and die. Get at leat 2
resistors just incase there really is a shorted transistor or something
else going on.
Regards
Paul
On Fri, Feb 4, 2022 at 3:50 AM Julien Goodwin <time-nuts@studio442.com.au>
wrote:
> Well that was unexpectedly easy (to diagnose).
>
> Thanks all for the replies, much appreciated, you have once again
> confirmed my appreciation for this group.
>
> I sat down this evening to work through your various suggestions, and,
> by chance, picked up the unit without my lab power supply (and more
> importantly, its noisy fans) being on, where I heard a little rattle I
> must have missed before.
>
> Removed the bottom panel, which I hadn't done yet, and out dropped the
> remnants of a Vishay RW80U 20-ohm resistor. Based on the circuit this
> pretty much has to be R2 on the lamp board (following the December 73
> circuit I have, which has that at 10 ohms), which is directly in-circuit
> for the lamp, so would explain exactly what I've seen.
>
> The lamp board in general seems to have a few holes missing components,
> so I'm going to have to get it out which looks like a project in itself.
>
> If anyone has any pointers to decent guides on optimum process on
> further disassembly, otherwise I guess it's copious photos, notes, and
> hoping I don't stuff up anything too much.
>
> I'd also appreciate suggestions for replacement foam to use in the lamp
> cavity as the original stuff has long since degraded.
>
> Paul, Peter Robert,
> Thanks for reinforcing what I'd suspected with the lamp.
>
> Matthias,
> I hadn't bothered with an actual temperature meter, luckily on the FRT
> it's actually easy to confirm lamp temperature in use, and it certainly
> wasn't anywhere near 100c. I think what heat there was likely leaked
> through from the crystal oven, which was getting pretty hot.
>
> Bob,
> Fortunately the onboard crystal does seem likely to still be close
> enough, based on what I was seeing on a counter, so I feel like I have a
> hope of recovering the unit if I do manage to get the lamp going again.
>
> On 1/2/22 8:17 pm, Julien Goodwin wrote:
> > I picked up an Efratom FRT a while ago, and it finally arrived the other
> > day, sadly it doesn't lock.
> >
> > The oscillator inside is an older Efratom FRK, and it's also clear
> > someone had been inside already, although it does appear to be complete.
> >
> > The FRK manual does include a key description I wish I'd noticed a few
> > days ago before full disassembly:
> >
> > "Terminal pin 7 provides an indication of proper operation of the
> > rubidium lamp. For nominal operation the signal is 6 to 12V. An
> > inoperative lamp is indicated by an signal of approximately 3V. The
> > internal resistance of this circuit is approximately 6K."
> >
> > ... indeed I'm seeing 3v on that pin.
> >
> > Based on the circuit this appears to simply be the output of the first
> > stage op-amp from the photo-cell, so is this effectively an indication
> > that the (electrical part of the) lamp is dead? Certainly it wasn't
> > anywhere near the temperature it should have been when I removed the
> > bulb after running for over an hour.
> >
> > Just for completeness, the unit does draw up to ~0.8A when started up
> > cold with 24V, dropping down to about ~0.5A after a while. The sealed
> > sub-section of board A4 seems be where all the heat is, and I'm assuming
> > that's an ovenised part of the crystal oscillator.
> >
> > I also popped the rubidium bulb out and confirmed there's no obvious
> > issues there.
> >
> > I do have another FRK here, but as it's an FRK-LN, and it's also my
> > working house standard I'm somewhat loath to open it up lest I end up
> > with two dead units and zero working.
> >
> > Any suggestions?
> > _______________________________________________
> > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe
> > send an email to time-nuts-leave@lists.febo.com
> > To unsubscribe, go to and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send
> an email to time-nuts-leave@lists.febo.com
> To unsubscribe, go to and follow the instructions there.
>
JG
Julien Goodwin
Sat, Feb 5, 2022 9:48 AM
On 5/2/22 2:58 am, paul swed wrote:
Julien
I don't think I would read a lot into the failed R just replace it. They
are in a nasty hot environment and simply can age and die. Get at leat 2
resistors just incase there really is a shorted transistor or something
else going on.
Regards
Paul
Oh absolutely, my rough guess is the thermal insulation foam degraded
corroding the leads /eventually/. This unit is over 30 years old, and
who knows how it was used, although being in a road case makes me
suspect it was not the sort of life we might like.
I swapped in two 10-ohm 1-watt carbon film resistors today (being what I
could get my hands on).
Sadly I couldn't just solder to the lead stubs still poking through the
board, they were just too corroded. A significant disassembly and
reassembly later the unit appears to be improved, but still not locking.
Should anyone run into this later, a clear bench, lots of lighting, and
a way to ensure any screw you drop doesn't disappear never to be seen
again are strongly recommended. Sadly my own bench is rather more of the
Jim Williams[1] variety. A good soldering setup is also needed, but
there I was rather luckier, even if my new desoldering iron did end up
lifting a few pads.
I /think/ it's using more power than it did before (right around 20W at
total cold, dipping to 10W after a while), although silly me didn't make
a note of it, but even after 30 minutes it's not locking.
Given that the resistor I replaced is in a key point for the lamp
excitation oscillator I won't be surprised if it's totally off and needs
a recalibration, but that's a task for another day. When I stick a scope
probe in the lamp cavity as the manual suggests I do see a a signal, so
there's certainly hope, although I don't see the expected glow.
I did confirm the heater is working, and was getting above 90c when I
poked a thermocouple at it just after power-off.
1: https://www.edn.com/honoring-jim-williams/
On Fri, Feb 4, 2022 at 3:50 AM Julien Goodwin time-nuts@studio442.com.au
wrote:
Well that was unexpectedly easy (to diagnose).
Thanks all for the replies, much appreciated, you have once again
confirmed my appreciation for this group.
I sat down this evening to work through your various suggestions, and,
by chance, picked up the unit without my lab power supply (and more
importantly, its noisy fans) being on, where I heard a little rattle I
must have missed before.
Removed the bottom panel, which I hadn't done yet, and out dropped the
remnants of a Vishay RW80U 20-ohm resistor. Based on the circuit this
pretty much has to be R2 on the lamp board (following the December 73
circuit I have, which has that at 10 ohms), which is directly in-circuit
for the lamp, so would explain exactly what I've seen.
The lamp board in general seems to have a few holes missing components,
so I'm going to have to get it out which looks like a project in itself.
If anyone has any pointers to decent guides on optimum process on
further disassembly, otherwise I guess it's copious photos, notes, and
hoping I don't stuff up anything too much.
I'd also appreciate suggestions for replacement foam to use in the lamp
cavity as the original stuff has long since degraded.
Paul, Peter Robert,
Thanks for reinforcing what I'd suspected with the lamp.
Matthias,
I hadn't bothered with an actual temperature meter, luckily on the FRT
it's actually easy to confirm lamp temperature in use, and it certainly
wasn't anywhere near 100c. I think what heat there was likely leaked
through from the crystal oven, which was getting pretty hot.
Bob,
Fortunately the onboard crystal does seem likely to still be close
enough, based on what I was seeing on a counter, so I feel like I have a
hope of recovering the unit if I do manage to get the lamp going again.
On 1/2/22 8:17 pm, Julien Goodwin wrote:
I picked up an Efratom FRT a while ago, and it finally arrived the other
day, sadly it doesn't lock.
The oscillator inside is an older Efratom FRK, and it's also clear
someone had been inside already, although it does appear to be complete.
The FRK manual does include a key description I wish I'd noticed a few
days ago before full disassembly:
"Terminal pin 7 provides an indication of proper operation of the
rubidium lamp. For nominal operation the signal is 6 to 12V. An
inoperative lamp is indicated by an signal of approximately 3V. The
internal resistance of this circuit is approximately 6K."
... indeed I'm seeing 3v on that pin.
Based on the circuit this appears to simply be the output of the first
stage op-amp from the photo-cell, so is this effectively an indication
that the (electrical part of the) lamp is dead? Certainly it wasn't
anywhere near the temperature it should have been when I removed the
bulb after running for over an hour.
Just for completeness, the unit does draw up to ~0.8A when started up
cold with 24V, dropping down to about ~0.5A after a while. The sealed
sub-section of board A4 seems be where all the heat is, and I'm assuming
that's an ovenised part of the crystal oscillator.
I also popped the rubidium bulb out and confirmed there's no obvious
issues there.
I do have another FRK here, but as it's an FRK-LN, and it's also my
working house standard I'm somewhat loath to open it up lest I end up
with two dead units and zero working.
Any suggestions?
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe
send an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send
an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
On 5/2/22 2:58 am, paul swed wrote:
> Julien
> I don't think I would read a lot into the failed R just replace it. They
> are in a nasty hot environment and simply can age and die. Get at leat 2
> resistors just incase there really is a shorted transistor or something
> else going on.
> Regards
> Paul
Oh absolutely, my rough guess is the thermal insulation foam degraded
corroding the leads /eventually/. This unit is over 30 years old, and
who knows how it was used, although being in a road case makes me
suspect it was not the sort of life we might like.
I swapped in two 10-ohm 1-watt carbon film resistors today (being what I
could get my hands on).
Sadly I couldn't just solder to the lead stubs still poking through the
board, they were just too corroded. A significant disassembly and
reassembly later the unit appears to be improved, but still not locking.
Should anyone run into this later, a clear bench, lots of lighting, and
a way to ensure any screw you drop doesn't disappear never to be seen
again are strongly recommended. Sadly my own bench is rather more of the
Jim Williams[1] variety. A good soldering setup is also needed, but
there I was rather luckier, even if my new desoldering iron did end up
lifting a few pads.
I /think/ it's using more power than it did before (right around 20W at
total cold, dipping to 10W after a while), although silly me didn't make
a note of it, but even after 30 minutes it's not locking.
Given that the resistor I replaced is in a key point for the lamp
excitation oscillator I won't be surprised if it's totally off and needs
a recalibration, but that's a task for another day. When I stick a scope
probe in the lamp cavity as the manual suggests I do see a a signal, so
there's certainly hope, although I don't see the expected glow.
I did confirm the heater is working, and was getting above 90c when I
poked a thermocouple at it just after power-off.
1: https://www.edn.com/honoring-jim-williams/
> On Fri, Feb 4, 2022 at 3:50 AM Julien Goodwin <time-nuts@studio442.com.au>
> wrote:
>
>> Well that was unexpectedly easy (to diagnose).
>>
>> Thanks all for the replies, much appreciated, you have once again
>> confirmed my appreciation for this group.
>>
>> I sat down this evening to work through your various suggestions, and,
>> by chance, picked up the unit without my lab power supply (and more
>> importantly, its noisy fans) being on, where I heard a little rattle I
>> must have missed before.
>>
>> Removed the bottom panel, which I hadn't done yet, and out dropped the
>> remnants of a Vishay RW80U 20-ohm resistor. Based on the circuit this
>> pretty much has to be R2 on the lamp board (following the December 73
>> circuit I have, which has that at 10 ohms), which is directly in-circuit
>> for the lamp, so would explain exactly what I've seen.
>>
>> The lamp board in general seems to have a few holes missing components,
>> so I'm going to have to get it out which looks like a project in itself.
>>
>> If anyone has any pointers to decent guides on optimum process on
>> further disassembly, otherwise I guess it's copious photos, notes, and
>> hoping I don't stuff up anything too much.
>>
>> I'd also appreciate suggestions for replacement foam to use in the lamp
>> cavity as the original stuff has long since degraded.
>>
>> Paul, Peter Robert,
>> Thanks for reinforcing what I'd suspected with the lamp.
>>
>> Matthias,
>> I hadn't bothered with an actual temperature meter, luckily on the FRT
>> it's actually easy to confirm lamp temperature in use, and it certainly
>> wasn't anywhere near 100c. I think what heat there was likely leaked
>> through from the crystal oven, which was getting pretty hot.
>>
>> Bob,
>> Fortunately the onboard crystal does seem likely to still be close
>> enough, based on what I was seeing on a counter, so I feel like I have a
>> hope of recovering the unit if I do manage to get the lamp going again.
>>
>> On 1/2/22 8:17 pm, Julien Goodwin wrote:
>>> I picked up an Efratom FRT a while ago, and it finally arrived the other
>>> day, sadly it doesn't lock.
>>>
>>> The oscillator inside is an older Efratom FRK, and it's also clear
>>> someone had been inside already, although it does appear to be complete.
>>>
>>> The FRK manual does include a key description I wish I'd noticed a few
>>> days ago before full disassembly:
>>>
>>> "Terminal pin 7 provides an indication of proper operation of the
>>> rubidium lamp. For nominal operation the signal is 6 to 12V. An
>>> inoperative lamp is indicated by an signal of approximately 3V. The
>>> internal resistance of this circuit is approximately 6K."
>>>
>>> ... indeed I'm seeing 3v on that pin.
>>>
>>> Based on the circuit this appears to simply be the output of the first
>>> stage op-amp from the photo-cell, so is this effectively an indication
>>> that the (electrical part of the) lamp is dead? Certainly it wasn't
>>> anywhere near the temperature it should have been when I removed the
>>> bulb after running for over an hour.
>>>
>>> Just for completeness, the unit does draw up to ~0.8A when started up
>>> cold with 24V, dropping down to about ~0.5A after a while. The sealed
>>> sub-section of board A4 seems be where all the heat is, and I'm assuming
>>> that's an ovenised part of the crystal oscillator.
>>>
>>> I also popped the rubidium bulb out and confirmed there's no obvious
>>> issues there.
>>>
>>> I do have another FRK here, but as it's an FRK-LN, and it's also my
>>> working house standard I'm somewhat loath to open it up lest I end up
>>> with two dead units and zero working.
>>>
>>> Any suggestions?
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